GregD2ABZ

Dear fellow members,


a big repair has been made on my A8 D2 4.2 V8 ABZ (1996) car's engine, in the past couple of months. It took quite long, because I hade to get some of the necessary parts from all over Europe.

There were oil leaks from the engine, first only timing belt and gasket replacement took place, after that the service noticed, that oil is leaking from the cylinder heads also, so the cylinder heads were also repaired (it has been flattened), and the cylinder head gaskets have also been changed. After everything has been assembled, the first symptom was, that after 1 or 2 seconds after a successful start the engine stalled. They checked ignition and fuel pressure, and after I've read in my country's (Hungary) Audi A8 forum, that fuel pump goes wrong in these cars, we have changed the fuel pump to a new one also, and fuel pressure is good since then, and the engine runs smoothly, it doesn't stall.

But, the next problem is, that the engine won't rotate above 4500 or 4600 RPM, the car takes away the ignition above 4500, and doesn't let itself go above 4500. This happens in kickdown mode, the transmission switches back as it should, but since it can not go above 4500, the trans can not shift up to the next gear in kick down mode, In normal mode the trans works totally fine, shifts up and down as it should. The service thinks that this is caused by the failure of the crankshaft RPM sensor. We could not obtain a new sensor yet, it is very hard to get new parts to D2s here. I've found one in Germany, perhaps it will match.

I've discussed this problem (it doesn't go above 4500) with a guy, who is a big fan of A8 D2s, and owns 5 pieces of them, and has repaired a lot, and he thinks that this is not caused by the failure of the crankshaft RPM sensor. He thinks that because these V8 engines are very sensitive to this, the cylinder heads of these engines are not suggested to be repaired (flattened), because they are not behaving like average engines. If you make the combustion chamber (fire chamber) any smaller then the factory value, then the engine will work abnormally. He said that in the past he got problems from flattening the cylinder heads, but he didn't have tis symptom (won't go above 4500), he had other sypmtoms. He said we should measure the compression in each of the cylinders, the original factory value is 10.8, and we will get values from 14 to 16 bar. The service measured it, and they got these values:

I. 10.5

II. 12

III. 12

V. 11.5

V. 11.8

VI. 11.8

VII. 12.1

VIII. 11

We don't think thet these would be too high values. The cylinder head repair was made by a company who has been dealing with this for more than 25 years by now, and they repair engines not only for cars, but for trucks and buses too, and do their work precisely.


There are 2 error codes, one is something like bad RPM, and the other is misfire in cylinder 5.

Next wednesday the car will be taken to an Audi car dealer's service, and their electrical repairman and the old factory engine diagnostic system will be connected onto it.


Have you experienced anything similar to this? What do you think does really cause this problem? Car won't run above 4500, so I can not make critical overtakings with it, in a normal way it is completely usable and functions smoothly.



Thanks a lot, best regards: Greg from Hungary

jfrahm

If you got a knockoff fuel pump it might not be able to deliver enough fuel for higher RPM operation. I tried one, from Poland (or China via Poland) and it could not develop enough head pressure to push fuel past the fuel pressure regulator. It also did not move enough fuel to run the scavenge system that pulls fuel out of the "feet" of the fuel tank, so I ran out of gas with 1/3 left on the gauge. I suggest checking fuel pressure at idle and if it's low, then that pump is probably bad (or maybe the regulator). If it looks OK at idle then monitor fuel pressure while driving you might see see that it drops off and prevents higher load/RPM operation. If this is difficult then a simpler test is to see if fuel is returning to the tank in the low-pressure line.



You might also see if it runs out of fuel with 1/3 left in the tank, then runs fine if a few liters of fuel is added. In the image the pump assembly is #19, it's up high on the RH side, the pump shoots fuel down to the "feet" to operate scavenge venturi pumps that return fuel to #19

GregD2ABZ

Thanks!

Fuel pressure is already ok, 1 week ago a brand new fuel pump has been installed.

GregD2ABZ

The service has already checked the fuel pressure, and also monitored it while driving and accelerating. It is at normal level, even at full throttle.

jfrahm

Well then maybe typical spark issues, I'd get some used coils and some ignition modules and give that a try. Or swap the coils and modules and see if the code moves to the other bank.

BerserQ

Guys, i need help. someone give me photo with crankshaft place on abz. i cant find it. ty.