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Old 08-22-2003, 02:17 PM   #1
Craig W
Scooby Specialist
Member#: 643
Join Date: Dec 1999
Chapter/Region: BAIC
Location: Redwood City, CA, USA
1999 2.5RS
WRX powered

Question Lots of misfire CELs

Hey all,

I've got an '02 WRX engine, only mods are a gutted up-pipe, k&N panel filter and light weight flywheel. I've had it since February.

Starting about two months ago, I've been getting CELs for P0301, P0302 and P0303, misfires on 1st, 2nd and 3rd cylinders.

Almost always happens when the car is still warming up, idling at the first stop light from my home, (about 1/8-1/4 mile). I've also gotten the CEL using engine braking down the parking garage ramp as I'm leaving work.

I'd occasionally get these CELs about once every couple months, but now they're happening more frequently within a week of clearing the codes.

I've heard that misfire CELs are fairly common and nothing to worry about. But I'd heard it usually is only one certain cylinder, #3 I think. Since I'm getting the CEL for 3 of the 4 cylinders, could it be some defective part? Any solutions?

Thanks for any input.

Craig W.
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Old 08-25-2003, 09:51 PM   #2
Craig W
Scooby Specialist
Member#: 643
Join Date: Dec 1999
Chapter/Region: BAIC
Location: Redwood City, CA, USA
1999 2.5RS
WRX powered


Any Hypothoses? Educated guesses? Shots in the dark?

Bad coils? bad sensor? touchy knock sensor? bad fuel injectors?
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Old 08-26-2003, 12:19 AM   #3
Scooby Guru
Member#: 7089
Join Date: May 2001
Chapter/Region: NWIC
Location: Western Wa

Lightweight flywheels and lightened crank pulley can cause false knock indications and play havoc with the crank position sensor and the cam position sensor.

It doesn't happen on all cars.

The ecu compares the crank position sensor signal and the cam position sensor signal to determine whether a misfire for a given cylinder has occurred.

If you're not actually misfiring (and it's doubtful that you are or you'd've mentioned it), then it's likely that your lightened flywheel is causing your CEL.

As a precaution, pull your spark plugs and check their gaps.
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Old 08-26-2003, 07:46 PM   #4
Scooby Guru
Member#: 3781
Join Date: Jan 2001
Location: Napa Valley
2002 Legacy GT Wagon
2009 Forester X Limited


I just got my first CEL this past Sunday

P0303 & P0304: Misfires in cylinders 3&4. Both happened when I started the car after getting a cup of coffee, so the engine was still warm.

The dealer sent the codes to SOA and they advised that I be sure not to rev when starting, let the car cool 30 seconds before turning off and to use high-octane gas.
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Old 08-26-2003, 08:12 PM   #5
Precision Tuning
Former Vendor
Member#: 38696
Join Date: Jun 2003
Chapter/Region: Tri-State
Location: Lakewood, NJ
2002 WRX


Do a compression test if you are concerned about the codes. They can be set by a million things, but have the integrity of the motor verified. Most shops only charge an hour to do it. Low compression in say cyl 3 can cause a misfire code for cyl 3, or for the previous or next cyl in the firing order. It is all based on the speed at which the crank sensor "sees" the piston travel down the cylinder. Can be anything from low compression, to a lean cylinder, to a faulty crank sensor etc, etc....

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