Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGF Technical - Fuel pump relay

I have a problem with the relay fuel pump on a P reg 1.8 MGF. The relay will not hold (I have tested it out of circuit and its okay)and it looks like the fuel pump relay drive from the MEMS unit is never active (pin 97) Any ideas ? Could this be a sensor or is it the dreaded MEMS unit ?
I have ran a positive feed to the fuel pump and the engine runs fine but I am trying to find the route cause of the problem. Any suggestions ?
David Law

Try looking at the wiring diagrams on Dieter's web page

Best of luck

Hmmm.. wasn't there a similar thread already ??

Can't recall exactly. But from my memory the Main Relay located under the ECU was the problem.

Could be total off topic, though, did you already try the Archives ?

Dieter Koennecke

As I read the circuit, the pin on the MEMS for the fuel pump should switch to earth for the relay to work. The other connection to the relay coil is via a white wire from the ignition circuit. So check white wire to fuel pump relay live with ignition on and black/purple wire from relay to MEMS is low volts or zero with ignition on.

Bruce Caldwell

Hi all,
I think Bruce is right exept from one thing. The black/purple only goes momentary to ground when You put on the ignition. This to "prime" the system just before starting. The flywheel has to turn before steady ground can be found on that cable. For security reasons the fuelpump only runs when engine turns. Inside the ECU are several transistors bolted to the casing (cooling). They are all "open collector" for the outputs. Normally they are very rugged and can stand both +13 Volts without any load in-between and other abuse. A much used one is LM395 that IMO is close to failsafe whatever happends. On SAAB and Volvo these can be changed - donīt know about the Motorola ECU for the "F" as I havenīt worked on one yet....
A small 12V lightbulb (3 to 6 Watt interior one ) inserted between freee black / purple cable and +12 Volt will light up if all is OK when You force the engine to run with blocked relay. If not probably the final transistor is gone....
Does MGR have a exchange system for ECU - units ??

Hope this is of some help, regards Carl.

>On SAAB and Volvo these can be changed - donīt know about the Motorola ECU for the "F" as I havenīt worked on one yet....

Nothing is impossible ;)
Though dismanteling the ECU is to recommend only if a clear failure got analized.

Dieter Koennecke

This thread was discussed between 28/12/2001 and 01/01/2002

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.