Thread: Ask a tuner...
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Old 03-25-2010, 07:49 PM   #26
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2014 P3 Import Auto
AWD Dyno, Mods, etc


Originally Posted by Marlons101 View Post
why is my cel on for misfire but no codes show? why does it flassh atl low rpms but not at high rpms?

I have changed plugs, fuel filter, checked lines, cleaned MAF, ....what else should i do? car runs normal just this flashing cel? my gas mileage is **** so does that point to my front O2 sensor?
Misfire codes are temp codes but they are stored. Depending on how your reading them your reader may only be looking at active codes. Basically a misfire code will clear itself after time and become a stored code in history.Misfires can be detected due to an actual misfire you cannot feel or falsely for many reasons. Do you have any lightened pulleys, flywheel? Crank angle sensor could be going bad. Coil pack, injector issue, etc. Timing problem. Need a little more info.

Again were getting into diags not tune specific from what I can tell.

The car is more likely to misfire or detect misfire in lower rpms because the load is higher on the motor and the sensitivity of the detection circuit is better. Some code will actually not even try to detect a misfire at higher rpms. Not sure on yours would have to research but its not really important at this stage.

As for the O2 sensor(front one anyway) the car uses this to fine tune closed loop mode. So when your idle or just cruising the ECU will read the from the front wideband and adjust the trims to match 14.7:1 AFR. Usually when they go bad you get a check engine light, or surging while cruising, hunting idle, smells rich, black smoke, etc. It could be possible that yours has skewed somehow to give off readings making your car richen up the mix thinking its hitting 14.7:1. I would say this is very unlikely but a very rich idle would cause misfires. You could figure it out by logging or using learningview.exe. The learned trims will be positive numbers over 6-8%.

I seem to remember you had the misfire issues on your old motor as well. I would suspect a part you swaped.
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