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S2 ABY Coupe, N reg just had a stainless steel exhaust fitted and now not starting!
No power to the fuel pump- is this a fault with the Audi immobilizer?
Power to the fuel pump is via a relay only when the engine is being turned over on the key. The infamous 'hall sender' behind the camshaft pully triggers the ecu to supply a feed to the relay to power the fuel pump. Check for 12v at the connector on top of the tank whilst the engine is being cranked on the key. This may eliminate the fuel pump not providing fuel. However the problem could be elsewhere too.
The infamous 'hall sender' behind the camshaft pully triggers the ecu to supply a feed to the relay to power the fuel pump.
This is wrong. The hall sender has nothing to do with energizing the fuel pump relay.
The fuel pump relay is energized whenever the engine speed exceeds 13 rpm, and engine speed is determined by the engine speed sensor on the flywheel, or rather by the time between two flywheel teeth.
Interesting PRJ- Can you suggest anything that I can check?
Pembo told you correctly what to do. He just got a small detail wrong, but overall his post was correct - you must check the voltage while cranking. The pump will never be energized with just the ignition on.
Can you bridge the fuel pump relay with the starter bridge and override the ignition in order to check the fuel pump and establish if the fuel pump relay is goosed - first port of call? move on from there...
Well, my guess is, the welding blew lots of fuses if the exhaust was welded in-place on the car.
You have to be careful what you weld on the car.
Checking the ECU for faults (or seeing if it can be connected to at all) would be the first thing to try.
Checking the fuse would be the next thing. If the fuses are OK and ecu does not respond to diagnostics, then you will probably have to send it to me...
Well, my guess is, the welding blew lots of fuses if the exhaust was welded in-place on the car.
You have to be careful what you weld on the car.
Checking the ECU for faults (or seeing if it can be connected to at all) would be the first thing to try.
Checking the fuse would be the next thing. If the fuses are OK and ecu does not respond to diagnostics, then you will probably have to send it to me...
These are unlikely to just randomly fail...
First thing should always be OBD diagnostics in case of a no-start. As checking different things, well let's say you might as well check the whole car
It's a relay pulling high current and the contacts fuse together!!! two minute test my friend. Bridge the relay and then move forward from there...it's quicker than packaging and sending the ECU to you...BTW what welding occured here to cause damage to occur to the ECU?
it's quicker than packaging and sending the ECU to you...BTW what welding occured here to cause damage to occur to the ECU?
I quote and add emphasis on what I said:
Checking the ECU for faults (or seeing if it can be connected to at all) would be the first thing to try.
Checking the fuse would be the next thing. If the fuses are OK and ecu does not respond to diagnostics, then you will probably have to send it to me...
So, please note, I did say that *ONLY* if the fuses are OK and the ECU does not respond to diagnostics does it need repair. How you deduced that the ECU should be sent to me instead of the relay being checked completely escapes me.
With that out of the way - I have fixed a few ECU's which were voltage spiked by welding on the car.
Originally posted by chezz
It's a relay pulling high current and the contacts fuse together!!! two minute test my friend. Bridge the relay and then move forward from there...
So every time you get a no-starter the first thing you go checking is the fuel pump relay?
I think you need to pay a bit more attention to what the OP and I wrote.
The OP measured the voltage without cranking the engine. So it is normal that there is no voltage. In fact this will be the case on every single S2 out there.
Why would it be more likely than a non-functional hall sender or blown motor fuse in this case?
In case of a non-starter emphasis always needs to be put on proper diagnosis, to prevent tons of wasted time.
Checking random things that may or may not have something to do with the car not starting is what I like to call the "headless chicken approach". I can give more than ten reasons why the car could have a problem starting, but proper diagnosis can easily single out the real reason very quickly.
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