Left Cylinder Stops Firing Intermittently

Greetings everyone!

I am having a problem with my Lesco/Cub Cadet Tank ZTR. It has the Kawasaki FH680V, 23 HP engine. A few months ago I pressure washed the mower, including around the engine. This is something that I do every few months to keep things clean. I use fairly low pressure and am always careful what and where I spray. After completing the cleaning I cranked her back up, let it run for a few minutes and put it up. The next day I cranked it up to move my boat and utility around the property. Running at WOT (wide open throttle) suddenly the RPM dropped, sill running smooth but dropped from 3,600 RPM down to 2,500. After a 20-30 seconds it came back to life and was fine. This problem continued every minute or so. It felt like one cylinder just died...but with some occasional popping and black smoke (obviously from the unburned fuel).

Yesterday I cranked it up and the same problem exists. I checked the carb and it was perfectly clean. After that I sprayed starter fluid into the intake when it would drop to one cylinder (still hoping for a fuel problem). No change in RPM. So, not fuel related.

While running I pulled both plug wires. When the right side was pulled the engine begin to sputter and die. When the left side was pulled the RPM dropped appropriately but continued to run smoothly. OK...left side has a problem. I checked and swapped plugs. No Joy. I then swapped both coils (hoping the problem would swap sides). Still no joy. The problem remained on the left side!

From the repair manual I pulled the coil winding resistance chart that tests for resistance using an ohm meter (PDF attached). My A to C readings were within specs. My A to B reading for both coils were just barely within specs. The C to B readings were way below specs. This was true on both coils. I was hoping for one obvious bad coil but both have almost identical readings.

I am at a loss as to what to try next. Any suggestions or guidance would be sincerely appreciated! Thanks!

Link for Coil Test Results, PDF:
https://www.dropbox.com/s/z9muqbl9dr8sv24/Kawasaki%20Coil%20Test001.pdf?dl=0

What you describe I have seen several times on Briggs, Kohler, and Kawasaki engines. It seems after the engine gets wet, either from washing, or high humidity the modules draw moisture and will cause the symptoms you describe. And normally I find it will effect both modules not just one. I would also bet that if you inspected the epoxy on the modules will have cracks in it, especially around the kill wire terminal. Most likely you will need to replace both modules to repair the mower.

I would also bet if you disconnected on spark plug, and it doesn't matter which one, and try to start the mower it won't start.

ILENGINE said:

What you describe I have seen several times on Briggs, Kohler, and Kawasaki engines. It seems after the engine gets wet, either from washing, or high humidity the modules draw moisture and will cause the symptoms you describe. And normally I find it will effect both modules not just one. I would also bet that if you inspected the epoxy on the modules will have cracks in it, especially around the kill wire terminal. Most likely you will need to replace both modules to repair the mower.

I would also bet if you disconnected on spark plug, and it doesn't matter which one, and try to start the mower it won't start.

Click to expand...

Thanks for the reply. Both coils have no obvious cracks...but I have not checked closely around the kill terminal. We live on the Gulf Coast and on the water...our humidity is always high! It is possible that a dual coil replacement is the cure. Thanks again!

Remove both valve covers and compare them while rotating the flywheel by hand.
You will likely spot the problem.

Compare the valves and rockers, etc.....
Not the valve covers........

You may have a loose valve seat, or the like....

Fish said:

You may have a loose valve seat, or the like....

Click to expand...

Thanks. I went ahead an ordered two new coils since some of my ohm readings were off the mark (plus they were severely rusted). However, I will pull the valve covers and take a look...just in case!

the coils have a Hall Effect trigger chip in them that replaces the old points.
Because of this you need quite specific meters to check them with.
A Radio Shack multimeter is just not good enough.
So unless you are using a multimeter that cost well over $ 100 ohm readings mean very little.

Easiest way to check what Illengine said is to pull the cover off the air box & put some sponge in there to stop water entering the carb.
Start the engine then spray water into the top of the engine.
If all is good it should run as normal .
If it splutters then you know something is shorting out when wet.
Mower engines should run under water just so long as the carb is not sucking water.

well, the swapping of them was a great diagnostic move.
And since the engine behaved exactly the same after the swap tells me that the coils are not involved...

Pulling the valve covers is easy to do, and will likely reveal your problem.
As you revolve the flywheel by hand, look at the action of the rocker arms, and how they engage the valves.
Look at the valve heights when the rockers are not touching them, the stems should all return to the same height.
It is hard to predict what you will see, but I think you will likely see something.
If not, just put the covers back on....
You have wasted no money at all, and have only wasted 10 minutes of time.

The price of 2 coils, well........