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I have a problem with my engine:


It runs lean. Logged from Durametric both banks are lambda 1.2, from idle to about 6k rpm. Above that I've logged lambda 1.
Setpoint is 1.0. The weird thing here is the fact, that idle correction (RKAT) is
solid 0 and lower load range correction (FRA) is solid 1. In other words, Motronic
does not want to adjust mixture at all. This started suddenly, while driving, a
week ago. Since then I've
-checked leaks on intake side. None.
-checked leaks on exhaust side. None.
-checked operation of all solenoids and blocked tank vent line. Nothing there.
-checked all sensors with Durametric, outputs are sensible.
-checked injectors by cutting them off via Durametric. Engine tries to stall with
either one of them off.
-checked effect of fuel pressure by doubling it to 6 bar from tune's 3 bar. No
effect whatsoever to mixture or FRA & RKAT.
-disconnected MAF. No effect whatsoever to mixture or FRA & RKAT, although
Motronic should be rely to WBO2's and drive lambda if MAF is off.
-checked wiring looms visually, and partially with tester.
-No CELs present, except from MAF if disconnected.
-SAI pump is deleted, and holes on cylinder heads blocked.
-BTW, I have separate and independent WBO2s on each bank for my datalogger. They
show A/FR 16-18...
-EGT is around 400C on idle. Unfortunately I forgot to check it when FPR (AEM with
gauge) was set to 6 bar.

So, if there's an intake leak, the should be some CELs present and Motronic should
try to correct the mixture towards lambda 1. With a exhaust leak this kind of
lambda (1.2) could be possible (without CELs), but still Motronic should try to
correct the mixture towards lambda 1. But because both bank's manifolds have the
same lambda 1.2 and they're separate except at very end, there should be similar
leak on ech side. OTH, those independent WBO2s count out incorrect readings from
Motronic. Is my Motronic toast? Is there a certain condition (some sensor
unreliable etc) where Motronic does not adjust mixture with lambda sensors, even
with warm engine?
It has had unexplained MAF problems also earlier. Idle was hunting when I drove
the car day before this incident.

Any help appreciated!

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OK, I looked through my old mails, I haven't been here for ages. I had similar issue 9 years ago and cause for that was then incorrect engine grounding wire. There's two grounding wires in the engine wiring loom, both attach to cam covers' upper bolts. One of the was not installed then. Of course there's the engine grounding line, but's thet's another story.

Anyway, I have checked those this time, but I need to double check them while the engine was off the car and everything stripped away last winter and if I may have accidentally left either of of those loose and vibration has made things worse. The symptoms look awfully alike like ones back then.

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  • 4 weeks later...

Most likely Motronic was partially toasted. Soldering of foot of the largest condensator had a circular crack, visible with microscope. It, among few other suspicious spots were resoldered and problem seems to be gone. First trackday will tell it for sure.

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