rn3037

Hmm, I'll spray some soapy water on the injector o-rings to see if air could be leaking from there, that's a good one.

I just swapped the EVAP purge valve from another car because that is listed as another possible culprit for these lean codes. We'll see.

rn3037

NEW O2 Sensors
NEW Intake Manifold Gaskets
NEW Injector O-Rings

I installed the above items but I still have the fuel corrections at idle on a cold start. The fuel corrections go from 10-12% down to 0 or negative once the car reaches 60-90+ degrees. You can see the change start happening in my log file around ROW 545.

Any ideas on what could be causing the addition of 10-12% fuel only at idle until the car warms up? The car is also very lean on a cold start sometimes, Block 031 shows Lambda at ~1.3-1.4 during the high idle cold start, then it settles down to 1.0 when the RPMS drop. I have no secondary air injection codes but I think it's broken, I can't hear or feel it working, not sure if that could be causing this.

LOG FILE
https://docs.google.com/spreadsheet/...mc&usp=sharing

dvs_dave

How tight are your inlet manifold bolts? Mine were pretty loose (hand driver tight) for some unknown reason and the engine made a squealing sound at idle when hot from the air leak. It didn't throw any codes but tightening the bolts down (12 lb-ft) fixed the issue.

You could have the same issue, just it's not making a noise as it's leaking more air through a bigger gap?

rn3037

I re-tightened the intake manifold bolts when putting it back on so it 'should' be fine, I hope

The problem seems to be electrical or ECU driven because the computer stops adding 10-12% ONLY after the car reaches a certain temperature. I'll do some more logs driving around too, but I also don't really see the Air Fuel go lean so it looks like the lean codes are being tripped by these fuel corrections.

Possible Temp Sensor at fault?
These cars don't have an Idle Air Control Valve right? That would be my next guess.

rn3037

I just checked block 031 on my 2006 A8L and it does the same thing where it goes 1.2-1.3 Lambda on a cold start, then it goes down to 1.0

The only difference is that this car adds over 10% fuel at times and it's basically only when the car isn't warmed up. I eliminated the possibility of vacuum leaks, MAF, Fuel, etc...

Anyone think the ECU could have an issue? It fails Block 107 basic settings too and that is the fuel control module. I don't know how I'm getting these lean codes when I don't see the Lambda go lean once the car is warmed up driving normally.

jakematic

Was this an OEM MAF - from a dealer?

Reason I ask:


See also: http://forums.ross-tech.com/showthre...05-Phaeton-W12

rn3037

It was a Bosch sensor and housing, it's definitely not the MAF because I tried this brand new one AND the MAF from my 2006 A8L that has no issues at all.

Along with the car adding 10%+ fuel during the cold start, it also always fails Block 107 Basic Settings and then throws the following two codes. The commonality is that all of these issues have to do with Fuel Control. The addition of the fuel above 10% is tripping the lean codes. The car may never have actually gone lean when it's warmed up.

17519 - Oxygen (Lambda) Sensor Regulation: Bank 1
P1111 - 001 - System too Lean
17555 - Oxygen (Lambda) Regulation Bank 2
P1147 - 001 - System too Lean

jakematic

Ah, good to hear it's genuine - just thinking out loud - have heard of many weird things otherwise.

May want to ask Ross-Tech directly for additional guidance as I'm out of ideas

dvs_dave

The ECU only goes into closed loop control once the engine is up to temp. i.e it ignores the lambda sensors until then. In your case once it warms up and switches over to closed loop, it then corrects itself. So you have an issue with the open loop control.
Try unplugging the maf and see what the oxygen sensor values then read. The ECU should default to a base safe map. If the values are still showing too lean then you have a vacuum leak somewhere.

rn3037

I'll try unplugging the MAF and I'll do a log to see what the corrections are.

The only time I see the Lambda go lean is usually on initial cold start before the O2's come on, this is the same even for the car that has no issues. Lambda is 1.2-1.3 BUT the only difference is that the car with no issues starts with negative to 2-3% fuel corrections whereas the car with the codes is at 10-13% fuel additions.

The other thing is that once my car is warmed up, the corrections go to negative or very low % as normal and I never see the Lambda go lean. So in summary, both cars basically act IDENTICAL when warmed up (90+ Celcius) never lean and never large fuel corrections.

VACUUM LEAK - If it was a vacuum leak, wouldn't the car be lean AND adding large fuel % ALL the time?

2004 A8L with P1136 & P1138



2006 A8L With no issues