Shaking engine, car stalls - error codes

gti69 · #1 24th January 2015, 04:48 PM

Hi guys.

Yesterday my A8 would not start, basically after turning the key nothing would happen. I had similar issue before but back then after a couple of minutes it would start no problem.

Today I got to the car with a charged up battery as I though maybe the voltage is too low, had some problems with alarm turning on randomly so I though the battery went flat a bit. Before hooking up the replacement battery I tried starting the car again and it started no problem. Jumped in and wanted to drive away but the engine started shaking and the revs started to go down until the engine stalled. Started it again no problem, kept the foot on high revs for a few seconds but it started shaking and dying again. After a couple of tries, now after starting it just shakes and would stall in 10-15 seconds.

Hooked it up to vag com and the below is the list of engine codes. Any idea what it might be? Seems like it is one side of the V8 engine. Your help would be much appreciated.

Control Module Part Number: 4D0 907 557 J
Component and/or Version: 4,2L V8/4V MOTR AT D01
Software Coding: 04263
Work Shop Code: WSC 00000
5 Faults Found:
17740 - Knock-Control: Cylinder 8: Regulation Limit Exceeded
P1332 - 35-10 - - - Intermittent
17739 - Knock-Control: Cylinder 7: Regulation Limit Exceeded
P1331 - 35-10 - - - Intermittent
16500 - Engine Coolant Temp. Sensor (G62): Implausible Signal
P0116 - 35-10 - - - Intermittent
17737 - Knock-Control: Cylinder 5: Regulation Limit Exceeded
P1329 - 35-10 - - - Intermittent
17738 - Knock-Control: Cylinder 6: Regulation Limit Exceeded
P1330 - 35-10 - - - Intermittent

Thanks.

Tom

PsYcHe · #2 24th January 2015, 06:17 PM

Could be something more sinister, but pretty sure your engine has the ignition amplifier units. They look like little black boxes attached to the front of the engine with wires coming out to the coil packs. Swap them over and see if the problem moves.

gti69 · #3 24th January 2015, 06:33 PM

Ok, thanks for this. I will go over in a bit to have a look. Car is sitting ca 15mins walk from my house

ainarssems · #4 25th January 2015, 06:04 AM

I don't think it will be ignition amplifier, faulty ignition amplifier normally result in misfire fault codes and usually only 1 or 2 cylinders not all 4, addition to this each ignition amplifier controls 3 cylinders on each side, not 1 side each. If I remember correctly 1 is for cylinders 1,4,6 and 7 and the other one for 2,3,5&8.

Now to the knock control fault codes, first lets understand how the system work. There is a knock sensor on each side of engine which measures 'knock' or speed and violence of the explosions in the cylinders. If the combustion is too fast/sharp ECU retards ignition timing a bit at the time until combustion speed is normal. If it gets to the point where it has retarded the ignition timing as far as it can and it's still knocking it will throw up error code.

The reasons why the knock occurs are:
1. Too little fuel (or too much air if you look at it the other way)
2. Poor quality or octane fuel
3. Overheating
4. Large amount of carbon buildup in combustion camera.
5. Faulty knock sensor
6. problem in wiring
7. Or it could be false alarm if you have loose bolt, nut or whatever knocking on the engine.

It only shows the error codes for 1 bank of cylinders but it could be an issue that affects both banks but because of slight differences one might be just over the limit to bring up fault codes and the other one just under.

Considering that the car stalls in the short while after being started I would look at the fuel supply first- amount of fuel in the tank,fuel pump, filter, pressure regulator, relay.

Have a look at measuring blocks 13,14,15 and 16 on VCDS to see if ignition timing gets retarded for one bank or both, that will show you if you have issue that affects both banks or only one. And then you can explore options depending if it's 1 bank or both.

gti69 · #5 25th January 2015, 11:05 AM

Thanks guys. I did swap the ignition control units - the car would run as rough as before and I was not able to tell which cylinders were affected after swapping. Error codes are now no longer appearing after clearing them but the car still runs rough and dies. If I leave only one unit connected at a time, car will only start with one of them so my idea was that it might be actually it.

Having also posted on Polish A8 forum, http://www.a8team.pl/, guys in there are saying this is a fuel pump problem and it should be replaced. Could that be the case?

Will check the measuring blocks later on today.

Cheers.
Tom

gti69 · #6 25th January 2015, 11:30 AM

On another note, if this proves to be a fuel pump problem, had anyone used aftermarket replacements and can comment on them?
Cost on ebay:
replacement pump (aftermarket) ca £40
replacement pump (eurocarparts) ca £95
replacement pump (genuine VDO) £125

Costs on polish 'ebay' allegro
replacement fuel pump (aftermarket) ca £30
replacement fuel pump (genuine VDO) ca £90

Thanks,
Tom