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.

 

MoPar Man wrote:

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.

 

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')

 

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')

 

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.

 

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.

 

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

 

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.

 

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')

 

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

Ted

 

go out and buy some good plugs replace them all !do not use bosch plugs
ngk has some good ones at a very affordable price
swapping coils is a good thing like glenn stated but if you don't have a
scan tool that shows misfires then it is a waste of time. in your case it
will still run rough .
accell products now sell super coils at a very affordable cost 30 to 50
dollars new or a salvage yard.throwing cheaper parts at since you don't
have a scantool if you have a 2.7 engine it could be the signs of a timing
chain jumping time but that will usually show a cam senser code too
if you want for good measure go to a dealer and get a couple cans of
combustion chamber cleaner and follow the instrutions to a tee this
chemical is the best I found for cleaning carbon off the valves which can
also set the misfire code if all checks out good after this then a
compression test of the engine is in order

 

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.

 

Got it.

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

 

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.