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Hello, looking for some assistance with a starting problem. My Exmark, model LZ28KC724 which I purchased in 2004 has developed its first problem. Two weeks ago when I went to start the mower, the indicator LED turned red as always, but the fuel pump did not kick on as usual. As a result, the mower would not start. After spending a good hour checking fuses and connections, on a whim, I connected my battery charger.

On the 10 amp charging setting, the same situation occurred. Keyswitch to on, red light, but no buzz indicating the fuel pump kicked on. Giving it one more shot, I changed the setting on the battery charger to the 55 amp "start" setting. Voila, the fuel pump buzzed, and the mower started. The mower continued to run until I finished and parked it back in the barn. On trying to restart it, the same thing occurred.

Based on the above, I installed a new battery. The old battery was 4 years old, so figured it didn't owe me anything. The battery shop tested the old battery, it had 215 CCA. The new battery was fully charged, and registered 320 CCA. Surprisingly, the new battery made no difference. I still have to connect the charger, on the 55 amp setting, in order to get the fuel pump to fire.

Anyone else run into this? I searched the forum before posting, but didn't find anything remotely related to this problem.

Thanks in advance, and happy Father's Day to all the dads out there!

A simple cleaning and tightening of your battery cables (BOTH ENDS especially the ground cable) along with being sure the start solenoid has a good ground and secure wires may be helpful.

Run a heavy jumper from the - battery terminal to the engine ( drain plug is a good place or the lifting hook ).
Mower fires right up then you have a bad ground.
On most mowers the ground is made by the 1.5 turns of thread on the bolt that is threaded into the body.
The frame is fully painted then the engine is fitted and the engine ground is basically a couple of scratches.
On a few "problem" mowers I have run a ground strap directly to one of the engine mounting bolts secured with a 1/2 nut.
The whole lot then gets painted with liquid electrical tape, as does the main ground , after striping the paint under it & fitting a new zinc plated bolt.
Battery terminals get the same treatment.
I fit longer battery bolts, paint the entire terminal to prevent corrosion leaving 1/2" of unpainted bolt protruding to allow for measuring & jump starting.

Boobala said:

A simple cleaning and tightening of your battery cables (BOTH ENDS especially the ground cable) along with being sure the start solenoid has a good ground and secure wires may be helpful.

Click to expand...

Thanks! I'll go through the wiring tomorrow morning. Too hot to do any outside work today, or even mow. Appreciate the response, and will let you know what if anything I find.

bertsmobile1 said:

Run a heavy jumper from the - battery terminal to the engine ( drain plug is a good place or the lifting hook ).
Mower fires right up then you have a bad ground.
On most mowers the ground is made by the 1.5 turns of thread on the bolt that is threaded into the body.
The frame is fully painted then the engine is fitted and the engine ground is basically a couple of scratches.
On a few "problem" mowers I have run a ground strap directly to one of the engine mounting bolts secured with a 1/2 nut.
The whole lot then gets painted with liquid electrical tape, as does the main ground , after striping the paint under it & fitting a new zinc plated bolt.
Battery terminals get the same treatment.
I fit longer battery bolts, paint the entire terminal to prevent corrosion leaving 1/2" of unpainted bolt protruding to allow for measuring & jump starting.

Click to expand...

Thank you! That kind of situation might account for why I can get the mower to start when using the battery charger on the 55 amp setting, but not the 10 amp. The additional current might be the difference in getting a complete circuit. Strange that it would manifest after 14 years, and from one start to the next, but I have seen stranger things. Thanks for the reply. Greatly appreciated, and I'll provide feedback.

mowerman556 said:

Thank you! That kind of situation might account for why I can get the mower to start when using the battery charger on the 55 amp setting, but not the 10 amp. The additional current might be the difference in getting a complete circuit. Strange that it would manifest after 14 years, and from one start to the next, but I have seen stranger things. Thanks for the reply. Greatly appreciated, and I'll provide feedback.

Click to expand...

Not strange at all.
Over time the original nice clean bolt rusts as dose the the body so the grounding slowly gets worse.
Because this happens slowly ove time you don't notice till one day it wont start at all.

FWIW it is always bet to jump to the + battery terminal and a good ground point on the motor.
I had a mower come in because the throttle wire was burning.
And sure enough smoke poured out of it when you started the mower and it was way too hot to touch, and yes the throttle wire was the only ground path to the engine.

** Update to original post **

So, with input from Boobola and bertsmobile1 I cleaned the connections yesterday morning. I also made up a jumper wire with ring connectors on both ends. With one end connected to the battery negative post, I connected the other end of the jumper wirer to various points:

* The same lug on the engine as the wire from the battery
* The engine lifting hook
* Several areas of the frame
*The bolt that secures the muffler to the engine

Same condition each time, that is to say, no change. Each time I relocated the jumper wire I turned the key to the ON position but the fuel pump still did not cycle. I removed the jumper wire from the battery and set it aside. Connecting the battery charger, and being on the 55A "start" setting, the fuel pump cycled and the mower started. So, mowed that way yesterday, just cautious not to shut it off along the way. Soon as I parked it back in the barn and turned the key... nothing. Fuel pump doesn't cycle.

Oh, one more thing I did... unplugged the large plug on the left side, it's about a 50 pin or so connector. I assume this is where the ECU is located? I looked over the plug, it was clean, could not see any pushed pins, and it was still "slick" from dielectric grease, which I assume has been there since it was built. Reconnected it, and still no change.

