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MG MGF Technical - Engine cutting out - Fuel supply ?


My 1996 MGF 1.8i cut out and came to a halt. It started again but same thing happened. When I check the fuel supply line just after the filter no fuel is pumped up while cracking the engine. I think I may have a faulty fuel pump. The problem is that sometimes the car will start and fuel will be pumped and the engine run ok but it cuts out after a time. Any ideas of what the cause may be and how to solve it ? I am hoping it is not the engine management unit !
David Law

The MGF fuel pump will wear out faster if you always wait till the reserve line on the fuel guage to fill up because the pump is of the in-tank type. It needs fuel to cool down while doing its function. The engine cutting out after a time, either idle or when driving, is a symptom of a faulty fuel pump.

By the way, when did you change your fuel filter last? It might be that the fuel filter is clogged.You may want to have a look at this first as it's a cheaper option.

I echo John 's (NZ) posting. Check or even replace the fuel filter first (they're cheap!). I siphoned 10 litres of petrol out of one car I had thinking the petrol was the cause of a engine that wouldn't go. I was pointed to the fuel filter by an AA man. 6 later the car was running again.


It could also be a MEMS fault - with these modern cars you need the various bits of test gear. I suggest you get a MG dealer to check it out.

Ted Newman

Thanks for the info. Does anyone know if there is a Haynes manuel for the MGF available yet ? I need to try and find out where the petrol pump is situated and get access to test it.
David Law

No Haynes as yet!

The petrol pump is in the petrol tank which is mounted behind the passenger seat (UK Model) and you gain access to it from under the engine cover.

Ted Newman

Once you have the engine compartment cover off, you then need to remove a circular cover (held by 4(?) bolts), as Ted says - behind the passenger seat.
Note which fuel pipe attaches to which outlet/inlet on the pump !
You should disconnect the battery, and remove the pressure from the fuel line - you can do this by removing the fuel line from the fuel filter - but if you are looking at the pump you probably already know about the filter, etc.

Good Luck

Be careful if you do remove the pump -its attached to the (easily damaged) fuel guage sender. I had one replaced under warranty - the pump costs about 200! As has been said I'd try replacing the filter first if you think its a fuel pressure problem and check the electrics as it doesn't sound like a fuel fault.

Thanks everyone.

After a long weekend I have found out it is not the filter or the fuel pump. The electical supply to the pump is intermittant and cuts out now and again. I have rewired the pump temporary to the ingintion and this has cured the problem. I still don't know what the root cause is. Does anyone have an electical wiring diagram or know what route the fuel pump cable (white and purple on my car) takes ? I have traced as best I can and it does not appear to go directly into the EMU. Does it go to another component ? A relay or something ?

David Law

If it's supplied from another source succesfully, then I guess the earth is OK.
The White/Purple supply lead goes to a relay - I think this is in a group of relays, hidden behind (ie against the bulkhead) the MEMS ECU. The relay switches a supply (now in brown/grey) from the inertia supply switch (at rear/left of engine bay) - and this is supplied by a brown cable from Fuse 2 in the Under-Bonnet fusebox. The switch signal for the relay is supplied via a white cable from fuse 14 in the passenger compartment fusebox, switched to earth by the MEMS ECU via a Black/Purple cable.



Thanks for the help. Are saying I have have a faulty relay ? Or are the relay contacts inside the engine management unit ? Under normal operation when the ign switch is on the punp runs for 5/6 sec and cuts out if the engine is not started. This does sound like a timer relay that is faulty. Can you describe exacly where it is in the engine compartment if you know ? Many thanks. PS How come you know so much anout the car ?

David Law

There was a copy of the wiring diagrams out on the WEB somewhere (but I can't remember/find where at the moment).

If you search the MGF Technical Archive I'm pretty sure you should be able to find the URL.... Alternatively if you published an email address, someone might mail you to tell you where it is.


I'm not saying your car has a faulty relay (though it's possible) - I'm just giving the wiring details for the fuel pump from the Rover wiring diagrams. I don't know much about the car, but I can read a wiring diagram !
To get to the relay unit (it contains 4 relays), you need to unbolt the MEMS ECU from the bulkhead on the LH rear bulkhead (of the engine bay). Unfortunately, modern connectors make diagnosis very difficult - I would love to have a 'break-out' box for the MEMS connections.
Now the pump is supplied from the ignition can you put an LED (or similar) into the old supply so you can monitor it ?

Have you had the car from new ?


Thanks again. Yes, I have had the car from new. I will take your advice and stick an LED or 12V lamp accross the old supply to monitor it. I wish I knew what component sets the time for the priming of the fuel (4/5 secs at ign) as I am sure this may be the cause. Maybe someone will respond with the address of the wiring diagram. This would be a great help. Thanks for all your replies. I am getting somewhere slowly ! Other than this problem the car has not failed me once so I guess its not too bad.
David Law

Hi David,
1. It is the MEMS -unit that both gives the initial priming and keep fuelpump running continously when engine is at speed.
2. There is a crash-breaker =inertia switch as described in manual that can making bad contact. Depress the rubber button on that one just in case.
3. The main voltage to the pump goes via "Fuse 2 ,30A"
placed under bonnet. Chech that one.
4. Fuelpump is activated thru said relay in "Relay module" close to MEMS in engine bay at the left side.
It is possible to make the fuelpump run by energizing that relay. To relay module goes a Black /Purple cable. If You have a cable with a needle connected to good ground (chassie) and punctate that Black/Purple cable the pump will be forced to run when ignition is on.(Taking this cable to ground is actually what MEMS does when all is OK. There is no current comming from MEMS itself so it is safe to make this test )
5. If the pump refuses to run as a last resort check
"Fuse 14 , 15A " located in passenger compartement fusebox.

Good luck , Carl.

And if all seems OK with fuel-pump cheeter test and You still have difficulties starting it could be that crancshaft-sensor , a well-known candidate for troubble... This item is the one that tells MEMS that engine is turning = start continous running of fuel-pump. That sensor is well covered in another running thread....
Regards , Carl.


This thread was discussed between 18/10/2000 and 23/10/2000

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