Hey all,

I've been dealing with this issue for the past month to no resolution. I've posted it on a few other forums, gotten some good suggestions, but they all lead to dead ends. Nyet & Phila_Dot have also been extremely helpful, but unfortunately I cannot seem to resolve these issues. I have had an audi tech & mercedes tech look over this car and they have no idea what is wrong either.

Background info: Performed a 6 speed swap, while the whole drivetrain was out I resealed the engine and replaced almost every hose on the car. Flashed a base tune from Daz in December and I've been dealing with wonky fuel trim values since. The car is K24 RS6'd, 3 bar map sensor, 630cc injectors, and all the stage 3 supporting mods.

Symptoms: The fuel trims read around +6% to 7% at idle, and -18% to -20% at partial in measuring blocks 032. I almost always immediately get a P1557 Positive Deviation code, so logging data is almost useless as it throws the car in limp as soon as I drive it.

I know the most common reply to these issues is to do a boost leak test. I've tested and tested this car to no avail.

Troubleshooting:
Here's what I've tried so far to bring you guys up to speed, I only used OEM parts unless otherwise noted:

• -Tried 3 OEM hitachi mafs and 1 non OEM maf, I've tried them all and they all have wacky trims
• -Replaced both green check valves by the intake manifold to rule out any internal leaks, checked the replacement green valves for function before installing, they are in the correct orientation as well
• -Made sure the check valve on the brake booster hose was good
• -Re-checked the re-built spider hose for leaks as well as check valve functionality, there is suction at the pancake valve at idle
• -Removed the brake reservoir vacuum sensor and replaced w/ a straight fitting (this sensor was left from when the car was tiptronic)
• -Threw on my OEM DV's just in case (as a regular pressure test will not reveal a leak here due to equalized pressures on both sides of the DVs)
• -Replaced all o-rings on the spider hose quick connects to rule out any leaks there
• -Checked the vacuum line running from the intake manifold to the FPR (as this would cause exactly the lean idle & rich partial trims)... lines looked great
• -Replaced intake manifold gaskets to rule that out
• -Replaced coolant temp sensor as I thought it may be faulty keeping the car in open loop mode
• -Replaced the n249, as well as the combi valve it is attached to
• -N75 lines were replaced during the rebuild, and checked with a mityvac and the lines hold vac with absolutely no bleed down.
• -bypassed the N75, ran the car on wastegate pressure, holds pressure to 14-15 psi

Things worth noting: Everyone that has looked at my logs, has mentioned that the MAF voltage reaches almost its limit (4.5-4.6V) at only 17-18 psi.

Also here is a log (albeit in limp mode) for anyone interested: https://drive.google.com/open?id=0B6rUs76HSzcUWkFEdzB4QnM4SlE
   
At this point I'm willing to try anything (I will balance a pancake on my head and hop on one foot if it will solve my problems). I really don't want to have to drop this car off at a shop to have them troubleshoot it, but things aren't looking too good on my end.

Thanks for any advice!

Hi TijnCU, thanks for the reply!

The FPR is indeed the original one with the car (only 110kmiles on it though). I figured if the FPR was bad, it would be lean / lean, or rich / rich in the LTFT's. The fact that it is switching between a lean condition and rich condition at idle leads me to think that it isnt? However, replacing it isnt expensive and I will definitely look into it.

The MAF scaling and MFHLM tables have been checked and sized correctly to the diameter of my MAF housing.

I am running a AEM wideband, logs can be seen above. Fuel pressure is something I need to check, but I am unsure how to check under load pressure, checking idle is not a problem. Wouldn't fuel pressure issues cause misfires / idle issues? I am experiencing none of those.

KRKTE values / TVUB values are correct for the ev14 630cc's I am running. A few people have looked at the binary file and have mentioned that the MAF values are correctly scaled. I have verified that MLOF's is indeed zero. No flow straighteners, but there is at least 6 inches of straight piping before the sensor.

AFAIK the definitions are correct for the ECU.

A bit longer log would be super. Also log msdk_w please.
From this one - I don't like that ps_w is way over pvdk_w (indication of the overscaled MAF). Lambda request in the end of the log is 1.047, which is also weird.

I will try to get an updated log as soon as I can.


I put on factory DV's and drove around, the trims shot back up with my current 034 DV's.

You have a wideband o2, so why dont you just test it? I would pull the maf plug off, drive around for a bit and observe standalone o2 and ecu fuel trims. Easy enough to find out... You probably will be in limp mode, so not much boost  
The only correct way to diagnose your fpr is to stick a pressure gauge in the rail. I don't know if it can cause these issues, but when you are troubleshooting you have to eliminate options. Assumption is the mother of all fuckups  

What does this mean? You observe no difference in fuel trims between those dv's, or you do? The way I read it, it seems you write the trims are worse with the 034 dv's. You can test DV's by applying vacuum to the top and it should remain opened. The closed state can be tested in a normal intake pressure test, or by applying pressure to the dv's individually.

It's not important if there is no ltft, you can monitor the afr on your wideband. Just make sure it does not go super lean.. Its only for verification how the ecu responds to the (missing) sensors...
If the hardware is ruled out you can try to flash a new base file with only fueling mods to figure out what the maf does. If you do bring the car away with custom software, the garage has to be able to tune (in case there is a mistake in the flash...) so I would choose a tuner company with a dyno.
This just came to mind:
Have you tried to do a transparent vac line from the manifold to the fpr? They do leak sometimes, i've had it myself. It will push out fuel through the diaphragm.

No wonder. According to fuel trims and to the log you posted (and assuming your WBO calibration is correct), you're flooding the engine with petrol. With AFRs deep into 10s.

I'd just ignore the "lean idle" for now and concentrate on the "too rich under load". FPR shouldn't do that. I still -strongly- suspect that it's MAF related.