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MG MGF Technical - Fuel pump supply - Electrical


I had a question posted on a fuel supply problem which I have now found out the following.......

The fuel supply relay on the replay module that is located behind the MEMS unit is going open circuit on occassions. I have changed the relay and the same thing happens. The coil of the relay is okay when I put a supply accross it as the relay contacts open and close as normal. The car will start sometimes so the relay is working. I think the problem is the supply to the coil for this relay is going open circuit. The problem is that it ends up in the MEMS unit so the issue could be this unit. Before I have to give up and take it to a dealer to fix does anyone know of any other component in the circuit that could cause the problem ? I have wired the pump straight onto the live side of the ign and the car is working fine. Any suggestions?????????????


David Law

I can't see anything between the MEMS & fuel pump relay in circuit diagrams.

I expect you'll have already doused all relevant connectors in wd40 and eliminated poor contacts?

As its intermittent you could stick with the live pump feed but hang a bulb off the mems feed (run it into the cabin) then you can see when its on/off and maybe be able to deduce something.

Your Dealer could run Testbook diagnostics on the mems but if you are out of warranty you will probably decide to stick with your 'fix'. and save a lot of money.

John Thomas

This sounds like the "issue" MG admitted they had to my dealer. When the wiring loom was wiggled near the cam or crank sensor (I can't remember which) the injectors would fire - if ignition was on.
MG took my car and replaced the mems and the engine wiring harness.

Thanks for the replies.

Can someone recommend a point in the engine area that is on the positive sde of the ignition switch that I could hard wire the fuel pump onto. At present I have ran a cable into the main fuse box underneath the steering wheel. I want to tidy up and shorten the cables.

Still looking for suggestions on what my problem could be. Thanks for all the help.

I would be worried about by-passing the fuel pump inertia switch for anything other than diagnostic testing, but ....
have you tried bypassing the inertia switch and relay ?
i.e. take a feed from the battery side of the inertia switch (brown) - note that the circuit also feeds the alarm ECU; then via a switch to the fuel pump (White/Purple).

If this is OK, then you could include the inertia switch in the circuit by taking the feed from the brown/grey lead, or exclude the inertia switch by short circuiting it.
Is it possible to measure the current in the relay coil when it fails (the black/purple lead to MEMS is probably best for this) ?

What colour lead are you currently taking the feed from ?



When I measured the voltage on the Inertia sw with the Ign off it was 12 V. This means that this supply is live all the time. I cannot use this supply to the pump as it would be permanantly on. Or I am missing something here ?

I don't know what color the supply is as I have taken it straight from a spare spade terminal in the fusebox. This is only 12v when ign is on.
Thanks for the advice. I may just bypass the inertia sw to rule this out but as I said it appears to be the coil feed to the relay that cuts off and drops the contacts on the fuel pump relay.

This thread was discussed between 07/11/2000 and 08/11/2000

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