Any other suggestions? Could the problem be a voltage regulator? Where is it located, and how do I test it?

thanks again,

mowerman556

Replace the starter

GrassBarber said:

Replace the starter

Click to expand...

Thanks, GrassBarber. Can you give me any more to go on? Is this something that's you've experienced? Is there a way to test the starter without replacing it first?

The reason that I ask is because the engine turns over and over with no problem with the key in the start position. It's just that it will only "fire" when the battery charger is hooked up, and only on the 55A setting. If I have it on the 10A setting for example, the mower cranks and cranks but still won't "fire". Here is what I've found in the Kohler Service manual which I found online:

When key switch is turned ON and all safety switch
requirements are met, ECU activates fuel pump module
for about six seconds, which pressurizes system for
start-up. If key switch is not promptly turned to start
position, engine fails to start, or engine is stopped with
key switch ON (as in case of an accident), ECU switches
off pump preventing continued delivery of fuel. In this
situation, MIL will go on, but it will go back off after 4
cranking revolutions if system function is OK. Once
engine is running, fuel pump remains on.

I'm not getting the six second buzz for the fuel pump module when I turn the key to the "on" position UNLESS the charger is connected, and on the 55A setting.

Thanks!

Sounds like a bad electrical connection with possible corrosion. Remove and clean all the grounds that you can find on the engine. Pay special attention to the ECU ground wires also.

No the problem can not be the voltage regulator.
The fuel pump should have a black & a purple wire attached to it ( if I have the correct diagram )
The black wire goes to the PTO Clutch then to it's own ground
So working on the bad ground theory check for ground on the black wire at the pump.

The purple wire goes into the engine so will be on a switch of some sort, most likely a pressure switch on the fuel line or a control relay.
To take that any further I will need the full engine number to see If we can't find the Kohler engine wiring circuit.
You could remove the engine cover to see where the purple wire goes, but I fear it will be into an ECU which will be a replace only item.

mowerman556 said:

Thanks, GrassBarber. Can you give me any more to go on? Is this something that's you've experienced? Is there a way to test the starter without replacing it first?

The reason that I ask is because the engine turns over and over with no problem with the key in the start position. It's just that it will only "fire" when the battery charger is hooked up, and only on the 55A setting. If I have it on the 10A setting for example, the mower cranks and cranks but still won't "fire". Here is what I've found in the Kohler Service manual which I found online:

When key switch is turned ON and all safety switch
requirements are met, ECU activates fuel pump module
for about six seconds, which pressurizes system for
start-up. If key switch is not promptly turned to start
position, engine fails to start, or engine is stopped with
key switch ON (as in case of an accident), ECU switches
off pump preventing continued delivery of fuel. In this
situation, MIL will go on, but it will go back off after 4
cranking revolutions if system function is OK. Once
engine is running, fuel pump remains on.

I'm not getting the six second buzz for the fuel pump module when I turn the key to the "on" position UNLESS the charger is connected, and on the 55A setting.

Thanks!

Click to expand...

Don’t replace the starter, I’m having reading comprehension issues. Miss the “engine turns over”

My apologies

bertsmobile1 said:

No the problem can not be the voltage regulator.
The fuel pump should have a black & a purple wire attached to it ( if I have the correct diagram )
The black wire goes to the PTO Clutch then to it's own ground
So working on the bad ground theory check for ground on the black wire at the pump.

The purple wire goes into the engine so will be on a switch of some sort, most likely a pressure switch on the fuel line or a control relay.
To take that any further I will need the full engine number to see If we can't find the Kohler engine wiring circuit.
You could remove the engine cover to see where the purple wire goes, but I fear it will be into an ECU which will be a replace only item.

Click to expand...

Thanks for the info. I'm out of pocket for a few days with elder care issues. I will get back into this early next week (June 25-26), and let you know what I find. The engine is a CH745. The serial number is rubbed off from the rubber cover that hides the engine shaft vibrating against it over the past 14 years (remember this mower is in a residential setting, and I use it once a week in summer, twice a week in wet weather. FWIW, it is always stored indoors, and kept under mild heat (40 degrees-ish) when the temps dip below 10F or so.) Is the serial number located anywhere else?

More next week,

mowerman556

No problem, GrassBarber. Done it on more than one occasion myself. have a good weekend!

bertsmobile1 said:

No the problem can not be the voltage regulator.
The fuel pump should have a black & a purple wire attached to it ( if I have the correct diagram )
The black wire goes to the PTO Clutch then to it's own ground
So working on the bad ground theory check for ground on the black wire at the pump.

The purple wire goes into the engine so will be on a switch of some sort, most likely a pressure switch on the fuel line or a control relay.
To take that any further I will need the full engine number to see If we can't find the Kohler engine wiring circuit.
You could remove the engine cover to see where the purple wire goes, but I fear it will be into an ECU which will be a replace only item.

Click to expand...

With apologies for the delay, I got back into the mower this morning. Connections all checked out okay. On finding the fuel pump, it does have a black and a purple wire on the terminals. I placed a DC volt meter on the purple lead and ground (chassis) with the key in the on position. I did not get the 6 second fuel pump buzz, which has been the problem all along. The volt meter read zero volts. I then put the battery charger across the battery terminals on the 55A setting. When I turned the key, the fuel pump buzzed as it should. Taking the same DC voltage reading between fuel pump purple wire at the terminal and chassis ground, I had a good 12 vdc reading. Hope this helps narrow things down?

