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Old 08-03-2010, 04:03 PM   #53
Scooby Newbie
Member#: 159325
Join Date: Sep 2007

First, thanx a lot for your input.

1.- I didnt check that thoroughly but the FPR has been changed for a new one lately.

2.- I will check that.

3.- I had the front 02 sensor changed under warranty at the dealer with no effect whatsoever. I had the rear 02 sensor changed as well with no effect.

I know from the tool I have made to display SSM data that the AF Correction is swinging when I let the gaz or jump on it. It is also swinging when the hesitation occurs at CONSTANT light pedal input...

and rear 02 sensor can cause the ecu to trim fuel up to 25% I think from what I have read. I need to go further in my disassembly effort to confirm.



Originally Posted by P3Auto View Post
I'm not sure if you have done

this but I would check the following:

1. Check fuel pressure at idle and make sure that it rises 1psi for ever 1psi of boost. Drive around with the gauge and look to see if you have any strange pressure drops or changes while cruising and in your rough spot.

2. Use rom raider to log the roughness monitors on #1,#2,#3,#4. Look at the roughness while at idle in real time then give it a little throttle, make note of a cyl showing more roughness then the others. Try cruising and watching this. If you can isolate it to a cyl you may consider swaping that injector then the coil pack. I have run into issues with faulty or leaking injectors as well as coil packs causing your problem.

3. Swap the front O2 sensor again with a known good one. You mentioned when you disconnected the rear sensor your problems stopped. Thats fairly odd. Try disconnecting the front sensor and see what happens. The car usually uses the front sensor to trim the fuel, it responds very fast with short term fuel trims, when the front sensors start to go bad a classic symptom is what you described. You may be able to spot a sudden trim if you log rpm and af correction #1 if there is a sudden swing in fueling this should show it. Try to log as little as possible to keep the definition high in the logs.
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Last edited by Daluv; 08-03-2010 at 04:54 PM.
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