Fuel pump cutting out.
Discussion
My Chimaera 4.5 has developed a curious problem. The fuel pump suddenly switches off, or at least that's what it seems to be doing. I can be driving along and suddenly the engine just dies. If I press the fob on the key just as you would when first starting, the pump comes back on no problem so it's working ok, it just likes to turn itself off for no reason. It seems to do this when the engine is hot as the problem generally happens as I am returning home from a drive. Is this a common problem?
There are many and varied reasons for the fuel pump stopping assuming that is in fact what is happening.
When you first switch the ignition on the ECU earths the fuel pump relay which in turn powers the pump. (fuel pump prime).
The pump/relay then goes off until the ECU sees a spark signal from the coil indicating the engine is cranking or running.
I'm suspecting this may be loss of the spark signal as this is produced by the ignition amplifier which are famed for hot failures.
Next time this happens watch carefully to see if the tacho drops rapidly indicating it has lost signal.
You could also set up a couple of test lights on the fuel pump relay.
• TL1 between pin 87 (2 wires White/Purple & black) and earth.
This will light when the relay is powering the pump.
• TL2 between pin 85 (Blue/Purple) & Pin 86 (White/green).
This will light when the ECU is telling the pump to run.
At Ignition on both should light then go out. At start they should both come on and stay on.
At engine fail if TL1 & TL2 stay on then the pump or its wiring are at fault.
If TL1 goes out but TL2 stays on, then the relay has failed.
If both go out and the engine is still turning then the fault is somewhere before the fuel pump relay.
There is a lot of talk about old relays but the original metal bodied relays are Bosch and very well made. I would trust them more than modern replacements.
Steve
When you first switch the ignition on the ECU earths the fuel pump relay which in turn powers the pump. (fuel pump prime).
The pump/relay then goes off until the ECU sees a spark signal from the coil indicating the engine is cranking or running.
I'm suspecting this may be loss of the spark signal as this is produced by the ignition amplifier which are famed for hot failures.
Next time this happens watch carefully to see if the tacho drops rapidly indicating it has lost signal.
You could also set up a couple of test lights on the fuel pump relay.
• TL1 between pin 87 (2 wires White/Purple & black) and earth.
This will light when the relay is powering the pump.
• TL2 between pin 85 (Blue/Purple) & Pin 86 (White/green).
This will light when the ECU is telling the pump to run.
At Ignition on both should light then go out. At start they should both come on and stay on.
At engine fail if TL1 & TL2 stay on then the pump or its wiring are at fault.
If TL1 goes out but TL2 stays on, then the relay has failed.
If both go out and the engine is still turning then the fault is somewhere before the fuel pump relay.
There is a lot of talk about old relays but the original metal bodied relays are Bosch and very well made. I would trust them more than modern replacements.
Steve
Thanks for the feedback. At the moment the problem seems only to occur when the engine is hot, when I have been driving for an hour or so. I can start the car and go for a short drive and everything is fine. When it cuts out all I have to do is press the fob as you do when turning off the immobiliser and the engine starts again so it's basically the immobiliser coming on which is, of course, the fuel pump turning off.
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