The engine serial number is 3303900991. That's on the triangular cover plate on the front of the motor, close to the intake manifold. Engine model is PS-CH745-0003 Note there is the gray "box" secured to the left inner side of the frame. That has a different engine serial number on it? that one says 3409613431.

Any further thoughts would be appreciated, and again, TIA!

Personally, I have found that the electrical systems on mowers, cars, trucks, etc. will benefit from adding hyper grounds. These are added ground wires from the battery negative anode(connection) to the chassis and engine. Cleaning the connections points well and then adding a generous dab of di-electric grease after the connection is made will add reliability. This reduces corrosion. No matter what, electrical issues on our machines can typically be traced to a corroded connection, whether ground or hot. As an example, my 2006 Japanese made motorcycle began experiencing an electrical issue that was driving me mad. Symptom began when activating the turn signal which would cause the engine to surge and feel as though it was misfiring, then it escalated to stalling when I applied the brakes. What the heck? Long story short, the culprit was a badly corroded ground connector about 8" from the negative battery anode. It was so corroded that once I forced the connector apart, it disintegrated in my hand. I had to cut the connector out and use a WAGO connector in its place. I also used a heavier gauge marine gauge wire to reestablish this important ground. Not only was the problem solved, but I notice that the engine starter spins the engine quicker and the engine starts immediately vs a few seconds before. Lesson is that a good strong ground is super important.

Boit4852 said:

Personally, I have found that the electrical systems on mowers, cars, trucks, etc. will benefit from adding hyper grounds. These are added ground wires from the battery negative anode(connection) to the chassis and engine. Cleaning the connections points well and then adding a generous dab of di-electric grease after the connection is made will add reliability. This reduces corrosion. No matter what, electrical issues on our machines can typically be traced to a corroded connection, whether ground or hot. As an example, my 2006 Japanese made motorcycle began experiencing an electrical issue that was driving me mad. Symptom began when activating the turn signal which would cause the engine to surge and feel as though it was misfiring, then it escalated to stalling when I applied the brakes. What the heck? Long story short, the culprit was a badly corroded ground connector about 8" from the negative battery anode. It was so corroded that once I forced the connector apart, it disintegrated in my hand. I had to cut the connector out and use a WAGO connector in its place. I also used a heavier gauge marine gauge wire to reestablish this important ground. Not only was the problem solved, but I notice that the engine starter spins the engine quicker and the engine starts immediately vs a few seconds before. Lesson is that a good strong ground is super important.

Click to expand...

Bolt might have it.
On more than one occasion I heave needed to run an extra ground to the engine to get a mower to behave.

Boit4852 said:

Personally, I have found that the electrical systems on mowers, cars, trucks, etc. will benefit from adding hyper grounds. These are added ground wires from the battery negative anode(connection) to the chassis and engine. Cleaning the connections points well and then adding a generous dab of di-electric grease after the connection is made will add reliability. This reduces corrosion. No matter what, electrical issues on our machines can typically be traced to a corroded connection, whether ground or hot. As an example, my 2006 Japanese made motorcycle began experiencing an electrical issue that was driving me mad. Symptom began when activating the turn signal which would cause the engine to surge and feel as though it was misfiring, then it escalated to stalling when I applied the brakes. What the heck? Long story short, the culprit was a badly corroded ground connector about 8" from the negative battery anode. It was so corroded that once I forced the connector apart, it disintegrated in my hand. I had to cut the connector out and use a WAGO connector in its place. I also used a heavier gauge marine gauge wire to reestablish this important ground. Not only was the problem solved, but I notice that the engine starter spins the engine quicker and the engine starts immediately vs a few seconds before. Lesson is that a good strong ground is super important.

Click to expand...

Thanks Boit4852. Already added the extra ground, and no change in the symptom. Again, under normal operation when the key is turned to "on" position the fuel pump should run for six seconds, then stop, after which the key can be turned to the start position to start the engine. In my case, the fuel pump does not cycle for those six seconds. Nothing happens. Obviously, without that "prime", if I turn the key to "start" position the engine cranks and cranks, but will not fire.

From Bertsmobile1's earlier comments I did add a secondary ground wire see pic), of the same or similar gauge as the factory wire. I attached this to the same lug on the engine that the battery negative is connected to. I also then connected the other end (under existing nut or bolt) to various parts of the engine, including the lifting hook, and to various parts of the frame. In ALL cases, when I turn the key to "on", the fuel pump still did not cycle for six seconds as it should. I also left the key in the "on" position, and with the other end of auxiliary ground wire loose in my hand, I did a "touch test" to various parts of the engine and the frame. Same situation, fuel pump does not cycle.

Further troubleshooting, I found that when I turn the key to the "on" position, the terminal with the purple wire on the fuel pump reads 0 volts DC.

The only way the engine will start is when I put a battery charger across the battery, on the 55A setting. When I do that and turn the key to the "on" position the fuel pump cycles, and the engine starts. In that situation, the purple wire on the fuel pump also has 12 VDC on it.

I thought about relays, but that doesn't make sense for why the battery charger starts the mower. Once the engine starts, I can mow for 2-3 hours with absolutely no issues whatsoever. Soon as I turn it off, however, it will not start again without the battery charger on it. (I had replaced the battery already, if you hadn't read back.)

I'm starting to think ECU.... thoughts?

