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cylinder 3 and 4 misfire error codes, but not misfiring!


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9 replies to this topic

#1 jvanorman

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Posted 09 July 2009 - 03:13 PM

New to the forum...I have a 97 Subaru Legacy 2.5GT that has had all plugs, wires and the coil pack replaced in January. Just 2 weeks ago, the CEL came on, with a cylinder 4 misfire; took it in to my normal shop, no problem found. Just a couple days later, CEL on with cylinder 3 and 4 misfire. Again, took to my normal shop, no problem found. Moved to Las Vegas, CEL on during trip. Took it to another shop, same error codes (cylinder 3 and 4 misfire), but no obvious problem. The car runs great, it is definitely not misfiring. Any ideas on what this could be? BTW, my gas mileage is better than it's been in a long time! Clueless! Please help :)

MORE INFO! The codes were consistent of P0304 and P0303. Once I *STOPPED* using my car charger for my phone, the errors stopped being thrown. Any ideas on this one???

Edited by jvanorman, 25 July 2009 - 10:23 AM.
More info...


#2 CNY_Dave

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Posted 09 July 2009 - 05:20 PM

New to the forum...I have a 97 Subaru Legacy 2.5GT that has had all plugs, wires and the coil pack replaced in January. Just 2 weeks ago, the CEL came on, with a cylinder 4 misfire; took it in to my normal shop, no problem found. Just a couple days later, CEL on with cylinder 3 and 4 misfire. Again, took to my normal shop, no problem found. Moved to Las Vegas, CEL on during trip. Took it to another shop, same error codes (cylinder 3 and 4 misfire), but no obvious problem. The car runs great, it is definitely not misfiring. Any ideas on what this could be? BTW, my gas mileage is better than it's been in a long time! Clueless! Please help :)


I think a misfire is detected by the crank position detector (if a cyl misses that revolution takes longer than normal, something like that).

If that's so, maybe it's something to do with the crank position sensor?

If the CPS reads off of the front 'balancer', maybe the balancer is loose?


Just guessing...


Dave

#3 ferret

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Posted 09 July 2009 - 05:29 PM

Cyl 3 & 4 is the same coil of the coil pack. It could be going bad. Also, when dark, try misting water on the coil pack while the motor is running and see if this arc's or gives you the misfire. The coil pack may have a slight crack and in humid weather arc and give the ECU a misfire.

#4 subsince77

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Posted 09 July 2009 - 07:14 PM

I have about a 75 page post on here about my 97's #3 and 4 misfire problem. I have replaced nearly every electrical component in the ignition system, swapped injectors, even put in a new ecu and a new intake with a new wiring harness on it. I have never been able to track it down, and have stopped trying. My cel is on basically all the time. The car runs fine and never ever actually misfires that I can feel. This problem even followed me through an engine swap.

That does not mean yours is not fixable however. Start with the right NGK plugs and subaru wires if you haven't already. Yup, mist water in the engine compartment, you might just find something. I think my giant thread was called mysterious misfire something or other. It could give you lots of information because everyone on here really beat their brains out trying to find it. Search for misfire and you will find it.

Good luck.

#5 nipper

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Posted 09 July 2009 - 09:49 PM

Just lurking.

Subsince have you tried seafoam?


nipper

#6 subsince77

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Posted 09 July 2009 - 10:25 PM

Just lurking.

Subsince have you tried seafoam?


nipper


Personally or in my engine?

Yes. Seafoamed through the intake, in the gas tank, and sprinkled on the hood. None helped the misfire, but my car runs great. Seriously that was one of the first things I did on the original engine.

#7 Log1call

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Posted 09 July 2009 - 10:27 PM

That code is set because some cylinders aren't firing as strongly as others.

The valves, injectors, compression could be suspect, along with plugs, leads, coils, fuel pressure regulator etc.

The freeze frame facility of the ecu might help point to it.

This code is set as a result of steady driving, it won't get set if you have your foot down or if you are accelerating too much. What this means is that you don't feel the miss like you would if the plugs were missing under load...
So the plugs having the wrong gap and just missing at idle or some narrow rev range when there isn't a heavy load on the motor means you may not notice it. Lean mixtures can also cause these sorts of light throttle miss that can be hard to detect.

If you could drive and log data it may help diagnose it.

I'd start by doing a thorough tune-up and a check of the vacuum hoses.

#8 unibrook

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Posted 10 July 2009 - 08:49 AM

When is the last time your front 02 sensor was replaced?
My bet is that is beginning to get tired and causing the CEL. Don't worry for right now, if this is the issue, your misfires will get worse and worse in the coming months, and you WILL notice it in engine performance. Then you can change it yourself in under an hour. Not a very tough job. :banana:

#9 rvac99

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Posted 10 July 2009 - 09:08 AM

I had misfires and my ECM never knew it. Your ECM might be displaying the wrong code. My ’00 OBW was displaying the wrong codes and caused me a month of aggravation. My problem in threads P0341 and P0340. I had short circuits in my wire harness that were caused by bad seals on the back of plugs B21 and B22. To make a long story short I had sensor wires that, when completely disconnected from everything, had slight continuity with the ground. It was all caused by a conductive fluid that penetrated the wire seals on the back of the plugs.
Not an easy fix. I had to use an eyeglass screw driver to carefully remove each wire from the plug. If you do this, do one at a time so they don’t get mixed up. Once you remove the inner plastic insert there is a plastic tab on each pin that you pry up and then pull the pin and wire out of the back.

#10 subsince77

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Posted 10 July 2009 - 07:12 PM

I had misfires and my ECM never knew it. Your ECM might be displaying the wrong code. My ’00 OBW was displaying the wrong codes and caused me a month of aggravation. My problem in threads P0341 and P0340. I had short circuits in my wire harness that were caused by bad seals on the back of plugs B21 and B22. To make a long story short I had sensor wires that, when completely disconnected from everything, had slight continuity with the ground. It was all caused by a conductive fluid that penetrated the wire seals on the back of the plugs.
Not an easy fix. I had to use an eyeglass screw driver to carefully remove each wire from the plug. If you do this, do one at a time so they don’t get mixed up. Once you remove the inner plastic insert there is a plastic tab on each pin that you pry up and then pull the pin and wire out of the back.


Where are those plugs? This may be one thing I have not done.
NEVERMIND, I FOUND THE THREAD.

Edited by subsince77, 10 July 2009 - 08:08 PM.





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