vojnar

Please Help,
I have an Audi s8 5.2 v10 07/2006 and the car sometimes starts sometimes it does not, otherwise the car runs perfectly.
I can start the car spaying starter fluid to the air intake at any time.
The conclusion is that either it gets
false air (too much air),
or it does not get enough gasoline (injection time is too short during start)
or the injections are "dirty"
The local dealer advice me to change the air intake manifold but before I do that I would need to test this further, since that part is $3k and its cast aluminum and I don't believe anything can go wrong with it unless inside, but I might be wrong.
If anyone could help me with the manufacturer reference for:
1. Air mass quantity:
-during idle
-during engine start
2. Gasoline injection time
-during idle
-during engine start
3. Suction vacuum air mass quantity
-during idle
Any help would be appreciated!
Thank you

SaltyIrishman

Definitely don't throw parts at it. Read the "Sticky" at the top of the forum, let us know where you are located in the world [you may have a local resource that can help], and get the codes pulled via VCDS.

Do a search on "won't start" or something of the sort and search by subject only and you can narrow down the results. Definitely don't trust the dealer to know what they are doing here as they'll throw expensive parts at it until it finally gets fixed, which could add up very quickly.

MP4.2+6.0

+1 Really need a scan here; entire cost of VCDS (for life) assuming you have a PC is just over 10% of the part cost for this wild guess dealer idea.

vojnar

Hi,

Thank you for your repy!

We have made readouts but reference values are not available.

If someone could give me values on (s8 5.2) for the the following codes on master and slave side, cold and normal temperature that would help me to trace the problem: (we want to option out mostly software problem where the injection timing is not open for enough time. Mine reads 76ms when it don't start)

2/3
Injection time during engine starting
(ms)

2/4
Air mass (g/s)

10/3
Throttle angle
(%)

10/4
Ignition timing (degree)

11/3
Intake air temperature (C)

140/2
Specified rail pressure (bar)

140/3
Actual rail pressure (bar)

1/2
Coolant temperature (C)

Suction vacum during start

Symptoms:
1. Engine will not start sometimes for weeks, but than starts 25 times an afternoon perfectly
2. When it don't start than I can start it with starter spray at air intake right away. We replaced blow by gas oil separator and with the new one and it did not start no more even with starter spray no more start (not enough air)
3. No faulty codes
4. Tank pump pressure good
5. Gasoline High pressure good, but before cranking it may build up to 80 bar
6. Replaced crank shaft sensors
7. When it starts it runs perfectly 290 km no problem, smooth etc, perfect idle

We come down to the following:
1. Injection timing is too low (software problem)
2. Air intake manifold inside broke (dealer said)
3. Injection heads are not clean enough

Please advice if you can.

Thank you,
Gabor

MP4.2+6.0

FWIW, I've read this a couple of times but really don't have a good or firm idea of the fix. The fact that it doesn't start except with starting fluid at times but then always does when you use it is pretty odd. It suggests in turn a whole bunch of things like many sensors, basic ignition, fuel pumps, etc. probably are not the problem.

I'm having trouble understanding what you posted. That looks like measuring block data for some motor parameters. We are looking for the fault codes (if any) you can get with VCDS in the engine module. Those are five digit codes. Are there any?

Meanwhile, my only current guess given no start at times with no starting fluid but consistent start with it would be a flooded (with fuel) engine. That may show no codes. Ether (starting fluid) can often overcome a flooded motor--been there done that on all kinds of small motor stuff. Maybe a small chance it is a critical sensor that is acting erratically too, but the fact it starts with ether seems to overcome that idea.

For now, I would try:

1. Using a couple of treatments of a good fuel system cleaner you add to the gas/petrol, for example Techron. If it is flooding, it is likely (multiple) leaking injectors. Cheap fix before getting deep in there to look at them is trying to clean.
2. changing spark plugs. May seem a little odd if issue is some fuel leakage, but I often find on small motors with starting issues where ether helps, a weak spark/dirty plug can be a contributing factor.

haggisuk

I logged the values on mine and saved it

Mister Bally

If the fuel treatment and spark plug ideas don't work; I'm going with crankshaft position sensor is faulty/ wire broken/disconnected/connector corroded.

However, this is easily verified by a diagnostic scan for fault codes.

If you are not using a genuine VCDS cable/interface from Ross-Tech, you are wasting your time and ours. Look elsewhere for assistance.

vojnar

Hi,

Thank you for your reply.
I tried 1. and 2. already

No faulty code are present.
It's not flooded because if we unplug the cooling temperature than the system thinks it's -30 degrees and more fuel injected and the car start right away.

I just need if someone could tell me how many milliseconds the injection needs to be open during Ignition at cold and warm engine temperature. Mine is open for 76 ms, but not sure if that is enough for the engine to start.

Thanks

vojnar

This value is in data block 2 and it is the 3rd value set (ignition timing)

haggisuk

I have already logged the measuring blocks you requested, it's that attachment in csv format, either import it to excel or open it from vcscope from the Ross tech install folder