P1136 & P1138 System Too Lean (Add) - Block 107 System Not OK

[rn3037]

Seeing if any gurus here can help, I have a 2004 A8L with the 4.2 V8

I can't get rid of P1136 & P1138 - Here is a list of stuff I replaced/checked. The thing I notice in my logs is that usually on a cold start, the car will add 10-14% fuel in both banks but once it warms up fully it only adds 3-4% and it's also negative at times.

BLOCK 107 BASIC SETTING (System Not Ok)
Any idea what causes this to fail? Whenever I test, it always goes to 25% fuel and fails. The strange thing is that I unplugged the MAF and it passed.

-New O2's
-New Coolant Temp Sensor
-New MAF & swapped known good MAF
-New Fuel Filter
-New PCV Valve
-Checked for vacuum leaks
-Swapped good Evap Valve
-Plugged off Secondary Air Injection vacuum lines to eliminate the possibility of leaking SAI pump



UNPLUGGED MAF




17544/P1136/004406 - Fuel Trim: Bank 1 (Add): System too Lean
Possible Solutions

Check Mass Air Flow (MAF) Sensor
Check Fuel Pressure Regulator
Check Fuel Pump
Check Intake/Exhaust System for Leaks
Check Secondary Air Injection for Leaks
Check Vacuum Lines for Leaks

Special Notes

Fuel Trim Info
When this fault is stored and external vacuum leaks are not found, less obvious problems may be present:
Check Evaporative Emission (EVAP) Canister Purge Regulator Valve (N80)
Check Brake Booster and Hoses
Check Electric Vacuum Pump ( If Applicable )
Check Crankcase Ventilation System for faulty components. When the PCV or Crankcase Ventilation System is faulty, vacuum is typically present under the oil cap and misfire faults are common.

[TheSchwa]

Wrong sub...?

[rn3037]

Sorry I posted here because the A8 groups have very little traffic, I figured I would get more visibility here.

[JimmyBones]

Those codes are about 99% of the time caused by a vacuum leak.

Do you have any carb and choke cleaner or starter fluid? I would try spraying either of those around the intake manifold and vacuum lines with the engine at idle to see if you can get the RPMs to raise. The older timing belt V8s had a bunch of issues with the variable runner flaps on the front of the engine. There are some cool rebuild kits.

[B00sted20VUSP]

I had a vw phaeton in my shop with the same engine awhile back that had a bad fuel pump causing lean faults (same engine)

[rn3037]

Jimmy Bones - I tried spraying fluid, no change in RPM. I also get about 17-18 inches of vacuum at idle so it looks ok. ALSO, the air fuel is basically never lean from what I read in block 031. For some reason the car adds 10-14% of fuel while warming up then once it's warm, the fuel corrections are normal. I would imagine that my issue is a fuel problem due to the basic setting 107 failing.

Boosted20VUSP-The pump(s) was the next thing that I was thinking, did you test the flow and output?

Take a look at the following logs, the first is of my car that has the codes, as soon as the O2's come on, it starts adding a lot of fuel. The other car I compared it to has no issue and it starts subtracting a lot of fuel when the O2's come on. Any ideas where the issue may lie after seeing this? Also, as mentioned previously, once the car is up to temp around 85-95 celcius, the fuel corrections are very low and negative (normal) it's only like this upon starting the car.

2004 A8L with P1136 & P1138



2006 A8L With no issues

[vacsimile]

Check your air filter. Seriously I know it sounds dumb but when that air filter isn't fitted just right (namely on A8's) it does the same thing. Sometimes the airboxes on these MAF engines get just a little distorted and it changes the way the air flows inside the intake tube. It will end up creating turbulence or a type of jet-stream through the intake tube and it tricks the MAF into thinking that less air is entering the engine than what actually is. Make sure the airbox is assembled snugly and correctly and try wiggling it back and forth while watching your fuel trim values.

[rn3037]

Check your air filter. Seriously I know it sounds dumb but when that air filter isn't fitted just right (namely on A8's) it does the same thing. Sometimes the airboxes on these MAF engines get just a little distorted and it changes the way the air flows inside the intake tube. It will end up creating turbulence or a type of jet-stream through the intake tube and it tricks the MAF into thinking that less air is entering the engine than what actually is. Make sure the airbox is assembled snugly and correctly and try wiggling it back and forth while watching your fuel trim values.

Ok that's a great point, I'll fiddle with it and see if it changes anything. See the tough part is that once the car is up to temp, the fuel trims are not adding very much fuel anymore, the trims looks normal once the car is warm.

Take a look here, just scroll down you can see the fuel trims lowering as the car temp increases.
https://docs.google.com/spreadsheet/...=sharing#gid=0

[vacsimile]

Ok that's a great point, I'll fiddle with it and see if it changes anything. See the tough part is that once the car is up to temp, the fuel trims are not adding very much fuel anymore, the trims looks normal once the car is warm.

Take a look here, just scroll down you can see the fuel trims lowering as the car temp increases.
https://docs.google.com/spreadsheet/...=sharing#gid=0

That's a pretty slick spreadsheet you got yourself there. Is the timestamp field in seconds? It seems like it's running lean consistently until that 254 second mark, then it drops down to normal. The secondary fuel pump (left side of tank) only runs at cold starts and above so many RPM's, I can't remember how many exactly. I wonder if this has something to do with it... Like it's expecting to have the extra fuel at first but isn't getting it. Not sure about that one, kinda grasping at straws. How is engine performance at high RPM's? I'll check up on the details of the secondary pump and post them later.

