perplexing LX188 ignition issue

[SteveA]

Yesterday, when I ran my mower, there was a loss of power when engaging the PTO where it appeared that the engine was running on 1 cylinder. Adjusted the (new) PTO clutch, and did a compression test on both cylinders (+/-200lbs).
I noticed the left cylinder plug was wet and most likely not firing. Per the shop manual, I tested both ignition coils and the pulsers for resistance and everything was within specs. I also tested both positive primary leads (yellow/white wires)to the ignitions coils and both had battery power.
I then cranked the engine with the right cylinder plug out and grounded to the block and had good spark. Did the same on the left side and no spark. Switched coils and plugs and still only the right side would spark. Bad igniter?? Any suggestions would be appreciated. Thanks.

 

[BBO]

Yesterday, when I ran my mower, there was a loss of power when engaging the PTO where it appeared that the engine was running on 1 cylinder. Adjusted the (new) PTO clutch, and did a compression test on both cylinders (+/-200lbs).
I noticed the left cylinder plug was wet and most likely not firing. Per the shop manual, I tested both ignition coils and the pulsers for resistance and everything was within specs. I also tested both positive primary leads (yellow/white wires)to the ignitions coils and both had battery power.
I then cranked the engine with the right cylinder plug out and grounded to the block and had good spark. Did the same on the left side and no spark. Switched coils and plugs and still only the right side would spark. Bad igniter?? Any suggestions would be appreciated. Thanks.

Check the battery voltage when running, then again, after you engage the PTO.

 

[SteveA]

Check the battery voltage when running, then again, after you engage the PTO.

OK will do. Are you suspecting a charging system issue?

 

[BBO]

OK will do. Are you suspecting a charging system issue?

I would just rule out voltage drop from a bad battery, voltage regulator or a bad wiring harness connector.
Does the alternator light come on when the switch is turned on?

I 1st thought the PTO clutch might be almost shorted and bad, but you mention the clutch is new.
Did you check the ohms in the clutch before you installed it?

The stator should be producing about 26VAC on the 2 outside wires at the VR connector.
Then the battery should be about 13.5-14.5 VDC when running.
If the clutch solenoid is sucking this way down it could be several things.

 

[SteveA]

Thanks for the replies. I will check the items you listed. BTW, the battery is also new this season. I did notice that when I initially start the engine, it runs rough and the alternator light would come on briefly and then go off as the engine warmed and smoothed out. I never pre-tested the new OEM clutch prior to installation but will do so.
Last year I struggled with sloppy drive belt issues. The mower is a 1992 and I have owned it since new. Over the years I have changed out various drive pulleys and idlers, and the arm as they wore out but the engine sheave and tranny sheave were original. This spring I changed out everything (after the belt finally shredded)underneath and the belt tracks much smoother. Since I had to pull the original PTO clutch to change the sheave, I decided to replace it. BTW, with the PTO off, should the PTO pulley turn freely by hand or is there a brake? With the mower deck installed, the blades turn off as usual. With the mower belt off the PTO pulley, I cannot turn the pulley by hand. I did adjust the gap to .020 with the same results.

 

[BBO]

..I did notice that when I initially start the engine, it runs rough and the alternator light would come on briefly and then go off as the engine warmed and smoothed out... BTW, with the PTO off, should the PTO pulley turn freely by hand or is there a brake?

Those clutches are a bit weird, the external pulley stays in place as if it has a brake, the internal part is what free wheels.

On the drive train belt, make sure the center tensioner/idler and pivot bushings are good, which keep the idler straight.
This is held by a single bolt up top just in front of the gas tank. I have rebuilt 2 of these with new bushings.
I suppose you have already replaced the pulley and fan over the transmission using the waffle washer.

The VR plug I am suspecting is a common problem. It has the circuit for the alternator light in it, and also the stator supply and the battery charging DC supply. They heat up and melt part of the white nylon connector and you may have to replace the plug and all 6 pins.
This is a bad one..

 

[SteveA]

After going through the ignition system with a process of elimination, the only component left was the ignition module. I changed it out and now the engine runs like new. Those FD501V's are tempermental buggers but when running right, tough to beat. Thanks for your help. BTW, I did change out the VR plug (melted) several years ago when the regulator crapped out. I pulled it and found some evidence of heat build up short of melting. Had a spare VR kicking around so I changed it out along with the spade connector (I had left from the last go round)for the charging wire. The nylon plug was OK.