Hi,

I have a 1999 A6 Quattro. I'd rather fix the car myself however my knowledge to diagnose is still limited. I am hoping someone can help me to interprete the codes here to find the real issue:

6 Faults Found:
17544 - Long Term Fuel Trim Add.Fuel,Bank1 System too Lean
P1136 - 35-00 - -
17546 - Long Term Fuel Trim Add.Fuel,Bank2 System too Lean
P1138 - 35-10 -
16839 - EVAP Emission Contr.Sys.(Gross Leak) Leak Detected
P0455 - 35-00 -
16825 - EVAP Emission Contr.Sys.Incorrect Purge Flow
P0441 - 35-00 -
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-10 -
16690 - Cyl.6 Misfire Detected
P0306 - 35-10 -

Can someone let me know where should I start?

Thanks in advance.

 

I would imagine the engine is running rough yes? Don't worry about the EVAP fault codes for the time being, as they don't affect engine performance.
Start your diagnosis by looking for vacuum leaks, giving that its lean on both banks its gonna be a large leak probably close to the MAF sensor (after it) before it enters the intake manifold. If you can't find anything there, disconnect the MAF sensor and see if the engine runs better. If it runs smoother with the MAF disconnected the ECM has already adapated to not using it and the MAF is the problem.

 

Thanks Auditech79.

Just one quick question, some other threads were mentioning Purge Valve related issues; would it be possible that I have the same issue here?

Thanks.

 

The "purge" valve you are referring to is the N80 valve for the EVAP system. The evap system reciculates gas vapors from the gas tank back into the intake to be burned, preventing the vapor from reaching the atmosphere. This system has no affect on engine performance unless there was a massive leak from one of the combination valves.
That still wouldn't cause a lean fault code on both banks most likely. The N80 valve is sitting on top of your airbox if you want to check it out for cracks or leaks.

 

While I have never had this code, I would be interested in the "Gross Leak" issue. If you evap system has a leak and is sucking air into the intake, it WILL make you run lean. I would disconnect the evap control solenoid and see how your codes change.

The misfire codes may or may not be related. Fix the lean issue then look into the misfire.

OBTW, you might want to tell us what engine you have.... I assume 2.8.

 

Mike,

Yes it is a 2.8 AHA.

Yesterady before I start doing what you and Auditech97 have suggested, I checked on the codes again and this time it only says "gross leak" and one of the banks is running lean. So I cleared the codes again to see if I get anything different today.

But just to clarify, even with all these codes, the engine has been running as it was before when there was no code.

Thanks.

 

Well you never really told us how it runs. Can you feel the misfire? Is there a lack of power? Can you hear a sucking noise under the hood with the engine running?

 

OH BTW, don't clear the codes over and over. Everytime you do that you re-set the ECM's memory clearing the fuel data blocks which is something i would need down the road to diagnose it. In fact i was gonna ask you to check data block 32 but you will have to drive it for over an hour now to get the fuel trims back.

 

Thanks Auditech79. I have not been able to work on it yet. But I did observe one thing. Now every time after I fill the gas, which obviously involves openning the cap and close the cap, I will have hard time to start the engine. I will need to floor the gas, then start the engine; and for the first a few seconds, the engine will be running pretty rough, I will have to put my foot on the gas to help it to maintain the RPM or it will die; but after that, everything seems to go back to normal, no problem starting the engine either.

would this be a related problem?

 

If you are dealing with a large enough vacuum leak it could be that yes. However, if you have a leak that large it should be easy to find.