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Old 04-04-2013, 09:19 AM   #3
Cobb Tuning
Member#: 4803
Join Date: Mar 2001
Location: Austin, TX

Originally Posted by ortag49 View Post
Hey Everyone, I have 2009 WRX running an AEM CAI with Accessport Stage 1+ tune. I was on holidays and fueled up at gas station in a small town, I was a little apprehensive about the 91 octane seeing as it probably doesnt get much use, but I needed gas. I got back onto the highway, sped up to merge and the CEL comes on. Thought ****!! Bad gas, gas cap not tightened? Checked the code on my AP and it read PO304 PO303 PO302 and PFFFE. I tightened the gas cap reset the ecu and drove home, roughly 500 miles, no issues. That was 4 days ago. Tonight, get into my car, start it and bang, CEL comes on. Same codes. Can someone please help me out here. Is it Spark Plugs? Coil Packs? MAF? The fuel from the gas station is out of the tank so it cant be that. I could see there being one code from a bad coil pack but 3? Is that possible? Any help is appreciated.
Pull up your A/F Learning 1 A,B,C,D monitors via the live data function on the Accessport (connected to car with ignition ON) and report back each value. Each individual value should be within around +/- 5%. If any one or more is way outside of that, a mechanical fueling issue could be ruled in as possibly a contributing factor. Make sure you've driven at least through a full tank of gas before relying on these values - that might be a good idea anyway as you might have had some bad gas and although you filled up again, depending on how empty the tank was when you filled up, it might still be a problem.

After you reset the ECU, were the codes that came back exactly the same as previously listed? Can you list all the mods that you have? Some, like a lightweight flywheel or crank pulley can cause false misfire reporting.

Problems with coil packs or injectors can certainly cause misfires, but it would be unusual for you to get multiple cylinder misfires for that to be the case (usually a single cylinder problem - not 3 at once). That would generally point to issues that effect all cylinders rather than individual cylinders.

If you have any neglected maintenance (or bought the car used and don't know when it was last done) - spark plugs, fuel filter, etc., I would take care of that now. It would need to be done anyway so best to do it now and rule it out as a cause.

I wouldn't do any aggressive driving until you figure out the problem.

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