Thanks,

mowerman556

Well it does sound like the ECU is on the way out.
OTOH it is an expensive piece of kit to replace if there is nothing wrong with it.
On the nigh charge setting the output voltage on your charger is going to be around 14V if not more untill a heavy load is put on it.
This tends to favour a voltage drop somewhere between the battery and the ECU but we are running out of options.
You may have a wire broken at a terminal but we are getting into the drowning man clutching at straws territory now.

mowerman556 said:

View attachment 39203

Thanks Boit4852. Already added the extra ground, and no change in the symptom. Again, under normal operation when the key is turned to "on" position the fuel pump should run for six seconds, then stop, after which the key can be turned to the start position to start the engine. In my case, the fuel pump does not cycle for those six seconds. Nothing happens. Obviously, without that "prime", if I turn the key to "start" position the engine cranks and cranks, but will not fire.

From Bertsmobile1's earlier comments I did add a secondary ground wire see pic), of the same or similar gauge as the factory wire. I attached this to the same lug on the engine that the battery negative is connected to. I also then connected the other end (under existing nut or bolt) to various parts of the engine, including the lifting hook, and to various parts of the frame. In ALL cases, when I turn the key to "on", the fuel pump still did not cycle for six seconds as it should. I also left the key in the "on" position, and with the other end of auxiliary ground wire loose in my hand, I did a "touch test" to various parts of the engine and the frame. Same situation, fuel pump does not cycle.

Further troubleshooting, I found that when I turn the key to the "on" position, the terminal with the purple wire on the fuel pump reads 0 volts DC.

The only way the engine will start is when I put a battery charger across the battery, on the 55A setting. When I do that and turn the key to the "on" position the fuel pump cycles, and the engine starts. In that situation, the purple wire on the fuel pump also has 12 VDC on it.

I thought about relays, but that doesn't make sense for why the battery charger starts the mower. Once the engine starts, I can mow for 2-3 hours with absolutely no issues whatsoever. Soon as I turn it off, however, it will not start again without the battery charger on it. (I had replaced the battery already, if you hadn't read back.)

I'm starting to think ECU.... thoughts?

Thanks,

mowerman556

Click to expand...

You've taken a good first step to solve this issue. To respond to your comment about the relay, let me add info about my recent experience with the starter relay on the motorcycle I mentioned in my other post. Starter relays is nothing more than a switch that 'relays' high current to the starter motor. Sounds to that the high current contacts inside the relay have finally either corroded or have worn out to the point that the relay won't send enough current to spin the starter motor to start the engine. My motorcycle is a '06 Suzuki that due to age, is beginning to have issues. Along with making my own grounds, I also changed the starter relay. It was the original relay. The high current contacts DO corrode and wear out. By you using the high amp charger, that forces high current across those contacts that you are not getting form the battery and you can start the engine. Once it is running and you release the ignition key, the starter relay breaks current across the contacts to the starter motor and has zero effect on whether the engine runs or not. My recommendation is to test the starter relay or just replace it. These relays are more expensive than a run of the mill relay. These are specialized. The starter relay for my Suzuki was nearly $80. I changed the relay on my Exmark last year and if my memory is correct, it was under $40.

I mentioned the starter and I thought the OP tested it

The starter is turning, what is happening is the fuel pump is not priming the system.
It is a fuel injected engine.

The last cheap item would be the fuel pressure gauge but from memory it is a just a spring loaded bypass.
If there is a wire hanging out of it then that piece of kit could be faulty and registering full pressure when there is none but as before it is another clutching at straws job.
I do not have the error codes for your engine which would be the next step to see if the system is registering a sensor fault.
Will have a dig around the hard drive latter to see what comes up.

Boit4852 said:

You've taken a good first step to solve this issue. To respond to your comment about the relay, let me add info about my recent experience with the starter relay on the motorcycle I mentioned in my other post. Starter relays is nothing more than a switch that 'relays' high current to the starter motor. Sounds to that the high current contacts inside the relay have finally either corroded or have worn out to the point that the relay won't send enough current to spin the starter motor to start the engine. My motorcycle is a '06 Suzuki that due to age, is beginning to have issues. Along with making my own grounds, I also changed the starter relay. It was the original relay. The high current contacts DO corrode and wear out. By you using the high amp charger, that forces high current across those contacts that you are not getting form the battery and you can start the engine. Once it is running and you release the ignition key, the starter relay breaks current across the contacts to the starter motor and has zero effect on whether the engine runs or not. My recommendation is to test the starter relay or just replace it. These relays are more expensive than a run of the mill relay. These are specialized. The starter relay for my Suzuki was nearly $80. I changed the relay on my Exmark last year and if my memory is correct, it was under $40.

Click to expand...

Thanks for the additional info, Boit4852. For $40, I'll get a starter relay from the local dealer and see what if that helps. I agree with the high resistance relay contacts. I'm thinking about the ECU along those lines... The silicon barriers in IC chips (known as P-N junctions) can break down without being a hard failure. I saw a description decades ago which showed the PN junction as a brick wall, and over time, some of the bricks loosening and falling out, either allowing leakage or not passing current at proper times. In that vein, the higher current "forces" the signal through the P-N junction, completing the circuit. Should this be the case, the IC will completely fail at some point, at which time no amount of current would allow a signal to pass. (Back in the early days I used to do component level circuit board repair... with an oscilloscope.)

I'll report back after I get a relay in install it. I assume it's externally mounted? Or is it?

bertsmobile1 said:

The starter is turning, what is happening is the fuel pump is not priming the system.
It is a fuel injected engine.

