Re:Re:RE: P0300

Hey Team, kind of stumped on a P0300 code set on a 2007 Jeep Compass, 2.4 Liter. tests preformed already include---> coil swap, plug swap, injector test and swap, compression test all cyl at or around 145psi on all, fuel trim is srt trm 0 , Long term at 2.3, ect test good. fuel pressure is good. mass air at 4.5 to 4.8v at idle, tested for vacuum leaks and found none. can provide more info if needed tomorrow. { story is } no misfire recorded at idle. only recorded when giving fuel in park or drive. engine runs smooth during episode misfire counter climbs on scanner but as I said engine runs smooth, and has no engine noise . motologic shows no pcm update. engine has 82k miles. Any Ideas? Thanks

Does your missfire counter show which cylinder is misfiring?

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yes I'm sorry 1 and 4

cyl 1 and 4 shows the misfire count

But you can't feel a misfire at all when the counter is saying there are misfires?

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nope not at all lol even test drove and all was smooth

I'm thinking maybe valve springs week

I hate spell check lol

Well I think a leak down test is in order. A running in cylinder capture would be great but that is a set of tools you probably don't have access to? There's a low tech way to do this with a standard compression tester with the engine running, But it's pretty rough on the hoses to say the least so I wouldn't do it to my set....

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Your mass air seems a little high for idle on a warm engine .what do STFT do if you power brake it where it counts misfires?

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power brake, fuel trim goes rich

I have a leak down test gage. I will perform test in the am.

stft moves a little but returns to 0 quickly.

Actually, I've seen this before. :lol: On the same engine. I was able to watch the misfire counts tell me there were dead misfires when I could feel the engine run perfectly.

I was never able to determine what the initial problem was, but I know I got the false misfires to quit with a soft reset. Disconnect the battery cables, short them together with a test light, leave them for half and hour and come back to it. I bet the code and misfire counts will be gone

Aren't 1 & 4 companion cylinders on these engines ? If so for me that points back again towards ignition. With wasted spark an open plug lead can take down 2 cylinders.

Tyler wrote: Actually, I've seen this before. :lol: On the same engine. I was able to watch the misfire counts tell me there were dead misfires when I could feel the engine run perfectly.

I was never able to determine what the initial problem was, but I know I got the false misfires to quit with a soft reset. Disconnect the battery cables, short them together with a test light, leave them for half and hour and come back to it. I bet the code and misfire counts will be gone

I like it

Tyler wrote: Actually, I've seen this before. :lol: On the same engine. I was able to watch the misfire counts tell me there were dead misfires when I could feel the engine run perfectly.

I was never able to determine what the initial problem was, but I know I got the false misfires to quit with a soft reset. Disconnect the battery cables, short them together with a test light, leave them for half and hour and come back to it. I bet the code and misfire counts will be gone

Now we're getting somewhere! I was thinking that this has to be a software problem if he can't feel any misses but it's logging like crazy . Wonder why there's no software update for this ECM it sounds like it has affected more than 1 of these vehicles

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Ben wrote:

Tyler wrote: Actually, I've seen this before. :lol: On the same engine. I was able to watch the misfire counts tell me there were dead misfires when I could feel the engine run perfectly.

I was never able to determine what the initial problem was, but I know I got the false misfires to quit with a soft reset. Disconnect the battery cables, short them together with a test light, leave them for half and hour and come back to it. I bet the code and misfire counts will be gone

Now we're getting somewhere! I was thinking that this has to be a software problem if he can't feel any misses but it's logging like crazy . Wonder why there's no software update for this ECM it sounds like it has affected more than 1 of these vehicles

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I wondered the same thing! I searched and searched for some kind of history on this problem, never could find one. I ended up letting mine go after the soft reset.

I wondered about a shifted flex plate, but the cam/crank waveforms were perfect. Best theory I have is the misfire detection monitor getting confused somehow, and ends up tricking itself.

I've heard of sloppy drive belts or tensioners flagging these codes, but haven't run into it myself as of yet.

I am dealing with this right now on a 2.4 L with cylinders 1 and 4 showing misfires but there are no misfires! Was looking in my own forum for some help and it seems I may have found some
Any other updates from you guys on this?? Thank you!