injector pulse stops

[gary4567]

Hi,
I wonder if anyone can help with a problem I have with a 1999 Audi TT 225.
Car was running normally but one morning just didn’t start after a day of being switched off. The car would turn over but not start.
The problem was traced to a blown fuel pump. The fuel pump fuse was blown and with new fuse the fuel pump itself was found not to be operating. The pump was removed and tested and found to have failed. A new fuel pump was fitted and a new fuel filter at the same time. The fuel pump can now be heard to operate.
Used VAG-COM and no faults reported from the engine system.
The car still refuses to start.
Spark checked and appears OK.
Flooding suspected so plugs removed and cleaned off. Engine turned over with fuel pump fuse removed to purge unburned fuel. Still no start.
Starting spray tried and engine started, ran for approx. 20 seconds while the starting spray burned, then stalled. Subsequently engine will restart but stalls after a couple of seconds.
Noid lights used to check injectors; they indicate injector pulse appears to stop after a few seconds. Looks like the computer is switching off injectors for some reason.
Tested with MAF disconnected – still no start.
Can anyone suggest what I need to check next?

Gary

[euroslap]

Have you got fuel to the rail/injectors and have you definately got a spark?

[gary4567]

Yes - I have definately got a spark. And fuel is reaching the rail because it will start and run for a couple of seconds before the pulse stops.

[kenney]

Hi Are you sure it is not the immo that is the problem now.

[gary4567]

I assume it is not the immobiliser as the engine turns over and starts (briefly). Do you know how I can check if the immobiliser is kicking in / not working properly?

[kite]

The Immob allows the car to start then cuts in after a couple secs.
Seems like your problem is the Immob.
Do you get a flashing key sign on the dash.

[Crasher]

Yes, that sounds like the ECU and dash have become unmatched-I have seen this on the TT. Start and stop is how the factory immobiliser works but it should leave a fault code on the ECU and dash.

[gary4567]

I don't get the flashing key. It just looks like normal - a solid car with key symbol for the first few seconds after turn of ignition key then it goes off. Also there is no fault code showing through VAG-COM.

I have also just investigated the fuel supply further. I have taken both supply and return fuel pipes off the fuel rail. Fuel comes out of the supply pipe i.e. the fuel gets as far as the rail but there is no fuel appearing at the other end (return end) of the fuel rail. I'm not being daft am I but the fuel should be flowing right around, shouldn't it? If so, then I guess that it is getting stuck at the pressure regulator? Any other ideas? Can the rail itself get blocked?

[Crasher]

The fuel should come out of the return rail when the pressure exceeds 3 bar, so the pressure supplied is not high enough. Where did the new pump come from? I think you should check the pressure of the pump supply, just because you have flow capacity doesn’t mean you have sufficient pressure.

[gary4567]

Thanks for your reply (and to everyone else) - sounds like some progress.

The new pump was brand new from the main audi dealers. I don't have a fuel pressure gauge here. I will get one but is there any other way to get an approximate test now? e.g. can you give me a sense of how agressively the fuel should be squirting out of the supply line - if I held it vertically how high would the spray go if it's working properly?

[kenney]

When you are checking the return pressure are you cranking the engine,or have you,just turned the ignition on?

[Crasher]

Are you insane! What mechanic in his right mind would suggest you evaluating the pressure of raw petrol by squirting it up in the air? Have you ever seen, heard and smelt a human being burning? I have and it is not nice!

[gary4567]

Kenney, I have checked with just ignition on and by cranking the engine - nothing comes out of the return of the fuel rail in either case.

Crasher, thanks for the safety warning but I wouldn't just squirt the petrol all over the place!

What I have now done is connected a pipe straight to the supply from the pump. So the pump is just pumping straight into a container along a clear pipe. With the ignition on (but not cranking engine) the pump does not activate at all. With the engine cranking the pump activates and there is a flow. I would say the pressure is not very agressive but I don't know what strength I'm looking for. Is there a way I can assess it without teeing in a gauge? What does the fact the pump is not operating when the ignition is on (but not cranking) tell us?

[Crasher]

You need a gauge, I would say it impossible to tell the difference between 1 bar and 4 bar (domestic water supply is around 1 bar) which is about what the pump is capable of delivering. Do you think the fuel filter could be blocked? Did you change it?

[gary4567]

Yes - I changed the fuel filter at the same time as the pump.