The last cheap item would be the fuel pressure gauge but from memory it is a just a spring loaded bypass.
If there is a wire hanging out of it then that piece of kit could be faulty and registering full pressure when there is none but as before it is another clutching at straws job.
I do not have the error codes for your engine which would be the next step to see if the system is registering a sensor fault.
Will have a dig around the hard drive latter to see what comes up.

Click to expand...

Thanks Bertsmobile1. I saw your note here after I responded to boit4852. Am I to assume from your comment that because the starter is turning I can safely ignore the starter relay replacement?

Regarding the fuel pressure gauge... I don't have one? There are no gauges on my Exmark whatsoever, unless we consider the hour meter to be a gauge (of sorts). Where would I find this wire hanging out of a fuel pressure device to check for a wire hanging from it?

Back to the earlier train of thought, I looked online for a replacement ECU and nearly fell out of my chair.... two sources, and $1,003 USD at each. Holy cats. Is there an Exmark salvage yard or used parts emporium online that I haven't found from my poking around yet?

Thanks,

mowerman556

It could still be the starter (as was mentioned, to replace)...is the lug where the battery connects getting hot when you try to start it?
Does it turn normal speed or very slow?

A bad starter can pull a lot of amps.

shiftsuper175607 said:

It could still be the starter (as was mentioned, to replace)...is the lug where the battery connects getting hot when you try to start it?
Does it turn normal speed or very slow?

A bad starter can pull a lot of amps.

Click to expand...

I will temp test the battery lug on the engine after attempting to start it a few times. Everything sounds correct, including cranking speed, only the mower won't start. The mower does not have the fuel pump prime when the key is turned to "on" position". When I add the battery charger (on 55A setting), the fuel pump primes and the mower starts, and runs normally after that (for hours). If I shut it off, however, it will not fire again unless the charger is connected again. It will however, crank and crank and crank (sounding normal), just no fire. Battery is new. Wiring and connections have been tested half a dozen times.

shiftsuper175607 said:

It could still be the starter (as was mentioned, to replace)...is the lug where the battery connects getting hot when you try to start it?
Does it turn normal speed or very slow?

A bad starter can pull a lot of amps.

Click to expand...

Hi shiftsuper175607 The battery lead on the engine lug does not get hot whatsoever when cranking. As soon as I connect the battery charger, the engine fires immediately, like on the first revolution or two.

Would a bad starter pulling a lot of amps prevent the fuel pump from priming the system? That's the root problem... no fuel prime for the six seconds when the key is turned to "on". When I connect the charger, the engine fires right now.

For what its worth, the mower is always stored indoors, and only used by me for residential mowing of four acres. It never gets wet except for the times I wash it, which hasn't been since earlier this summer and well before this problem started. The mower is a 2003 model, and has about 825 hours on it. 28hp Kohler EFI.

Thanks.

mowerman556 said:

Hi shiftsuper175607 The battery lead on the engine lug does not get hot whatsoever when cranking. As soon as I connect the battery charger, the engine fires immediately, like on the first revolution or two.

Would a bad starter pulling a lot of amps prevent the fuel pump from priming the system? That's the root problem... no fuel prime for the six seconds when the key is turned to "on". When I connect the charger, the engine fires right now.

For what its worth, the mower is always stored indoors, and only used by me for residential mowing of four acres. It never gets wet except for the times I wash it, which hasn't been since earlier this summer and well before this problem started. The mower is a 2003 model, and has about 825 hours on it. 28hp Kohler EFI.

Thanks.

Click to expand...

You have an unusual and interesting problem.
I considered the starter problem because something seems to bedrawing the voltage down low enough that is preventing the fuel pump/relay fromoperating as it should.
Keep working at it and hopefully you will get this solvedwith a lot of help. Please let us know how it turns out. This is quite a headscratcher.

As Supershift mentioned, something is causing a large enough voltage drop when trying to start the enjoy with only the battery. One easy test is to hook up a meter at the battery and see what voltage reads at rest. Should be ~12.4 to 12.8 range. While keeping the meter hooked up, crank the engine while reading the meter and see how low the voltage drops. Write that down if your memory is as bad as mine. As was mentioned, if the voltage is too low while cranking, the fuel pump relay probably won’t operate and the fuel pump won’t run thusly, the engine won’t start. If you see voltage much below 10v, there is excessive draw while cranking and that certainly could be the starter motor along as the battery is good. Most auto parts stores will test your battery and starter for free if you are willing to remove the starter yourself. I’ve had my starter off a few times and can do it now quickly. Yours might more difficult. Makes it easier if you jack it up on that side and remove the wheel.

What both you & Super are missing is the fuel pump should pump up the system when the switch is turned ON way before he hits the Start Position
If you own a fuel injected car you have the same system.
When the key gets turned to the on position the fuel pump kicks in to pressurise the system.
This is what is not happening.
The pump relay is not firing up the pump unless the battery charger is on a very high setting and would be over voltage.

Depending upon which system he has either the ECU is duff, or the fuel pressure sensor ( if it has one ) is not sending a low pressure signal to the ECU so it fires up the pump.

So from here on Mowerman556 will have to go to the Kohler web site & download the service manual for his mower.
As he mentioned a "plug with about 40 pins" I will assume he has the 32 pin Bosch controller on his mower.
We have gone through all the easy stuff, now it will be a case of running the fuel pump control circuit diagnostics,
AS he has not mentioned an error code this would tend towards a problem with the ECU itself .

