Audi Coupe Quattro running very rough

[James Pheby]

Hi everyone,

I recently bought a coupe, and it was working beautifully initially. As its a high mileage and not recently used car, I decided to service it. New Oil, Oil Filter and spark plugs were fitted, and a mis-matched fuel filter almost went on, but was wrong so couldn't be fitted. After this minor service, I have a very annoying problem...

What I have occurring is that the car starts fine, but after around 5 to 20 seconds, there is a rumble which sounds like a mis-fire and a severe lack of power which progressively gets worse until the car stalls. If the accelerator is pressed anywhere between 1/4 of the way and fully down, the engine seems to increase in rumble-intensity when pressed around 1/4, or stop firing altogether and almost stall when pressed 1/2 way down or more; the inevitable stall can be prevented by releasing the throttle a decent amount if this occurs. Quick bursts of the throttle show an initial delay in engine speed increase, but it does speed up.

What I have checked:
I have changed the fuel pump now, as the original old unit was very noisy, and I figured it was causing issue. A direct electrical feed has been used to ensure the supply is not the problem to it.
A new fuel filter has also been attached, along with new hoses around that area.
HT Leads have been removed 1 at a time, and each one causes an noticeable misfire when removed.
Breather Hoses have been checked/replaced
Electric Multi plugs have had a thorough blast with contact cleaner and corroded spades replaced.
Old spark plugs been re-fitted
On a side note, the cold start valve does not send fuel when the engine is cold :S


Current thoughts to the problem are:

• The fuel system needs to be bled somehow - anybody know if this is a known issue?

• The vacuum hoses from the rocker cover are incorrectly fitted or damaged
• Some demon electrical fault...

Any suggestions would be GREATLY appreciated. Thanks a lot in advanced!

[size12]

Year engine and model would be very handy for anyone within to help.

Sounds like fuel starvation, could be injector filters blocked or a vacuuming fuel tank.
Does it run with fuel cap off?

[James Pheby]

Its a 1988 coupe quattro, with the KV 2226cc n/a engine.

I will try the fuel tank with no cap tomorrow. However, when I have removed the cap after running the engine there has been no sound of suction of air.

[scotty33]

Carefully check the ribbed 'igloo' intake hose for splits etc., a vac leak here can cause an increase in airflow WITHOUT a corresponding increase in fuel. Also check the air metering plate is not sticking?

[James Pheby]

Progress so far: We removed the injectors, and placed each one into a beer bottle of the same size. The pump was then wired up directly to the battery, and then the metering plate was pushed. Only fuel came from number 1 injector constantly, but the others only occasionally jetted - I am right in thinking they should all jet equal amounts all the time while the plate is open? I have now removed the Fuel Distributor to back-flush and clean the system and will test again, along with the pressure.

[scotty33]

I think there's a possibility the injectors themselves are also 'tired' the 'jetting' you mention should really be more of an 'atomised cone' pattern I think. But yes should be continuous.

This might help:

http://www.cis-jetronic.com/public_doc/07.3-0997-06.pdf

[James Pheby]

Phew! Success at last
I blew out all the injectors, injector lines and the distributor and cleaned everything as well as inspecting the relief valve.
When i did the same test after reinstalling everything, each injector squirted out equal amounts and in a nice fan.
And when i put the injectors back in, the engine purred away like is should.
Thanks for your help guys. Im sure there will be another question about somthing else soon...