PO300 Random Misfire

[MGregoir]

I couldn't tell you what they did, I only briefly spoke with the service writer. I do know that I have had really good luck with this dealer diagnosing stuff and fixing it right in one try without a bunch of [censored] before so I won't question it too much.

If the part wasn't over $300 I would have replaced it myself on a hunch, but that's a lot of money to throw at a guess.

 

[calvin1]

Originally Posted By: MGregoir
I couldn't tell you what they did, I only briefly spoke with the service writer. I do know that I have had really good luck with this dealer diagnosing stuff and fixing it right in one try without a bunch of [censored] before so I won't question it too much.

If the part wasn't over $300 I would have replaced it myself on a hunch, but that's a lot of money to throw at a guess.


Ok, I hope it takes care of the problem. It just struck me as odd because another automaker's troubleshooting chart for this code has you doing a lot of checking for intake and vacuum leaks and nothing about the ignition module.

 

[highmilegeguy]

I'm surprised too!!

Ignition control modules are usually 100% functional or dead. I can't remember seeing one with intermittant failure.

Needless to say I'm suspicious that the fault wasn't some simple item with a money making cover story about a more serious component failure.

 

[MGregoir]

It is not uncommon for them to go in GM vehicles of this vintage and cause a P0300 code. It's happened before with this car.

I read the work order, they tested fuel pressure and checked for leaks, tested all of the wires and coils, then replaced the module and it fixed the problem.

It must have been marginal because it is definitely running a little smoother than it was when it was functioning. The mechanic figured that something in it may have shorted out, causing carbon tracks and the burned ceramic on the plug I saw.

I am glad I wasn't entirely on the wrong track.

 

[GMBoy]

Originally Posted By: MGregoir
The mechanic figured that something in it may have shorted out, causing carbon tracks and the burned ceramic on the plug I saw.


The only way carbon will track on the plug is due to bad wires. The wires were not seated fully or faulty...the resistance on that wire was probably very high leaving the energy from the coil not much choice where to go. That causes stress on the ignition system. Glad you're all fixed.

 

[mechtech2]

Plugs can carbon track for all sorts of reasons other than bad wires.
How about a casting flaw, or a crack from being dropped? Water. And a bunch of other reasons.

 

[MGregoir]

The plug showed signs of extreme heat (browning) around the ceramic that the others did not, and on the tower for that plug on the coil it showed signs of arcing. The plug wire was a tight fit however and the resistance/continuity tested fine.

Who knows, but it runs for now.