We do not know which engine & which injection system Mowerman has and even if he did there is very little I can do from here on.
The pump is in fact working and at some point the controls for the pump are working but the start up cycle is not unless the system gets an overwhelming voltage.

This normally would suggest a bad connection somewhere but he has done all of the jumping from the battery that he can so now we are left with the ECU & the pump relay, if the later is not part of the ECU or possibly the Fuel pressure sensor ( should it have one ).
According to how I interpret the manuals I have the unit should be showing a service warning if the pump , relay or pressure controller are bad and he is not getting one.
All that can be done now is to see if the ECU is putting out an error signal by hooking up a test lamp or reader to it.

The problem with all this stuff is the sensors used put out very low voltage signals and in many cases it is only a fraction of 1 V so any corrosion on any wire can cause a fault as could any terminal where all but a few wires have broken.
Mowerman does not have the gear to read the outputs ( neither do I ) .
I keep some old dial voltmeters for making these readings ( best I can ) and bought a way too expensive LED test light that has never proved to be reliable.

bertsmobile1 said:

What both you & Super are missing is the fuel pump should pump up the system when the switch is turned ON way before he hits the Start Position
If you own a fuel injected car you have the same system.
When the key gets turned to the on position the fuel pump kicks in to pressurise the system.
This is what is not happening.
The pump relay is not firing up the pump unless the battery charger is on a very high setting and would be over voltage.

Depending upon which system he has either the ECU is duff, or the fuel pressure sensor ( if it has one ) is not sending a low pressure signal to the ECU so it fires up the pump.

So from here on Mowerman556 will have to go to the Kohler web site & download the service manual for his mower.
As he mentioned a "plug with about 40 pins" I will assume he has the 32 pin Bosch controller on his mower.
We have gone through all the easy stuff, now it will be a case of running the fuel pump control circuit diagnostics,
AS he has not mentioned an error code this would tend towards a problem with the ECU itself .

We do not know which engine & which injection system Mowerman has and even if he did there is very little I can do from here on.
The pump is in fact working and at some point the controls for the pump are working but the start up cycle is not unless the system gets an overwhelming voltage.

This normally would suggest a bad connection somewhere but he has done all of the jumping from the battery that he can so now we are left with the ECU & the pump relay, if the later is not part of the ECU or possibly the Fuel pressure sensor ( should it have one ).
According to how I interpret the manuals I have the unit should be showing a service warning if the pump , relay or pressure controller are bad and he is not getting one.
All that can be done now is to see if the ECU is putting out an error signal by hooking up a test lamp or reader to it.

The problem with all this stuff is the sensors used put out very low voltage signals and in many cases it is only a fraction of 1 V so any corrosion on any wire can cause a fault as could any terminal where all but a few wires have broken.
Mowerman does not have the gear to read the outputs ( neither do I ) .
I keep some old dial voltmeters for making these readings ( best I can ) and bought a way too expensive LED test light that has never proved to be reliable.

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Good observations and info. This is an a very interesting problem and troubleshooting thread. My experience with similar issues are with my '06 motorcycle that is fuel injected. While it is these are different machines, they shar a general design. The issues with my bike were traced to the main ground from the battery to the first connector(badly corroded). Adding extra grounds can be a big help, in my opinion, but doesn't help in this case. As you mentioned about a bad connection, that's worth exploring. It will take a patient and determined troubleshooter to track this problem down. It wouldn't surprise me that the root of the problem is very simple. I hope the OP will share the final solution.

Boit4852 said:

Good observations and info. This is an a very interesting problem and troubleshooting thread. My experience with similar issues are with my '06 motorcycle that is fuel injected. While it is these are different machines, they shar a general design. The issues with my bike were traced to the main ground from the battery to the first connector(badly corroded). Adding extra grounds can be a big help, in my opinion, but doesn't help in this case. As you mentioned about a bad connection, that's worth exploring. It will take a patient and determined troubleshooter to track this problem down. It wouldn't surprise me that the root of the problem is very simple. I hope the OP will share the final solution.

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Thanks to all of you for the assistance and measured response, as well as bearing with me as I sometimes take days to get back to the mower issue. Between near drought conditions here (outside of Detroit, MI) and the never ending to-do list, I don't work on the problem as diligently as I should. Again, appreciate all the inputs to date.

I'll also share that forward of the starter there are three black plastic relays. All of them have the same number on them. I can hear one of these relays "pick", as we used to say in the tech world, that is, the relay coil gets energized and the contact(s) are opening or closing (depending on configuration (NO or NC). I have NOT switched those relays around as yet. I will do that and see if it creates a change in symptoms, and report those findings back here.

Thank you for the tip on metering the battery voltage (it is brand new, one month old). When I turned in the core, the battery store tested and it registered 218 or so CCA. The new battery, tested before I left the store with it, registered 320 CCA. Note, it's the same brand and size of battery I have been using for years, this being the third or fourth in 5 years. The old one was installed in 2014.

Below are some photos of the external of the ECU box, or at least what I think is the ECU. It has what I referred to as a roughly 40 pin connector, which may be the Bosch 32 pin as mentioned. Interestingly, the serial number shown for the Engine on the Bosch box is NOT the same serial number as shown elsewhere. Back in the memory banks I seem to recall I had to have the dealer effect a repair, which involved a replacement ECU. I think that it was still under warranty its been so long ago. I have records in a file if this is important to look into.

