9x8

Hello everyone, a friend of mine is looking for assistance.

The car is 1991 S4 with automatic.
Symptoms are following:
A couple of months ago he tried to start the car to go for a short drive, it started okay, but almost instantly died. The re-start showed similar behavior. All later attempts didnt get her running even for a moment.

What has been checked:
1) Fuel pressure seems to be okayish, at ~50psi.
2) Injectors seem to be clicking normally while cranking, also it looks like spark plugs are wet if taken out after a few starting attempts.
3) LH is a rebuilt unit, but we swapped both LH and EZK from my GT to check anyway - no go.
4) There is spark, and it seems to be travelling between cylinders (checked on 2 cylinders actually).
5) Timing belt looks intact, all the timing marks match.
6) Flex plate has been released ~5 000km (or ~2 yrs) ago.
7) Tried different MAF units, tried even disconnecting it altogether.

Basicly we're running out of ideas, what else can be checked?
Thought about CPS, but then we would have no spark if I understand correctly?

ammonman

Pull the vacuum lines off of each of the fuel pressure regulators/dampers and smell the end of the line. If there is any fuel in the vacuum line or fuel smell from the line you have a bad diaphragm in the damper or regulator. This floods the engine with fuel via the vacuum lines and doesn't get enough air to start unless the throttle is held wide open and the car is cranked long enough to clear the excess.

Mike

FredR

1. Pull the spark plugs- make sure they are clean and dry. When wetted they can take an age to vaporise strange as it sounds.
2. To test the fuel regulator/dampeners pull the vac connectors off and press your thumb onto the male connector on top of the units- smell your thumb for petrol. Doubt this would cause the unit to not fire but you will sure get fuel in there that could wet the plugs.
3. Maybe there is a problem with the idle stabiliser valve. If this is shut you will be putting in fuel and no air - thus wet plugs. When you try a start with dry plugs- open the throttle very slightly to allow some air to pass the main throttle. If the engine fires up and immediately stops upon releasing the throttle pressure chances are it is the idle stabiliser sub system where the problem is. This may mean that either the valve itself or the electrical connections to it are down. Also check that the throttle switch is working correctly. I cannot tell you the terminal numbers off hand, but functionality of the throttle switch can be checked by continuity meter over the correct terminals on either the LH or EZ units. The throttle switch has two sets of contacts- idle and full throttle. If the idle switch is down it may be fooling the brains into thinking the engine is not at idle- not entirely sure on that one- I cannot remember if the contacts are open or closed at idle but if it does not change then the switch is toast .

Regards

Fred R

Landseer

Jumper the LH relay

9x8

Thanks for all the suggestions.
We did some more testing this weekend.
Dampers/FPR seem to be okay, no gas leaks.

Now, there is this weird thing: with LH disconnected completely - the car actually starts and runs for a couple of seconds (while there is fuel from previous starting attempts), then surely stalls. But with LH connected it doesnt start at all, it looks like there's too much fuel (or not enough air?).

So, basicly this means that all mechanicals are okay, that spark is produced properly, the problem is either fuel or air. Does this sound like bad (sticking) ISV?
Will try spraying some WD40 in there, I guess.

WallyP

As suggested, try cranking with the throttle held partially open.

AO

Sounds like it's flooding. Do as wally suggests. Actually, I'd suggest holding the pedal all the way while cranking. Might take a bit, and best to do it outside as there will likely be a huge plume of black smoke when she catches.

9x8

Well it looks like the issue is resolved, thanks for participation.
It really looked like sticking ISV - had to dry it out thoroughly and then start and run with pedal pressed almost all the way for about 2 mins, afterwards it smoothed out (ISV unstuck?) and seems to start properly now.

ammonman

My '90 would occasionally exhibit hard starting that would require holding the pedal to the floor while cranking. Once started, the problem would not repeat on the next start. It seemed to be a random occurrence over the course of a year before one of the fuel regulator/dampers went bad completely.

Mike