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MG MGF Technical - MGF 97 VVC model - ignition coil problem

I have received this request from a MGF 97 VVC owner in Australia who is looking for some help. Perhaps somebody with VVC experience can help:

Dear Sir,

To explain a bit of the background, we live on the Sunshine Coast in Queensland Australia. My wife came home in the car with it running on two cylinders. Looking in the water tank there was some sludge around the inner section at the water level.

After discussion with the local MG pundits the assumed diagnosis was a blown head gasket. The car had just done 75,000 K’s. I stripped the engine down, and the old gasket did not look like the one photographed on your web site neither were the plastic dowels broken. I had the head checked and very lightly skimmed and I was advised less then 4 thou was removed, which from previous experience on other older MGs minis etc was very little. Engine rebuilt and full works manual rebuild instructions followed including refill with coolant. New timing belts and plugs were fitted.

Engine started and immediately ran on four cylinders; great cured the problem. Backed out of the garage to go for a run and it started running on two again. Found that two and three plug leads were not firing. Dual coils suspected and replaced with new assembly, a very difficult job when engine is fully assembled. Engine started and ran for a couple of minutes on all four then went back to running on two and again found two and three not firing.

I am now a bit lost as the works manual does not cover the wiring to the ignitions coils. It does not give you any idea of how to trouble shoot relying I suppose on a fancy computer to tell them what is wrong. I don’t have access to a fancy computer so I need to be able to electrically check the LT loom from the coil to the engine management unit. If that’s ok then I suppose it could be the EMU which I am certain is going to be very expensive. The wiring diagrams I downloaded from your web site did not show the ignition coil to EMU circuitry or wiring colours

Well Gentlemen that is my problem. I cannot believe this has not happened before, so if there is anyone out there who can render assistance to a me in my hour of need it would be greatly appreciated.

Accordingly I look forward to your reply.
With kind regards
Jim Stubbings

I have passed back the link to this thread to him.
Tony



Tony Thompson

Hi Jim,

I have a workshop manual on cd but I can't copy items from it.
I've looked at the circuit diagrams for your car and I've found this:

Coil 1 is connected to MEMS pin 25, with a White/Black wire.

Coil 2 is connected to MEMS pin 26, with also a White/Black wire.

Both coils are connected (straight through the relay module)to MEMS pin 27, with a Brown/Pink wire.

I suppose the voltage supply comes through the brown/pink wire to both coils and they are switched by MEMS through the white/black wires to ground.


I hope you can do anything with this.

best regards,
Arend Groen
Holland
Arend

Jep, it is.
I've also no sense about the VVC but the wiring online here
http://www.mgfcar.de/schedules/sb10.jpg
http://www.mgfcar.de/schedules/sb11.jpg
colour code and all the other.
http://www.mgfcar.de/schedules/index.htm

Over to another with better knowledge

Dieter

Sounds like a problem with the HEXFET switching transistors inside the MEMS-box.... If shot by a previous short-circuited coil or other accidental short they tend to overheat even with a perfect coilpack.
When these kind of switching transistors overheat they just turn off,after cooling they work for a while again. There are specialists out there that can open up MEMS and replace the broken part(s).
I guess Dieter have one picture how these transistors are grouped along the inner sidewall for extended cooling. Most of the "output" functions in the MEMS are switched by this method.Fuelpump,ignition,fans etc.
BR, Carl.
Carl Blom

This thread was discussed between 14/09/2009 and 15/09/2009

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