300M misfire code P0302 -> no coil codes, no injector codes?

Also, if its a plugged injector or mechanically failed injector (not an electrical fault) it may take its own sweet time about setting the code because its doing its misfire detection by crankshaft speed variation routine, and it has to detect that consistently before it will set the code. You might even need to drive around the block after clearing the codes before it will decide that yeah, its a real fault and it had better set the code.

If the code stays with the same cylinder, I'd check compression and the injector.

Reply to
Steve
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Interesting! I still would have suspected that it would set a coil code in that case, because the computers (I'm pretty sure) look at more than just the primary resistance. They look at the current rise time, and that should have been way off. But then, I'm thinking first-gen 3.5, and maybe they deleted the rise time measurement when they added more sophisticated misfire detection by looking at the crank speed vairation.

Bravo! And much better than having try to diagnose a fuel injector problem.

Reply to
Steve

Well - according to Dr. Bllsht, it will never happen anyway because the PCM will be learning the baseline from the present conditions. If the present conditions are with a steady cylinder miss, that will become the new baseline. So it will think the miss is the baseline and will not set a code for any current anomalies.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Reply to
Bill Putney

So the new baseline that it learns will include any anomaly, such as any cylinders that are missing. That being the new baseline, it will think any missing (the new baseline of "variance between cylindrs") is normal operation and will never set a code (until reset again under new conditions)?

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Reply to
Bill Putney

I called a non-Chrysler service garage (Canadian Tire) and asked specifically about fuel injector issues, and whether they test or clean them. Answer was that there's basically only one place in town that tests injectors (and everyone, maybe even the dealers too, send injectors there for testing), and that plugged injectors are VERY rare.

Based on that, I refocused on the coils.

Reply to
MoPar Man

No. The baseline is learned during a hard (fuel shutoff) decel condition, which takes a misfire out of the equation. Sometimes it takes a few of these, and sometimes it needs to be driven a few miles after it's learned before misfire detection is re-enabled. Without a good scan tool that can tell you if misfire detection is enabled, you don't know if the fault didn't set because the misfire's gone or the PCM's not looking.

Reply to
bllsht

That's not what I said. See my other reply.

Reply to
bllsht

They say it will read and clear codes. If it does what they say it'll do, and that's all you want to do, then yes.

Reply to
bllsht

I would think then that you would still need to reset so you can see what does eventually come back as far as codes. Otherwise you don't know if the codes is old (obsolete news or not.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Reply to
Bill Putney

Your lucky. My last failed coil failed by arcing internally, the problem wasn't visible with a DVM.

Ted

Reply to
Ted Mittelstaedt

Reply to
philthy

Which is the point of my original reply in this thread. There is a difference between clearing codes using a scan tool or code reader, and resetting the PCM by disconnecting the battery. Clearing codes won't disable misfire monitoring by resetting the baseline value learned by the PCM. Disconnecting the battery will.

Reply to
bllsht

Got it.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Reply to
Bill Putney

Wouldn't any of the old 'ignition analyzers' that used to be popular show the reduced high voltage?

Then again, those old analyzers are probably getting hard to find.

I had a GLH-Turbo years ago, and had a misfire problem. Two dealers couldn't find it. One wanted to 'shotgun' the problem at my expense. At least he was honest and told me it was a shotgun fix. NEITHER dealer even was close to the problem. The car had about 80K on it so it was way out of warrantee.

One day the car was missing and backfiring so bad I brought it home and went in the house to get stuff to look. Came out, it was fine. The only thing that made sense was the engine warmed up. So I tried to cool it down with cold water on the radiator. Still was fine.

So, I got to thinking. It was foggy and damp that day. So I took the hose and fine misted in front of the air intake around the headlight. The car really started misfiring. Stopping the mist didn't stop the misfire. I almost went into a panic. I took a hair dryer and blew hot dry air at the light. The problem cleared up in seconds.

I thought it was something in the throttle body, so I disconnected the air hose and tried it there. That didn't affect the problem.

Turned out they had placed a circuit board in the air tube right behind the headlight. The board was encased in epoxy with one transistor sticking out and corroded. Guess what? That transistor fired the coil!

I was going to try to fix it, but I picked up a complete board and duct assembly at the junkyard for less than $50.

Reply to
Mike Y

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