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Open/Closed loop and ECU questions
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Posted by JamieP (more from JamieP) on Tue, 7 Apr 2015 16:00:21 Share Post by Email
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I've been fighting a lean running condition with my 88 turbo, it has a few modifications such as RRFPR, 30lb injectors, SD red series turbo, AID, 2.1 head & manifold. Under most conditions the AFRs are running at 14.7 to 15.3, even under WOT and full boost, it starts detonating at about 9 psi and the APC cuts it back. At first I figured this was a vacuum leak but I cannot find anything, I've replaced hoses, manifold grommets, made sure the intake system is sealed so Im thinking its something with the fuel injection system. I've back pinned inputs and outputs on the ECM and everything seems to be within specs according to some sources on here and the Bentley manual. I've also swapped ECUs and AMMs, the ECU did not change anything, I swapped AMMs and one was a little better, Its the one giving me the AFRs listed above.

My question is, does the ECU go into open loop only at wide open throttle or are there other conditions that it will? If everything is working properly shouldn't my AFRs show richer under WOT, currently its right around 14.7 at WOT. I've checked the throttle position switch signal at the ECU and at WOT it reads 5 volts.

I'm hoping somebody can shed some light on this situation, I've been fighting this problem for about a year now. Thanks for your help.


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