vojnar

Hi,

I have cleaned the build up based on this video on the audi s8 :

https://youtu.be/Ugh9vPz2Zd8







Reading injector signals with an ossilloscope from audi s8 v10





Cleaning audi s8 carbon buildup





Cleaned and retested injectors











Pressure washed air intake manifold audi s8 v10

vojnar

As I posted before it looks like the audi s8 v10 sometimes starts and sometimes not caused by a voltage drop at the injectors. Around 28 to 35 voltage.

The injector opening time was measured with an oscilloscope during cranking (engine start)

Any advice would be appreciated, where to look for bad ground connection or which relay that supplies the ecus.

Thank you,
Gabor




Low (faulty) voltage reading: 32 V at injector opening time signal





Correct voltage and injector opening time on audi s8 v10 (63.2V)

EHLO

Would you post close up pictures of the carbon buildup on the back of the intake valves and surrounding area?
Thanks.

MP4.2+6.0

On relay location:

Assuming it is the same as the W12 with the twin ECU's, you see both of them in the plenum area once you remove the trim covers. You will notice one is screwed down on top of a black plastic box--I think it is the one closer to the (USA/continental Europe) drivers side. Inside that box is the relay that powers the ECU's and most everything else around the engine electronics--very little else is inside that plastic box. IIRC you have to take out the other ECU (toward the passenger fender) to get the one out on top of the plastic box. You will run into a few security/antitamper small bolts/screws, but they can be removed with some normal tool work. If you want it to look "factory" afterward, some of the front brake shield bolts from newer models with Torx heads (like RS5) fit very well. BTDT.

The relay itself is a very simple one and not very expensive. To be clear, what that relay is not is some very complex pre-ECU era relay with lots of different contacts. It basically just takes a signal and then turns power to everything on, including the ability to keep power supplied to some of the after run circuits like water circulation if needed.

vojnar

Hi,

Here is what the solution was:

Under the air intake manifold the injector anchor bolt were audi but 1 mm bigger than what it suppose to be, therefore the air intake manifold could not sit on its bed correctly and the car got false air all the time, which made the computer send less gasoline to the engine, not enough to start the car.

We ordered smaller bolts and the car starts perfect now!

Thanks everybody

haggisuk

Do you think the bolts are original or has someone been in there and ****ed it up?

vojnar

They were original audi bolts, but they just were not the right bolts, not the ones that were suppose to be there. I assuming that someone did not put the right bolts back after working on it, but Im not sure what happened since I bought the car like this from Germany.

haggisuk

Good find, I bet your glad. A smoke test should have highlighted that for you sooner but you were in there and done a carbon clean too, so a win win either way.