GOLF AUTOMATIC

[mondial]

No response last time, but surely worth another try.
I have bought aN "M" reg Mk11 Golf automatic. Ir runs beautifully and starts on the button, as it were, running on all cylinders. But it cuts out after literally one or two seconds. It then restarts immediately and does the same again. This may happen 4, 5 or 12 times before it finally runs perfectly. This behaviour is irrespective of wheter it is the first time of the day, or after a journey of any length, whether it is fine or wet. Any ideas?
HELP!

 

[Simannjo]

Are you able to keep it running by raising the RPM using the throttle? Yes indicates a possible problem with idle control system; No suggests ignition system or fuel delivery...

 

[mondial]

When it fires up, which it does easily, it stops after only two or three seconds, whatever I do. If I use the accelerator, then on starting it runs up to the relevant revs and then dies in the same way. It does not happen every day, maybe once or twice a week. Maybe just in the morning or maybe every time I stop start on a day.
David

 

[Simannjo]

The fuel pump (I assume petrol) is controlled via a system that needs to know the engine is running so as not to pump fuel if the engine is not running. An ignition signal is usually used via the ECM or a separate relay on earlier systems. Upon startup, the system is overruled to aid quicker starting, but an ignition 'signal' needed after a second or two. If the ignition signal is lost then the fuel pump will stop running after a few seconds of starting - Engine dies.
Try this. Turn your ignition on without starting the engine, You should hear a faint hum from under the back seat - you may have to get very close to the tank. The hum should sound for a few seconds only.
See if you can hear the fuel pump running before starting the engine, also when starting the engine and when the engine is running. It will be working throughout all these conditions but may be difficult to hear.
When your fault occurs - Can you hear the fuel pump running?
If you are losing the feed to the fuel pump from the control system intermittently then the symptom would be as you describe.

 

[mondial]

I appreciate your help and will try what yuo suggest over the next day or so. It may be a few days before the fault occurs. If it is indeed the signal not getting through to the pump, then what is the cure?

 

[Simannjo]

Just to clarify... The fuel pump is given 12 volts by the fuel pump relay. The relay may control itself by receiving an 'engine is running' signal or the relay maybe controlled by an ecm. Either Engine Management or immobiliser.
Sorry if it all sounds technical, but the key is to learn as much about what is happening as much as what isn't.
You have a very difficult problem for anyone to diagnose and information on the 'hum' will help build a picture for successfully resolving intermittent conditions (which are a NIGHTMARE!!!) EG if the hum is always there, then it is likely to be an ignition problem.
Cures range from a broken wire costing pennies (once found of course) fuel pump relay for around a couple of tenners, ECM for a whole bunch of 'em.
Depending on competence, it is possible to temporarily provide the fuel pump with 12v when it is faulting. to confirm the cause of your symptom.

 

[Simannjo]

Just to clarify... The fuel pump is given 12 volts by the fuel pump relay. The relay may control itself by receiving an 'engine is running' signal or the relay maybe controlled by an ECM, either Engine Management, (which already has it) or immobiliser.
Sorry if it all sounds technical, but the key is to learn as much about what is happening as much as what isn't.
You have a very difficult problem for anyone to diagnose and information on the 'hum' will help build a picture for successfully resolving intermittent conditions (which are a NIGHTMARE!!!) EG if the hum is always there, then it is likely to be an ignition problem.
Cures range from a broken wire costing pennies (once found of course) fuel pump relay for around a couple of tenners, ECM for a whole bunch of 'em.
Depending on competence, it is possible to temporarily provide the fuel pump with 12v when it is faulting. to confirm the cause of your symptom.[/quote]