One cylinder intermittently not firing

[MBDiagMan]

I hope you guys won't mind commenting on the problem I'm having with my John Deere Gator 825i. I have a reasonable amount of experience troubleshooting EFI car and truck engines, but this one is a little different.

This buggy has an 825cc. Chery, 3 cylinder EFI engine. It has individual coils on the end of the engine. There is no indication of a code being set, but although my scanner will connect to the connector under the dash, it turns out that John Deere has proprietary software so my scanner won't work.

One month after the warranty expired, it developed a missing cylinder. I pulled the plugs and found the center one fouled. I cleaned it and the miss went away temporarily.

I then used a stethoscope while it was missing and could hear all the injectors clicking normally. Although in my fifty years of messing with engines, I've only seen one spark plug that was actually bad, I swapped the number one and two spark plugs and the foul stayed with the center cylinder.

I then swapped the coils between number one and the center cylinder and gave it a hard run. After it warmed up real good it began missing. I brought it back to let it cool before pulling the plugs and thought sure that I would see the number one plug fouled instead. It had been intermittently running well, and what I found was traces that the center cylinder had tried to foul, but couldn't confirm.

I plan on giving it another hard run to see if I can get a consistent foul so that I can confirm which cylinder is now fouling, but at this point it appears that the center cylinder is the culprit even with the swapped coil, but remember, I have not totally confirmed this.

Also, when running it at speed, when the miss develops, I get a popping and snapping from the exhaust, which seems to indicate that unburned fuel is making it into the exhaust and causing this.

Any experience with a similar situation?

Thanks for sharing your savvy and experience.

 

[Leejohn]

As I was reading your post the 1st thing that came in my mind was bad valve guides in that cyl.

 

[rsallen]

What kind of fouling? Oily or lamp black soot.

You could do a compression test for giggles.
But I think your next stop is fuel pressure, then think about #2 injector.

 

[Egon]

Consider new wires to the effected cylinder?

 

[MBDiagMan]

Thanks for the replies!

The engine is near new and I just can't imagine valve guide trouble. Since it is not an oily foul, it seems to rule it out even more. When fouled it looks black, but not sooty black. More of a wet black.

There is no mechanical connection for checking fuel pressure. I expect that it is tested through the ALDL, but as I said I don't have the proper software.

I too suspect the ignition wire and want to run it some more until I get a definite foul before putting a wire on it.

Since it is popping in the exhaust when this happens, it seems that it is putting raw fuel through that cylinder and popping in the hot exhaust.

My wife and I are leaving Saturday for a short vacation. I probably won't get a chance to run it anymore before the end of next week. I will report back then.

Thanks again. I was hoping someone had seen something like this before. I still tend to believe that the problem is on the ignition side, but intermittents always seem to make me think things that don't turn out to be correct.

Any further comments are welcome and very much appreciated.

 

[rsallen]

But but but, didn't you say you had individual coils per cyl.? And that you've already swapped them around with no change?
And yep, wet but no oil means fuel.

 

[Beltman60]

If its a newer engine do you have a warranty?

 

[tcartwri]

valve guides. one or both of the valves on that cyl are hanging open intermittently.

 

[rsallen]

Tight valve guides?!!!!!
Now after how many hours?
You can't be serious.

 

[tcartwri]

Tight valve guides?!!!!!
Now after how many hours?
You can't be serious.

Completely.

 

[rsallen]

Okay.
Let's put 50 hours on the machine. Why would it now start with sticking guides instead of doing so in the first or second run-in period? There's more play in them now than there ever has been.
I'd buy into a broken or weak valve springs if that engine make had a history of putting garbage materials into their product, but sticking valve guides well after the break-in period.....nah, you're just pulling my chain. Right?

 

[tcartwri]

Okay.
Let's put 50 hours on the machine. Why would it now start with sticking guides instead of doing so in the first or second run-in period? There's more play in them now than there ever has been.
I'd buy into a broken or weak valve springs if that engine make had a history of putting garbage materials into their product, but sticking valve guides well after the break-in period.....nah, you're just pulling my chain. Right?

Mine did it at ~250 hours. The guides are pressed into very cheaply cast aluminum heads, and they come loose.

 

[rsallen]

Then you were also sucking oil like crazy?

 

[MBDiagMan]

The engine has less than fifty hours, but was out of warranty by one week when the problem showed itself. Yes I have swapped coils, but have not run it enough to CONFIRM that the problem stayed in the same cylinder.

On another forum, someone familiar with this engine said that I should do a compression check when cold and again when hot. He thought that the spitting and popping in the exhaust after warm up was due to a valve too tight. I am not certain that this is happening only after warm up, but it might very well be. If he is correct with this hunch, I don't want to run it very much for fear of burning a valve. He also said that the valves are a pain to adjust since it is done with shims.

Remember, this is an intermittent problem.

I want to thank everyone a BUUuunnch for their replies and thoughts. I am about to take a little short vacation with my wife and it will probably be late next week before I get back to this.

 

[tcartwri]

Then you were also sucking oil like crazy?

Nope. Very little oil in the top end of these motors.

 

[buickanddeere]

Failing or weak valve spring is what I suspect he's thinking. Either valve spring or a air, oil or coolant leak.

 

[rsallen]

Hmmm,
So could you salvage the head with some over sized guides? Or was it just scrap and having to renew the head?

 

[clemenda]

Sounds like a bad coil pack