[rn3037]

That's a pretty slick spreadsheet you got yourself there. Is the timestamp field in seconds? It seems like it's running lean consistently until that 254 second mark, then it drops down to normal. The secondary fuel pump (left side of tank) only runs at cold starts and above so many RPM's, I can't remember how many exactly. I wonder if this has something to do with it... Like it's expecting to have the extra fuel at first but isn't getting it. Not sure about that one, kinda grasping at straws. How is engine performance at high RPM's? I'll check up on the details of the secondary pump and post them later.

Thank you very much for the reply man! Yea I think the timestamp is in seconds and the car drives totally normal at WOT and cruising speeds. The air fuel seemed spot on too at WOT and cruising with only maybe 2-4% correction. That secondary fuel pump hypothesis could be it. The "Fuel Supply System" is what's failing the basic settings and the supply system is basically just the fuel pumps.

It's a long shot but I was wondering if the actual ECU is the culprit. Whenever I reset the check engine light vai Vag Comm, the car adds 25-27% fuel instantly every time. Then after it warms up it goes down to somewhat normal corrections. I'm also wondering why the fuel trims are perfect with the MAF disconnected.

[vacsimile]

Thank you very much for the reply man! Yea I think the timestamp is in seconds and the car drives totally normal at WOT and cruising speeds. The air fuel seemed spot on too at WOT and cruising with only maybe 2-4% correction. That secondary fuel pump hypothesis could be it. The "Fuel Supply System" is what's failing the basic settings and the supply system is basically just the fuel pumps.

It's a long shot but I was wondering if the actual ECU is the culprit. Whenever I reset the check engine light vai Vag Comm, the car adds 25-27% fuel instantly every time. Then after it warms up it goes down to somewhat normal corrections. I'm also wondering why the fuel trims are perfect with the MAF disconnected.

When you clear DTC's you're also clearing long term fuel trim data, and short-term is relative to long-term. So once long-term sets at, say 25% and short term reads at 3%, that's actually 28%. So by clearing fault codes you're just getting an unbiased reading from your short term.

I couldn't find any of the info I mentioned earlier, sorry. But after looking back at your original post I'm convinced the problem is air related. If there was a fuel delivery issue the results of 107 would fail, with or without the MAF plugged in. You're not getting any less air into the engine with it unplugged and the ECM just assumes that it's getting its normal X.X g/s of air at idle. The results change which means the MAF is lying. Your MAF is a liar. Considering you've replaced it, this can only mean that you have unmetered air. You have a vacuum leak or air is streaming around the hot-wire sensor. Test by removing the airbox altogether leaving just the MAF on the end of the tube, clearing your DTC's and running 107 again. If it passes, the problem is before the MAF. If it fails it's a problem after.

[RPMtech147]

You need to take it to a shop that knows how to find a tiny vacuum leak. If they don't have a good smoke machine, they don't know really know how to diagnose a lean code.

[rn3037]

When you clear DTC's you're also clearing long term fuel trim data, and short-term is relative to long-term. So once long-term sets at, say 25% and short term reads at 3%, that's actually 28%. So by clearing fault codes you're just getting an unbiased reading from your short term.

I couldn't find any of the info I mentioned earlier, sorry. But after looking back at your original post I'm convinced the problem is air related. If there was a fuel delivery issue the results of 107 would fail, with or without the MAF plugged in. You're not getting any less air into the engine with it unplugged and the ECM just assumes that it's getting its normal X.X g/s of air at idle. The results change which means the MAF is lying. Your MAF is a liar. Considering you've replaced it, this can only mean that you have unmetered air. You have a vacuum leak or air is streaming around the hot-wire sensor. Test by removing the airbox altogether leaving just the MAF on the end of the tube, clearing your DTC's and running 107 again. If it passes, the problem is before the MAF. If it fails it's a problem after.

I ran with no airbox and had the same results, I did notice that of course when I put my hand over the front of the MAF, the car instantly adds max fuel to prevent stalling out. I'm wondering if when I run the BLOCK 107 settings and when the car initially starts up, if the Throttle Body is somehow closed more than usual, not letting enough air in.

Whenever I press "ON" for block 107 Basic Settings, I can hear the intake suck air and the engine bucks a little bit almost like when I put my hand over the front of the MAF. The 2006 car does NOT do this, the RPMS stay perfectly steady when I run the test.

You need to take it to a shop that knows how to find a tiny vacuum leak. If they don't have a good smoke machine, they don't know really know how to diagnose a lean code.

This was my initial thought until I watched the behavior, if it had a vacuum leak the fuel trim would always be adding a large positive amount. I tested this by disconnecting a vacuum line in the intake as well as the plastic tube after the maf on the intake pipe, both times of course fuel maxed to 25% but before I removed these the trims were perfectly normal. Once the car gets warmed up it behaves exactly like the 2006 A8 that I am comparing it to. It's very strange, it really looks like an electrical issue now.

[rn3037]

*FIXED*
Used smoke machine at my local mechanic shop, big leak on the valve cover gasket. The stupid thing about this is that I actually did the valve cover gasket when I bought the car so when I re-installed the gasket I must've 'creased' part of the gasket so it didn't seal. Lesson is ALWAYS look at the simple stuff first and if you 'touched' anything on the car.

[RPMtech147]

awesome...this is the machine I have...

I spent a stupid amount of money on it but it's well worth it. The first time you use one successfully you'll wonder how you ever did it without one.