Misfire Codes+Poor Gas Mileage - Subaru WRX Forum
 
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post #1 of 4 Old 12-06-2008, 04:08 PM Thread Starter
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Misfire Codes+Poor Gas Mileage

Good Afternoon,

I'm really sorry if this is a repeat but I have searched for the answers but I cannot really find what I'm looking for.

Okay, I have a 2004 WRX with 86k. It was stock when I bought it at 68k. I have installed the following:

New motor: EJ20, Stock 04 WRX motor (now about 1,800 miles on it)
Invidia WRX Racing Cat Back Exhaust Type R
Kartboy WRX STI Exhaust Hangers Standard Length
Cobb Tuning SF Intake System Black WRX STI
STi Subaru Hood Scoop 2004 - 2005
Cobb 5-Speed Shifter Bushings
Cobb Double Adjustable 5-Speed Shifter
Greddy Subaru WRX Counterweight Shift Knob 5-Speed
Carbign Craft Subaru 04-07 WRX / STI Carbon Fiber Exhaust Heat Shield
STI WRX 5MT Transmission GroupN Mount
Power Enterpise WRX/STi Timing Belt
Beatrush WRX/STi Forged Pitching Stopper
STI WRX Stainless Steel Braided Clutch Line
ACT WRX Street Clutch/Prolite Flywheel Combo
Samco WRX STi Radiator Coolant Hose Kit
NGK WRX One Step Colder Spark Plugs

I have the COBB AP but it is not installed. I also removed my TurboXS BOV-RFL and reinstalled the stock BPV.

Now the Problem is about every 15miles(after reset) I get a check engine code reading P0302, P0303, P0304. Not always all of them but always P0302, and when they are together Cylinder 2(P0302) is always first. These are misfire codes on Cylinders 2, 3, and 4. My gas mileage is poor as well. Is this problem cause by the coil packs? Or do I need to tune/reprogram my ECU? I know the flywheel will throw random misfire codes(learned this after installation not too happy about that), but every thread I have read about that it is always once about every month. Mine throws codes every 15miles(when reset every time). I did have a problem with valve timing on the left side of my motor, but that was fixed. After the new engine it ran great, and I was breaking it in easy, then I started hearing a noise and got my first CEL(2&4), this is also when my mileage went out the window. Turned out one of the bolts on my valve cover somehow broke and thus messed up my timing. This was an easy fix and my timing and belts are fine now. Everything runs great again, except for the CEL and gas mileage. Please help. Thanks a lot!

-Adam

Last edited by AKnox; 12-06-2008 at 05:20 PM.
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post #2 of 4 Old 12-06-2008, 04:25 PM
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There are alot of things that would cause a misfire, injectors, plugs, or the coil packs. I had a bunch of misfires and it ended up being the wire harness connector that plugged into the coil pack, one of the clips was broken of and it would vibrate out of the connector.

BTW why do you reset your ecu all the time?

Dom Tuned 2003 WRX Wagon
251.3 WHP
235.8 WTQ

If it's worth doing, it's worth overdoing
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post #3 of 4 Old 12-06-2008, 05:09 PM Thread Starter
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It's not misfiring just throwing the code. I reset it every time I do something. i.e. change the plugs, clean the plugs, check the coil packs to make sure they are tight, check the wiring harness for clean plugs and good connections, and that there is no damage to it. I'm getting really tired of taking my car apart every day to try and find the problem though.
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post #4 of 4 Old 12-07-2008, 12:08 PM
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if it is throwing a misfire code then it is misfiring.

Dom Tuned 2003 WRX Wagon
251.3 WHP
235.8 WTQ

If it's worth doing, it's worth overdoing
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