There's also been some discussion of codes. I assume this is done with a reader of sorts, or by some sort of codes (blinks?) generated by the LED next to the start switch? This mower does not have any other gauges or readouts, no fuel gauges or anything, just the hour meter, so not sure how to accomplish any code diagnostics.

Thanks everyone, for the attention, and spurring me on to find this problem. Hopefully with all your help WE will solve this one together, before someone else has the same problem!!

ps... see the connector and module in the first photo. It's located on the right side of the engine, down low. What is it? Secondly I was surprised to see the insulation pulled back well over one inch (2.54 cm) on the middle conductor. Been like that since day one, unless there's been shrinkage on one insulation and not the others. I'll fix that as well.

As stated befoe, you will have to go to the Kohler web site & download the service manual for your engine.
The injected ones have E in front of the model name so are ECV ??? or ECH ???
The manual does have diagnosis methods both using the Kohler reader and just a test lamp counting blinks.
If you have a single bare wire on the plug, good chance that is the signal wire which some one pulled the insulation back so they can read it.
Individual sensors are generally tested disconnected but the ECU itself has to be powered up to be checked.

bertsmobile1 said:

As stated befoe, you will have to go to the Kohler web site & download the service manual for your engine.
The injected ones have E in front of the model name so are ECV ??? or ECH ???
The manual does have diagnosis methods both using the Kohler reader and just a test lamp counting blinks.
If you have a single bare wire on the plug, good chance that is the signal wire which some one pulled the insulation back so they can read it.
Individual sensors are generally tested disconnected but the ECU itself has to be powered up to be checked.

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@bertsmobile1 The mower is fuel injected, it is the Kohler CH745. I did get the Kohler engine manual, document number 24_690-01-EN.pdf online and downloaded it. I'll be going through the wiring and fuel prime operation, thanks!

@boit4852

thanks for the tip on the voltage check across the battery terminals. The battery is new this year, btw.

I'm using an analog VOM. On the 50 volt scale the meter pointed to 12VDC. Being a rather small meter I could not get any more accuracy. When I cranked the engine, the VOM reading did drop to 10VDC as you said it might. I thought that was interesting, and a step in the right direction toward resolution. I will check with local auto parts stores to see if they can test the starter motor for the mower, and go from there, as well as check more of the wiring, clean the connections again and etc.

mowerman556 said:

@boit4852

thanks for the tip on the voltage check across the battery terminals. The battery is new this year, btw.

I'm using an analog VOM. On the 50 volt scale the meter pointed to 12VDC. Being a rather small meter I could not get any more accuracy. When I cranked the engine, the VOM reading did drop to 10VDC as you said it might. I thought that was interesting, and a step in the right direction toward resolution. I will check with local auto parts stores to see if they can test the starter motor for the mower, and go from there, as well as check more of the wiring, clean the connections again and etc.

Click to expand...

take the battery and have it checked also

mowerman556 said:

@boit4852

thanks for the tip on the voltage check across the battery terminals. The battery is new this year, btw.

I'm using an analog VOM. On the 50 volt scale the meter pointed to 12VDC. Being a rather small meter I could not get any more accuracy. When I cranked the engine, the VOM reading did drop to 10VDC as you said it might. I thought that was interesting, and a step in the right direction toward resolution. I will check with local auto parts stores to see if they can test the starter motor for the mower, and go from there, as well as check more of the wiring, clean the connections again and etc.

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It comes back to people not having a proper understanding of basic electricity.
A battery stores ENERGY not volts not amps.
Volts & amps is how we measure the energy that a battery can provide so when you have a heavy Amps draw, the Volts will always go down.
I used to run a fleet of Rolls Royces hire cars and the voltage drop was so high the engine would not fire while it was cranking on the Electronic ignition models and these cars had massive batteries.
We had to retrain all the drivers how to start the cars and once they got it pat, no more flat batteries & burned starter motors.

However your problem appears to be a timing one as you previously mentioned the pump should prime when the ignition is turned on, BEFORE the engine cranks & the voltage drops.
SO the appropriate check would be voltage at battery ignition off vs ignition on
If there is a voltage drop of 0.5 V or more that points to a fault in the wiring applying an excessive load ( potential short )

Simular issue here. Mowed with it until I was done then had to use the bathroom. Pulled up to the front door and when I came back out no power to starting circuit. No fuel pump and no starter. I do not really carry all my tools with me so did the basic test that I could. My electrical tester indicated no power through the ignition. Went to store and picked up new ignition switch. Replaced it and still nothing. Searched more checking all relays and safety switches. Nothing I could find. Then thought maybe the solenoid on the starter. I jumped the starter with jumper cables and I got starter spinning but no gears to the flywheel. Tada found the problem. Called around and no one stocked the starter and it was priced at an astronomical price. $485.00 plus shipping. Went online and found one for $48.00 OE replacement. Ordered it and when it came in I installed it. I now have power to everything for a split second before the fuse blows. No what? Totally at a loss for what it could be. Then I remember I replaced the ignition switch. I reinstalled the switch and started right up. I bench tested the old starter and it was bad. So it turned out to be a bad solenoid that was causing all the power to not go to the other parts.

