RET

Are there pictures showing the locations of the electrical ground (earth) connections for a 1998 A8 Quattro (at least for the central electric panel)? The written descriptions are too vague to be of much help given the hidden nature of the connections.

icrashcars

here is one of them...see thread. these often get corroded and cause issues.

quattroworld.com Forums: D2 A8/S8 (1997 - 2003)

RET

I would like to clean and renew the ground connections because of some strange problems that intermittently occur. I had thought that this would be a more-or-less common task, but searching the forum has not helped to find the locations of the ground points....

Anyone?

icrashcars

Did you not read the thread I posted? Simply checking all your ground connections will yield far less results than properly testing your electrical system at the proper points.

Also, the image shows one of the major electrical junctions of the car, which is a known failure point.

RET

Hello icrashcars -

Thanks for the post. I followed the link and read it, but do not think that this is causing the problem that I am having. OTOH, I will clean the connection.

The problem is that the car intermittently stalls at idle or low RPM. This started after a major water leak into the passenger footwell occurred (LHD car - the cover of the the ECU plenum in the engine compartment was improperly installed and rain flooded the area around the relay enclosure inside the cabin).

I might be grasping at straws here: the car had been to two independent shops as well as the Audi dealer and nothing wrong was found, but the problem still exists...

Anyway, I really want to clean the ground connections, and I suspect that they as hard to find on an Audi A8 Quattro as they are on a Porsche 928 (which can have very strange difficulties with improper ground references...).

jfrahm

Might be worth replacing the crank sensor for a problem like this. They are like $15 aftermarket (quality unknown) or $40 Bosch in the USA. Bosch 0261210143. That's a PFL 4.2 part number.

It could also be a bad ECU and as these rarely fail they are probably cheap from a part-out. The main battery connection as pictured would be my first stop though, it probably needs attention even if it's not your problem.

-Joel.

RET

Joel -

Thanks for the reply. I did not want to start changing parts until I could be fairly certain that the cause of the problem had been found. OTOH, the OBD capability is obviously inadequate and can not be depended on, so replacing parts might be a reasonable course...

FWIW, the on board diagnostics do not report any errors. I would assume that the OBD would report a failing CPS. Is this not the case, or can the CPS fail without the OBD noticing? I would not be surprised....

I will add the replacement of the CPS to the to-do list.

Thanks again!

jfrahm

I agree it's not good to throw parts at it. But then it's expensive to pay for diags and not hit the problem.

Does it drop stone dead or sputter and die?
Does the tach drop dead or fade out with the engine?
Does it restart right away or need to be cranked?

You can probably test for CPS or at least spark, monitoring a coil to see if they are sparking when the car is dying.

The fuel pump could be suspected although that seems a bit thin.

The ignition switch is also a possibility.

There is a fuel pump relay down there isn't there? 4D0951253? No idea if there is an ECU relay. Probably super cheap to swap in used or aftermarket replacements.

-Joel.

RET

Hello Joel,

Sorry for the late reply... dealing with this problem has not been high on my priority list...

However, the problem is resolved: it was a bad mass air flow sensor.

I had changed relays and cleaned the recommended connections (none of which were corroded...); all with no change to the stalling problem.

The car had been taken to four service shops, including the Audi dealer: the first place could not even read the diagnostic codes; the second could read the OBD codes, but the errors were minor and not engine related, so the shop declined to work further on the car since the problem had not been identified by the OBD errors; a third shop could read the codes also and thought that maybe the ECM might be at fault since no hard error was shown, but had no way of confirming this; finally the dealership tested the car, found no significant fault codes, and gave the opinion that the fuel pump was responsible and needed replacement.

The diagnosis of a faulty fuel pump was determined by measuring the current, per the WSM, drawn by the fuel pump and was reported to be 3 amps (not the nominal 8...). I pointed out that the car accelerated well and had good power climbing hills at speed, and asked that the dealer guarantee the results (i,e,, if the new pump at $1800.00 did not cure the stall, I would not be charged for it...) they declined, of course. FWIW, later that day I measured the current to the fuel pump at 7.9 amps...

The momentary losses of power at low RPM were similar to the symptoms of the failing MAF sensor on my '89 928 GT Porsche, so I unplugged the MAF on the Audi and the stalling problem went away (note that the gear selector indicator on the instrument panel displayed in error mode). The car even drove well.

A new Bosch MAF sensor cleared the error and seems to have solved the stalling problem.

Bob