mems fuel pump relay wiring

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mems fuel pump relay wiring

Postby Jin » Fri Mar 20, 2015 12:29 pm

Morning all
Please help, my car is driving me nuts and I’ve no hair left to pull out

1991 1.4 MPI GTI
Ever since I’ve had the car the fuel pump motor has been fed direct from the ignition switch in a rather dodgy fashion, ok so it works but not as id like it and I’d rather it had a relay - preferably the proper relay.
I changed the MFU for a known good one part number ending in 10 which is mean to be the proper one; I’ve also tried the later MFU part number ending in 70? both have the same effect - the relay just clicks repeatedly when it should be on - taking the MFUs apart they both operate the fuel pump motor switching the same contacts on the MFU multi plug anyway.
If I jump a positive feed direct to the MFU wire feeding the switch contacts o the fuel pump relay the relay operates just as it should, powers up for one second then runs with the engine running - great
The issue seems to be that the relay switching contacts only seem to be receiving 10-11v and its not being fed from the battery live like all other 3 relays within the MFU but being powered from the ECU?
The 2 fuel pump relay contacts in the MFU go through the multi plug - the grey and (brown I think) goes to the fuse box then pump, the brown and pink (feed in +ve) goes to the ECU, surely the fuel pump is not meant to be powered by the ecu? I can see the relay coil is switched by the ECU (which seems sensible) and the pin outs match with what diagrams I have found, but I would have thought the switched contact would be direct to battery +ve? .
The metro Haynes manual shows all 4 relays receiving battery voltage direct, and another PDF Haynes copy I’ve found online shows the fuel pump +ve being fed from within the MFU by the main relay and doesn’t show the pin that my relay receives power from at all?, but both MFUs I have connect the power in for the fuel pump relay to the ecu brown / pink wire.

I don’t suspect the wiring loom between the MFU sand ECU to have been butchered since all other wires match perfectly to the Haynes diagram including the 2 other +VE in feeds to the MFU
I could get around the issue by jumping a feed inside the MFU from main relay to the fuel pump relay +VE in which would work a treat – but obviously not how rover intended

The only conclusions I can come to is there must either be another type of MFU available that internally has the fuel pump relay connected direct to live either from the battery or main relay, or the fuel pump relay is indeed meant to be powerd by the ECU at 12V and I have some kind of internal fault?
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Jin
 
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