@BlazNT thanks for sharing your experience. I've not been on the forum for a while due to any number of more pressing personal and family matters. So, I've been starting the mower with the aid of the battery charger all summer and fall. I'll dig in to the starter solenoid being the problem. Out of curiosity... did you attempt to start the mower with a battery charger like I've been doing, and did it start in that situation? Thanks!

mowerman556 said:

@BlazNT thanks for sharing your experience. I've not been on the forum for a while due to any number of more pressing personal and family matters. So, I've been starting the mower with the aid of the battery charger all summer and fall. I'll dig in to the starter solenoid being the problem. Out of curiosity... did you attempt to start the mower with a battery charger like I've been doing, and did it start in that situation? Thanks!

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I did not have a battery charger with me at the time. When I was finally around one I had already figured out the problem. So I never got to test it that way. While you are down there tighten the ground bolt.

@BlazNT Thanks for the feedback. I already checked the wiring and the ground bolt, and even paralleled a second ground wire from the battery to the negative lug, and also tried several other grounding locations on the frame and engine. No change.

Again, the situation with my mower may be a bit different than what you experienced with yours. When I turn the key, the mower does not get the fuel pump "prime" that lasts for 5-6 seconds. Thats the buzzing you hear when you flip the key to "ON", and before you turn it to the start position to crank the engine.

Without that "prime" cycle, the engine will crank and crank and crank, but will not start. Once I put a battery charger on the battery (which is new this year), you can hear the fuel pump "prime" cycle when the key is turned on, and after that cycle, the mower starts as normal. I've been starting it that way, with the aid of a battery charger all this mowing season since the problem cropped up in the spring.

@John Fitzgerald not for me. EFI is superior to carburetors all day long, and, the issue at hand that I am experiencing has nothing to do with fuel delivery, but rather a fuel "prime" issue.

Can we not change the topic and theme of the thread, please? Thanks in advance!

Ever have the starter bench checked?
Replace solenoid?
Replace fuel pump relay?

I had the same issue with my Lazer Z HP with the 23HP Kawi FH series engine. The starter was shot and drawing too hard. I replaced it and the problem was resolved. It wasn't cheap, on the order of $200.

GrassBarber said:

Ever have the starter bench checked?
Replace solenoid?
Replace fuel pump relay?

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Hi GrassBarber, thanks for the tips. I'd not done those things. Being in the depths of winter I've not been much interested to get out to the barn to work on the mower. Breaking my wrist in January didn't help matters any either, LOL!

Another month or so and I will start back into it, and check those items. When I do I'll be sure to get back to you and let you know what I find.

Thanks again!

Darryl G said:

I had the same issue with my Lazer Z HP with the 23HP Kawi FH series engine. The starter was shot and drawing too hard. I replaced it and the problem was resolved. It wasn't cheap, on the order of $200.

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Thanks Darryl G. Before you changed the starter did you also experience that the mower would start if you connected a battery charger to it, in order to get the prime?

In my case the mower cranks and cranks and cranks (new battery last June) and sounds normal while cranking but it will not fire, because it does not get the initial fuel "prime" when the key is turned (the "buzz" you hear for several seconds when the key is turned to the on position).

If I hook up a battery charger to the battery and turn the key on I do get the prime, and then the mower starts normally. The starter motor is not in play at that point (during the prime), so not sure how it could be the starter?

Once the mower starts it runs just fine. I just don't shut the mower off until I'm done and parked back in the barn, as it will not re-fire (hot or cold) unless the charger is connected to the battery again. Used it that way all last summer, LOL!


Thanks!

Mine would but not fast enough to fire and would drain the battery quickly. If I hooked it up to my charger and put on the 55 amp start setting it would crank fast enough to fire up.

mowerman556 said:

Thanks Darryl G. Before you changed the starter did you also experience that the mower would start if you connected a battery charger to it, in order to get the prime?

In my case the mower cranks and cranks and cranks (new battery last June) and sounds normal while cranking but it will not fire, because it does not get the initial fuel "prime" when the key is turned (the "buzz" you hear for several seconds when the key is turned to the on position).

If I hook up a battery charger to the battery and turn the key on I do get the prime, and then the mower starts normally. The starter motor is not in play at that point (during the prime), so not sure how it could be the starter?

Once the mower starts it runs just fine. I just don't shut the mower off until I'm done and parked back in the barn, as it will not re-fire (hot or cold) unless the charger is connected to the battery again. Used it that way all last summer, LOL!


Thanks!

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If you don't mind, what charger are you using? Is it the type that doubles as jump starter?

Yeah, 2/10/55 amp settings.

Boit4852 said:

If you don't mind, what charger are you using? Is it the type that doubles as jump starter?

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Battery charger is made by Century, and as Darryl G said, has the 2 / 10 / and 55 a. start settings. I use it on the 55a setting to start the mower. I think I tried the 10a setting once last summer. It did not start immediately (the fuel pump did not prime) but after letting it set a few minutes the mower did start with the 10a setting.

Rather than mess around, I just leave it on the 55a setting and start the mower that way.

Thanks for the inquiry!

The engine should not need such high amps for it to start. Sorry to state the obvious. From this point, The correct stock battery should provide enough amps. Tracking down why will lead to a solution. I was thinking a bad relay since a relay requires very low amperage to trigger and from there, high amps flow to the end device, whether it's a starter motor or some other high amp draw device. It's not unheard that there was a mistake made by an hourly paid employee doing the assembly. I experienced this on a Honda walk-behind mower a few years ago. If it was me, I'd get the factory repair manual and check that all wiring is correct according to the schematic.

Did you ever replace the starter relay and starter?

I still have money on those being the fix. Damned if i would screw around with a charger when this can easily be fixed with a starter replacement.