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MG MGF Technical - Current Drain

I've seen a couple of threads recently from people not being able to start or sometimes not being able to start. I've had the intermittent kind of starting trouble for a while until yesterday it just refused completely.
I got the AA out and they found that the battery was dead and wasn't holding a charge. The AA guy also tested the drain for me IE what the car is taking from the battery when its just standing there with everything switched off). This turned out to be 0.3 to 0.4 amps which is higher than the AA's recommended 0.1 amps.
Is this standard for the F? (i haven't got any fancy extras or obvious electrical problems)
The guy basically told me that its like leaving the car parked with the courtesy light on - which strikes me as BAD for a car that might get some well-deserved rest over the winter months.....

John Philpott

That certainly sounds like a significant power drain. The engine management system has a power delay system that keeps the purge valve open after the engine is switched off. The circuit remains live for a variable period after engine switch off- but usually no more than 15 minutes. Obviously, if there is a fault in the MEMS whereby the circuit remains active, this could lead to the power drain that the AA guy detected...

Check out the power delay circuit info that Carl and Dieter put together:


Rob Bell

Thanks Rob - the AA guy tested the drain fairly soon after engine switch-off so i'm hoping that I don't have a fault and that this can be explained by the MEMS delay and a dead battery (which had been dying for some time).

I'll get them to look at it next time it's in.
Thanks again
John Philpott

Common things being common, this is the most likely explanation. Fingers crossed John!!!

Rob Bell

Remove your lamp from in the boot and see what happens. Chances are it could be on when the boot is closed or even when the AA were there the boot was open.

By the way I'm talking about the one at the rear of the car, inside the boot lid.


Just tested my ageing battery with a gunson Testune Multimeter ... I did the battery charging test ie black clip to negative terminal and red to positive. Started the engine and got a reading of 13V which according to the scale (12V-13.5V undercharging, 13.5V-15V OK and above 15V overcharging) suggests there is a problem with charging the battery - possibly alternator fault.
Question if the battery itself is faulty will this affect the charging voltage applied to it - i would have thought not ??

The leakage was around 0.03A (interior lights off, boot and bonnet lights off) whilst the battery charge/ageing test more or less said the battery was a goner ...



Get down to EXEL on Burlington Road, they can do a full test and supply a new battery.

Very helpful spares shop as you probably already know.


I pass them every weekend on my way into Wimbledon (for shopping). Out of interest what makes (of battery) do they supply.


John Nottingham and
Anyone who can help.

My Saga so far which is still unresovled, but sounds very similar to your problems.

Purchased MGF 3 yr old from rover dealer in nottm oct 99 as a second carFOR sundays, sunny days ect.

No problems for 6 mths despite little use and long peroids standing. Then battery was too flat to start the car if left for more than 1 week. Had the charging system checked out all ok. Decision at that time was that battery was over 3 yrs old and could probaly not cope with car being left standing for one week at a time. Replaced battery everything fine for six months and same thing starts to happen.

At this point I suspected that something was draining the battery. Disonected boot light and bonet light. Problem still persists. Decided that it may be a possibility that my new battery was faulty, so got it exchanged. Problem ok for about 4 weeks although the car was not standing for more than 3 days.

Problem now returned.

Can anyone help! Now reduced to disconecting the battery or charging.
Something is definately draining the battery.
Battery is absolutely flat now after only 3 days.
Local Dealers not aware of what the cause may be.
Problem is getting worse and initially was very intermittent
Car starts fine when battery is charged.
When battery is flat and the battery charger is connected a whirring noise comes from the engine compartment which lasts for about 5 seconds.

Would appreciate any comments that may help. From some of the bulletins I read it appears that some peaple may be experiencing a similar fault.
Martyn Unwin

The regulator in the alternator should control the voltage between 13.5 and about 14.5 volts, engine revs are not that critical above about 1500 to the voltage.
Assuming the test meter is good then if you are getting only 13 volts then I guess the alternator will require changing and not the battery.
Stuart Elliot

Martyn - there's two threads in the heading "battery...". Sounds like you may have the realy problem that I think is afflicting me too.

an easy check is to remove the second fuse in the under-bonnet fuse-box (this feeds the MEMS relay box), and see if the thing is still draining. Always supposing you've easy access to a jump-start or a battery charger, of course.

It's not an expensive fix if it IS the relays, you'll be pleased to know. but check the archive - the guys have explained it much better than I.

Ed Clarke

Hi Martyn,
You mention a "whirring noise" whenever reconnecting the battery or charger. This could IMO be the stepper motor that controls the amount of air -bypass around the throttle. This gives a good indication of Your MEMS ,(computer) never shuts down ! Either direct MEMS related fault OR MEMS relay module fault. See archive for more info.. Any competent garage with Test-Book computer will solve this in no time !

Best of luck , Carl.


Not to sure about the brands, but certainly a various number of various performances, 1/2/3/5 guarantees, standard, heavy duty etc.

Halfords is just across the road so you can always compare.


Ed & Carl

Many thanks for yor help.
Removed the Engine management fuse (No.2) and hey presto. Car stood for 3 days and no flat battery. From what you guys say problem may be either mems or relay.
MEMS sounds expensive and I am not sure exactly what it is.

You mention that you think you may also be experiencing a similar fault and if the relay is at fault then this is not to expensive. If you have managed to get yours fixed would appreciate an update and approx cost involved.

Thanks again for your input
Martyn Unwin

Martyn - I'm pretty certain that if you only remove fuse 2 then it is a relay problem - if the MEMS was keeping the relay open removing fuse 1 would stop it. Need to check wiring diagrams to be sure.

I believe the relay box costs about 30, but don't have a part number... some kind soul around here will know it, no doubt. Haven't fixed mine yet - lack of time, so I'm still resorting to fuse removal when I leave the car for longer than a few hours. It's also possible to replace the individual relay that's causing the difficulty (less than 5), but that's a little more faffing about.

Ed Clarke

This thread was discussed between 02/04/2001 and 11/04/2001

MG MGF Technical index

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