John Deere 245 with FC420V - Backfires when cranking, no longer starts

[draker]

I picked up this JD 245 with a blown 14HP FC420V. The motor had thrown a rod and wrecked the case, piston and everything inside.

I bought a spare FC420V on ebay that was missing the flywheel, stator, coil, ignition module and carb. I swapped everything from my motor over to the new motor and cranked it over. It started pretty easy, no smoke, sounded great! I let it warm up and then shut it down to finish installing the rest of heat shields and hood.

The next time I tried starting it, it was a little harder to start. Then it got progressively harder to start, and it started to backfire out of the exhaust and carb. Massive gunshot type backfires. I did manage to get it running and mow a 1/2 acre lot. It ran fantastic! Just hard to start.. and now it won't start at all.

After doing a bit of research this is what I've done so far:

• I found it's common for the key to sheer and the timing to be off. So I pulled the flywheel to make sure the key didn't get pushed down when I installed it. Its in its place as expected.
• Set the valves to .006 when cold.
• Checked the compression and it's right around 120psi after a few cranks.
• Spun the pushrods around to make sure they weren't bent, they look fine.
• Checked spark, it seems okay. I mean, it's there. Not sure how strong of a spark it is.
• Cleaned the coil pickup and flywheel magnet
• Swapped spark plugs
• Checked coil resistance, both sides of the coil were SLIGHTLY out of spec, low. I confirmed with two Ohm meters.
• I couldn't determine if the ignition module was bad. The service manual is kind of fuzzy how to check this.
• Pulled the carb and cleaned and inspected it. It wasn't dirty at all.

I am wondering, where there different flywheels for the FC420V that might be throwing the timing out?
Could a bad coil cause these backfires?
How do I test the ignition module? I'd rather not just throw parts at it, if I can avoid it.

 

[bertsmobile1]

Already answered most of this on your other post
1) all FC engines use the same flywheel
2) all FC engines use the same trigger ( igniter )
3) all FC engines use the same coil

The only difference ignition wise is some have an oil level cut out switch & some don't.

The warnings about chip damage previously mentioned still apply.
There is a big difference between a $ 200 Fluke meter and a $ 20 Harbour Freight meter & a $2 Walmart one.
A cheap meter puts too much current down the test leads & can fry the hall effect chip.
Always ask the dealer to test a module before you leave the shop because once you walk out the door the units are not refundable.
This even applies to me.
Once I walk out of the wholesalers warehouse the warranty on electrical items evaporates
Double check the valve timing and the spark plug gap.
A small gap advances the spark, & a wide gap retards it.
Same with the coil gap, too close advances the spark & too far away retards it.

If everything checks out mechanically then move the coil further away.
As it get further away the spark get weaker so the gap may need to be reduced.
Also triple check the coil.
It is direction sensitive so if it is on upside down you can get all sorts of crazy results.

 

[draker]

Already answered most of this on your other post
1) all FC engines use the same flywheel
2) all FC engines use the same trigger ( igniter )
3) all FC engines use the same coil

The only difference ignition wise is some have an oil level cut out switch & some don't.

The warnings about chip damage previously mentioned still apply.
There is a big difference between a $ 200 Fluke meter and a $ 20 Harbour Freight meter & a $2 Walmart one.
A cheap meter puts too much current down the test leads & can fry the hall effect chip.
Always ask the dealer to test a module before you leave the shop because once you walk out the door the units are not refundable.
This even applies to me.
Once I walk out of the wholesalers warehouse the warranty on electrical items evaporates
Double check the valve timing and the spark plug gap.
A small gap advances the spark, & a wide gap retards it.
Same with the coil gap, too close advances the spark & too far away retards it.

If everything checks out mechanically then move the coil further away.
As it get further away the spark get weaker so the gap may need to be reduced.
Also triple check the coil.
It is direction sensitive so if it is on upside down you can get all sorts of crazy results.

Thanks for taking the time to reply!

Mechanically everything looked fine. I rotated the engine with the plug out, looked at the valve operation. Everything seems to be working as expected. I'll check everything again and the other things you mentioned. I set the coil gap with a business card, but I've got the factory service manual so I'll go back and set it to spec.

Regarding testing the ignition module, what is the actual procedure? I couldn't understand what the service manual was trying to tell me.

Do you think the coil reading being low on both sides would cause erratic timing or just poor spark conditions? I think one side was about 1500k low and the other side was about 2 ohms low.

I am plagued with cheap meters.. I'll try to source a better one.

 

[bertsmobile1]

Thanks for taking the time to reply!

Mechanically everything looked fine. I rotated the engine with the plug out, looked at the valve operation. Everything seems to be working as expected. I'll check everything again and the other things you mentioned. I set the coil gap with a business card, but I've got the factory service manual so I'll go back and set it to spec.

Regarding testing the ignition module, what is the actual procedure? I couldn't understand what the service manual was trying to tell me.

