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Old 02-12-2014, 08:31 PM   #16
Nikzilla
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Join Date: Jun 2013
Location: Los Angeles
Age: 26
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Quote:
Originally Posted by Kingtal0n View Post
See if you can get a better picture uploaded that I can look at. For now, Ill just throw some ideas your way.

You say the injector duty/maf/tps do not move when the problem occurs. Only the oxygen sensors report a problem. You never answered whether you can feel the engine hesitate or if you can notice that the engine runs differently when it happens?

IF the ECU is not changing any values, but the fueling suddenly changes, something in the fuel system may be causing it. Possibilities are, fuel pump, fuel filter, fuel regulator to name a few. Since you are cruising, and the problem corrects with throttle, the fuel pump is unlikely. If vacuum at the regulator was the issue your wideband would show us a rich condition, not lean. I am still not sure if the engine is flipping out of closed loop, you said the fuel trim sits still. Does the fuel trim normally move while driving? I am unfamiliar with that data tool you are using.

If the fuel isnt changing, that is, if the injectors dont change, and the fuel pressure doesnt change, then the engine cannot suddenly go lean with no reason. Unless the ignition timing is suddenly going really wrong, or getting really weak, such as if you retard the timing 20-25*, THEN you would get a nice fat lean reading suddenly on your wideband, and the engine would lose significant power, and require more throttle position (ive asked already now twice if this happens you never answered). If the car continues driving normal-like, with the same throttle position etc... then we look elsewhere. Also check the ground for the coil packs at the back of the head. And look at your plugs, change them if they are very old or dirty.
I stated in the original post that the car stumbles during this.

And yes, usually the fuel trim does move, but when this particular issue happens, it stands still at 100.

I also have a fuel pressure sensor, and I can say that the fuel pressure remains constant and does not drop not spike when this happens. Brand new Walbro 255 installed too, old one crapped out after the sock fell off. Z32 filter. Perhaps the only thing in the fuel system which I'm skeptical about are the injector O-rings. The injectors never have been touched as far as I'm aware of, but could bad O-rings cause this somehow?

I replaced the coil pack wires recently, and I remember screwing in the ground, but I'll check it to make sure it didn't slip off or something.

Now, timing, could it really affect the AFR? I didn't actually check that, I'll go pull out the log, brb.
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