LX178 no spark

[jeepcoma]

After running beautifully all summer (after replacing the stock mechanical fuel pump with an electric), my LX178 (with engine Kawasaki FD440V) one day simply refused to start. The engine cranks and cranks but refuses to start. I can smell gas, and the plugs are wet when I remove them, so it's getting fuel.

Tested so far:

PTO switch; if PTO is on, engine won't crank, so this is fine
Parking brake switch; if brake is off, engine won't crank, so this is fine
seat switch; doesn't matter when in park
Checked fuses, both main 15 amp fuses were good

I took my trusty induction timing light to check for spark under standard conditions with plugs installed. Neither cylinder is firing, so while it could be a coil problem, I suspect not since it was working perfectly when I parked it. Both failing at the same time seems unlikely. I did once see a random firing; it was very erratic, rapid, and not at all in synch with the cranking of the engine. I have twice gotten a huge explosion out the muffler after I stop cranking (though I wasn't checking for spark at the time). It seems like if it does spark at all, it's not at the correct time.

I went through all the wiring that's visible (did not remove radiator to check the pulser coils yet), everything looks good, no obvious signs of mice chewing or rubbing or melting. All the connectors were good and tight, no loose pins that I could see, and I cleaned everything up with WD-40 in case there was moisture somewhere.

I'm thinking of three possibilities at this point:

Ignition module (or igniter as it's called by JD). I don't know how to test this, other than by looking at it and the connectors seem good and there's no corrosion or anything bad looking (I removed the side cover and looked in, though I couldn't figure out how to pull out the PCB without breaking it). I read that some shops can plug this in and test it, but I'm not sure if that's true. Would a JD dealer be able to test? I've also read about shade-tree mechanics swapping in modules from other applications (one mentioned using a points-to-electronic conversion module, or from some Ford trucks). That would be cool and inexpensive, but I don't know what wires would go where. The service manual says to test by replacing with a known good module, they are $$ brand new from JD! Does anyone have a spare they'd sell? I think I should be able to simulate a signal from the pulser coils by applying 12v to the correct wires, and then when I remove the 12v I should see a spark? I can also test each coil this way.

Pulser coils. If they aren't getting signal from the flywheel or aren't sending to the igniter, the igniter can't send current to the coils. Still though it seems unlikely they would both fail at once, but perhaps something with the wiring. Do I need to remove the radiator to check these? Or can I hook up a multimeter and test for voltage with the engine cranking?

Ignition relay. There are a few wires that go to the igniter and the coils, pink, yellow/white, and orange/white. The orange/white goes to the igniter, if there's no signal there I don't think the igniter gets power. Also looking at the wiring diagram, if there is a problem at X6 connector both coils and the igniter won't get power, so I will definitely check that out. I could also try to bypass the ignition module by wiring the battery positive to the yellow/white wires on the coils and the orange/white wire in the igniter.

Any other "quick fixes" or things I'm overlooking? I'd really like to get this running since the leaves are starting to fall in earnest!

 

[Shimon]

First, I would check to see if the pink wire coming off the circuit board connector X4 has voltage with the key on. This is the output from the ignition relay which provides power to the ignition coils and module. The grounds to the coils are provided by the ignition module which completes the circuit. If no power on the pink then it could be a safety switch or ignition relay or some other issues...but do this test first and then we can tackle the next procedures.

If the pink wire is good then you can try to test one of the coils by providing your own ground to the coil. Hold one of the spark plug wires coming off the coil (unplugged from spark plug near a ground so you can see a spark if it develops) and apply and then release a ground to the coil. If this works then your ignition module is bad.

Like you said, it would be odd (but not impossible) for both sides to go out at the same time so most likely it's a common source problem: ignition relay, ignition module or wiring to these items.

 

[rayikeo2]

Take a visual check of all wires under the hood near the starter for mouse chewed wires. Going into fall a mouse could have chewed a wire causing this problem. It happened to me. check near and around the starter and under the battery area too. If you find any evidence of chewing on any wires look for breaks and splice them back togather if broken. Sometimes simple things can cause major problems.

 

[jeepcoma]

Turns out I'm just plain ignorant about how this thing is supposed to run, mixed with some dumb luck. It's been running on one cylinder the entire time I've had it!

I double-checked all the wiring, still no kinks, bites, melts, rubs, or frays. Then I took the multimeter and started testing everything, and it looked like the correct signals were making it all the way to both of the ignition coils. I thought that strange but took an old motorcycle coil I had lying around, disconnected the right side coil and wires, and wired the new one in. It's a dual-terminal coil too so I was able to hold a plug to the block and visually see one outside the engine while the other plug was installed. It fired right up!

Strange it runs so well one just one cylinder, it actually ran better with this spare coil I had than it ever has before; it started up with the throttle completely down (I was just checking for spark first) and it never did idle correctly before (now I know why, since it was on one cylinder). It also had some trouble going up hills while mowing. I chalked both conditions up to bad fueling since it was sitting for so long, now I guess I know better. Could be why the previous owner junked it too, if they couldn't figure out what was wrong with it. Still, it's never had any trouble starting, was nice and smooth, no visible shaking or anything, only a dirty plug.

I couldn't actually get the engine to run using the left side. I'm not sure why, but given that I was just micky mousing things together with odds and ends I'm hoping it's not actually a serious problem with the left cylinder. I did a compression test and both sides were idential (100 psi cranking with the other plug removed and throttle wide open). I was afraid I'd find no pressure on the left side but it matched the right, so I'm hoping just getting a new coil will fix it.

Ironically the reason I had a spare motorycycle coil is that one coil went bad so I had one good left over from the pair. The brand was also Denso (same as in the FD440V). Besides possibly finding a cheaper alternative perhaps there is a more reliable or "upgraded" coil I could swap in? I took the coil over to autozone to find some universal replacement but they were no help, so it looks like I'm stuck with online. I can find two new shipped for about $75, which isn't terrible (NAPA has them for $50 each), but there must be some cheapo alternatives.