Horrible negative fuel trims

[mbagge01]

I am hoping someone would be able to get me some advice on tracking down a very negative long term fuel trim issue. I have a 2000 A6 2.7t with EPL stage 3 upgrades (RS4 turbos, 52lb EV injectors, 80mm MAF housing with hitachi sensor, cold air intake) and have their stage 3 tune that is adjusted to be stage 3 minus since I am running a TIP still. I have been running normal short term fuel trims (~ -1.7%) but my long term trims become very negative (rich) maxing out to -25% throwing a CEL and putting the car in limp mode. I have had the car smoked tested and well as boost intake leak tester which were fine. I have replaced all of the solenoid valves and checked all the green check valves which are fine. EPL keeps telling me that despite all this, it is not their tune and something is wrong with my car.

The only thing I have not tried yet is my stock airbox. I have tried different cold air intakes as well as different hitachi sensors with no change. Oxygen sensors are new and have also tried different 02 sensors with no change. The only slight difference i have found is if my cold air intake is a smaller diameter to the 85mm MAF housing with a silicone hose tapering up to 85mm, the short term fuel trims get slight worse (-7%) but the long term fuel trims still are horrible high regardless. Since EPL is convinced it is something on my end, where else should I look. Could I have a crankcase leak or is my pancake valve bad causing a fuel rich issue. I would assume if they sent me the wrong fuel injectors, my short term trims should be way off also. Could it be I just need to use my stock airbox, but I would be surprised that a cold air intake could throw off the fuel trims that much to cause codes due to a rich condition. My problem is either too much fuel going in or a air leak after the MAF. I would appreciate any advice that you guys would have.

[AudiTechS4]

are you sure the injectors are 52lb?

[mbagge01]

I have not flow tested them but EPL keeps telling me they are the correct set. If they were off, wouldn't my short term trims also be way off as well, because my short term trims are not more than -2% off which is very normal

[AudiTechS4]

must have passed over that . what are you using for a fpr ?
also they know you have a 80mm maf and not a 85mm maf correct ?

[mbagge01]

No, my maf is 85mm and I am using a stock 4 bar fpr which I have also replaced, just in case, and their tune is written for this

[Audi_Tech]

What are your values in MVB 32?
Field 1 & 3 are your idle and field 2 & 4 multiplicative (driving) for bank one and two respectively.
If field 1 & 3 are within spec (+/- 5%) and field 2 & 4 are wonky during closed loop then there is a sensor that is reading faulty during load which is most likely the MAF (I don't have much tuned experience for what it's worth).

Not sure if you can drive the vehicle with the MAF unplugged with the setup that you have but doing so will cause the ECM to run on a base MAP dis-regarding the possibly faulty MAF and you're fuel trims might be within spec. If not, then your problem could be elsewhere but something that is a major input to the ECM for load/fuel calculation.

Have you monitored your fuel pressure while driving?

[mbagge01]

Audi_Tech, my additive trims are around -1.7% but my multiplicative trims go up to -25% and obviously throw a code. I have tried 3 different MAF sensors so I do not think that it is the MAF. I have just noticed some oil residue all over the crankcase hoses in the back of the engine. Is it possible that I have a leak in one of there hoses and loosing some air under boost, which normally should reciculate back into the Y-pipe and this is causing my rich long term fuel trims. I have not monitored my fuel pressure readings. Do you know under vagcom which block it is?

[Audi_Tech]

You should hear a boost leak and it should have manifested when you pressure checked the intake system but I wouldn't rule it out.
You can power brake the engine (if automatic) with the e-brake engaged under short durations to check for boost leaks while stationary.

The fuel pressure check is done by a mechanical gauge in-line to the supply side of the fuel rail (lock nut secured connection).

Get a couple engine RPM, engine load and MAF sensors reading at idle and then around every 1,000 RPM and I'll see if I can compare to a calculated load/airflow chart.

[julex]

There is no sensor to read fuel pressure so you cannot read it in vag. However, seeing that at idle you don't hav large trims kind of tells me that FPR is probably ok. Missing vacuum/boost signal or FPR not responding to these properly would result in too much fuel at idle and not enough at boost so the trims situation would be reversed. Now, are you running 5bar fpr?

You need to begin with proper boost leak test. The likely culprit is torn TBB (they like to rip at the bottom so you can't even see it) if it is still stock or some hosing loose... -25% is a lot though and actually tells me that it is more than that since +-25% is regulation limit and you're probably getting CEL for that.

Pray it is not a f.up tune.