Do you think the coil reading being low on both sides would cause erratic timing or just poor spark conditions? I think one side was about 1500k low and the other side was about 2 ohms low.

I am plagued with cheap meters.. I'll try to source a better one.

The chip should be about $ 30 .
Get one & ask the dealer to check it then DON'T TOUCH it.
Or take your modules to an authorised dealer & ask them to test them.
Double check the coil is not on upside down.
Most are marked "engine side" and many times the HT lead is pointing the wrong way round.

The module is just a set of electronic points which makes & brakes a ground contact

 

[draker]

The chip should be about $ 30 .
Get one & ask the dealer to check it then DON'T TOUCH it.
Or take your modules to an authorised dealer & ask them to test them.
Double check the coil is not on upside down.
Most are marked "engine side" and many times the HT lead is pointing the wrong way round.

The module is just a set of electronic points which makes & brakes a ground contact

I actually found a good meter, and tested the module. I got no continuity in either direction using the attached diagnostic.



The replacement part is $104. I'm going to take a chance on an aftermarket module for a fraction of the price. I know... I know. Could be trash also. If I can get it started, then I'll know was the issue. Happy to pony up the case if can confirm it was defective.

 

[bertsmobile1]

Same story.
Check to see if the after market suppliers do a module.
If they do then get one from a workshop and ask them to test it.-
Before you fit it, check the wires that connect it to the mower for battery voltage.
The wire from the coil should show a MILLI - Volt reading as the magnets pass the coil and it should go + through to - ( or visa versa ).
As for that price WOW the cost of the chip is less than $1.
The printed card it is shipped with costs more than the chip.

The manual is confusing because there is the original chip and the newer chip so the different readings are for the chips of that particular shape.
Also note that the module grounds so if the ground is bad then the module can not work properly.

What is happening is the cylinder is not firing so your muffler is filling with unburned fuel.
The first time the cylinder does fire, the exhaust ignited the unburned fuel in the muffler causing the backfire.

a bit left field , but try starting the engine will starting fluid then see if it will keep running while you give it short small shots down the carb.
Some times a dodgy fuel shut off solenoid will cause this to happen.
Also do you have the low oil switch fitted ?
A faulty low oil switch will also cause similar symptoms.

 

[draker]

Same story.
Check to see if the after market suppliers do a module.
If they do then get one from a workshop and ask them to test it.-
Before you fit it, check the wires that connect it to the mower for battery voltage.
The wire from the coil should show a MILLI - Volt reading as the magnets pass the coil and it should go + through to - ( or visa versa ).
As for that price WOW the cost of the chip is less than $1.
The printed card it is shipped with costs more than the chip.

The manual is confusing because there is the original chip and the newer chip so the different readings are for the chips of that particular shape.
Also note that the module grounds so if the ground is bad then the module can not work properly.

What is happening is the cylinder is not firing so your muffler is filling with unburned fuel.
The first time the cylinder does fire, the exhaust ignited the unburned fuel in the muffler causing the backfire.

a bit left field , but try starting the engine will starting fluid then see if it will keep running while you give it short small shots down the carb.
Some times a dodgy fuel shut off solenoid will cause this to happen.
Also do you have the low oil switch fitted ?
A faulty low oil switch will also cause similar symptoms.

Started checking this stuff tonight. Pulled it all apart again to confirm the coil direction. Looked at the fuel shutoff solenoid. I believe it does have a low oil pressure switch. At least there is a light on the dash.

Confirmed the spark gap was correct. Tried starting fluid in the carb.

But good news.. I reinstalled the coil but set the gap with a feeler gauge to .3mm. Turned over the motor and it fired right up!!

As I mentioned previously I had set the gap with a business card like many have referenced. Well that was smaller than when I initially installed the coil.. but it was still at least .6mm gap.

My recommendation... don't use a business card!! Set it to spec. I spent hours and hours on this.. and it was just a gap issue.

You nailed it in one of your first replies. Spot on! Thank your for the assistance. I was getting to the throw parts at it stage.

Hope this helps the next guy for years to come.

 

[bertsmobile1]

Started checking this stuff tonight. Pulled it all apart again to confirm the coil direction. Looked at the fuel shutoff solenoid. I believe it does have a low oil pressure switch. At least there is a light on the dash.

Confirmed the spark gap was correct. Tried starting fluid in the carb.

But good news.. I reinstalled the coil but set the gap with a feeler gauge to .3mm. Turned over the motor and it fired right up!!

As I mentioned previously I had set the gap with a business card like many have referenced. Well that was smaller than when I initially installed the coil.. but it was still at least .6mm gap.

My recommendation... don't use a business card!! Set it to spec. I spent hours and hours on this.. and it was just a gap issue.

You nailed it in one of your first replies. Spot on! Thank your for the assistance. I was getting to the throw parts at it stage.

Hope this helps the next guy for years to come.

Thanks for getting back & closing the thread
Enjoy your mowing and don't forget to wear your deer stalker cap ( Shirlock Home Award ) with pride.