Fuel pump will not run.

[lib]

Hi

I wonder if anyone has any ideas on this.

Yesterday I drove my 1986 911 coupe out of the driveway into the road where it stalled, I tried to start it, the engine was turning over but it would not run.

After some time spent checking I found the fuel pump was not working. If I fed it direct and it ran and the car started.

following many hours of tracing the circuit I found that the supply came from one of the relays in the DME relay. This particular relay is given a negative return through the DME.

What I do'nt know is what sensor tells the DME to activate the DME relay by providing the negative return to energise the relay coil.

I would be very grateful for any help on this subject.

Thanks lib..

[Loren]

You did check the fuse in the front trunk? Panel 1 (center panel of 10 fuses) fuse 3 -- should be 25A

[magcuda]

the speed sensor gives an AC voltage to the DME which in turn grounds the DME relay to power up the DME and the fuel pump.

common failure the DME relay, carry a spare! I don't know how many cars got towed in and started when they came off the rollback.

Edited January 5, 2007 by magcuda

[lib]

You did check the fuse in the front trunk? Panel 1 (center panel of 10 fuses) fuse 3 -- should be 25A

Hi Loren. Thank you for your response to my problem. Yes I have checked the fuse and it was ok but there was no supply current to the feed in side of the fuse.

Regards Lib.

[lib]

the speed sensor gives an AC voltage to the DME which in turn grounds the DME relay to power up the DME and the fuel pump.

common failure the DME relay, carry a spare! I don't know how many cars got towed in and started when they came off the rollback.

Hi Magcuda. Thank you fpr your reply to my problem. I have checked the DMI relay by feeding the windings separatly and both relays in the DMI relay do function and there is continuity through the contacts and out to the pins. So it is possible that the speed sensor is at fault. Would this be the sensor that detects the crankshaft is rotating? Or is there another sensor elswhere? although the engine does run if I provide a separate ground to the fuel pump relay that's inside the DMI relay.

Regards Lib.

[magcuda]

yes that is the sensor that reads the flywheel speed. did you try another relay?

they can look and test good but are bad, wish I had a dollar for every one I replaced.

to test the sensor you really need a scope but an analog volt meter set on AC voltage can give you a reading.

[lib]

yes that is the sensor that reads the flywheel speed. did you try another relay?

they can look and test good but are bad, wish I had a dollar for every one I replaced.

to test the sensor you really need a scope but an analog volt meter set on AC voltage can give you a reading.

Hi maguda Thanks, I will try that and let you know

Regards lib.