Trivia: Block 032 normally shows idle additive and low load multiplicative. When you step on the gas pedal while driving and start moving some air, the multiplicative will start changing from low load to high load trims so that you can see what car does as it gets into WOT area (high load trims are applied to high load).

Also, post a picture of maf/CAI area.

[mbagge01]

I am running a 4bar FPR which the EPL tune calls for. I am considering putting in an adjustable fuel pressure regulator and fuel pressure gauge to adjust the fuel pressure down to see if this helps fix the multiplicative fuel trims which will go up to negative 25% and throw a CEL along with the car in limp mode. Despite all this, my additive fuel trims are always around negative 2%, which would lead me to believe that I do not have a vacuum leak. Does using an adjustable FPR this seem like a reasonable option? I have talked to EPL multiple times and they keep saying it is not the tune. The only thing I have not ruled out is if I was sent the right in injectors from EPL. My indy shop that put them in thought they were a bit overkill for my stage 3 setup. I have replaced my TBB with a silicone one.

[julex]

I am running a 4bar FPR which the EPL tune calls for. I am considering putting in an adjustable fuel pressure regulator and fuel pressure gauge to adjust the fuel pressure down to see if this helps fix the multiplicative fuel trims which will go up to negative 25% and throw a CEL along with the car in limp mode. Despite all this, my additive fuel trims are always around negative 2%, which would lead me to believe that I do not have a vacuum leak. Does using an adjustable FPR this seem like a reasonable option? I have talked to EPL multiple times and they keep saying it is not the tune. The only thing I have not ruled out is if I was sent the right in injectors from EPL. My indy shop that put them in thought they were a bit overkill for my stage 3 setup. I have replaced my TBB with a silicone one.

Have you boost leak tested yet?

[mbagge01]

I have done multiple boost leak tests and had the car smoke tested.

[julex]

"Also, post a picture of maf/CAI area. "

What's your intake like? Exactly what EPL wants or something put together by you?

[mbagge01]

So I may be closer to finding out my fuel trim issue. I went ahead an uploaded to original stage 3 tune they had sent me (This tune boosted to 25psi for which they made adjustments to the tune, lowering the boost to around 20 psi because I am running a tiptronic, which was the tune I have been running recently) and after checking the fuel trims, they are all normal and I am not getting any CEL codes. The STFT are around -4% and the LTFT are around +4%. This leads me to believe that there was a problem with the adjusted tune that they sent me. Is it possible that they lowered the boost parameters but did not make adjustments with the fuel program, which has led to me getting the very negative fuel trims.

[julex]

Fueling is driven by MAF readouts and injector size constant. My guess is that they messed up with changing that constant to smaller injector along with its smaller dead time. This works out to essentially even out at very low injector pulse width (flows vs dead time) from my experience but once the injector starts flowing, it will induce massive fuel trims.

They probably sent wrong tunes to wrong people or gave off the shelf tune for smaller injectors or something silly like that, Either way it will "not our fault"

[mbagge01]

It is uploaded through their own program so I am not sure how to get the file. Could I download them off my car through nefmoto?

[julex]

It is uploaded through their own program so I am not sure how to get the file. Could I download them off my car through nefmoto?

It is most likely copy protected, see my PM though.

[mbagge01]

So EPL is working on fixing the problem for me. Right now their original stage 3 tune is great and pulls hard but it boosts up to 25psi and I do not want to grenade the auto tranny. Do you think that ~20psi would be safe max boost for a tiptronic. I also have a GIAC tip chip and upgraded torque converter.

[aysix]

So EPL is working on fixing the problem for me. Right now their original stage 3 tune is great and pulls hard but it boosts up to 25psi and I do not want to grenade the auto tranny. Do you think that ~20psi would be safe max boost for a tiptronic. I also have a GIAC tip chip and upgraded torque converter.

More boost doesn't always mean more power. Chances are you are making less power at 25 psi on a base tune. They will probably tune you to 22 psi and the auto tranny will be fine.

[mbagge01]

I have read that adding a upgraded torque converter and valve body set will be good enough to protect the tip tranny from a full stage 3. Is there any truth in that.

[aysix]

I have read that adding a upgraded torque converter and valve body set will be good enough to protect the tip tranny from a full stage 3. Is there any truth in that.

i know dannyn on here has an upgraded torque converter and has been stage 3 running K04's for a long time now. I really don't think you need to worry.

[julex]

thumbs up on getting new tune.

[christianb5s4]

aysix, your PM box is full.