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MG MGF Technical - VVC Starting problems

I have received a letter from an MGF owner with a problem - he doesn't have internet access (no, thats not the problem) - wonder if you guys can help:

My 1999 VVC will start brilliantly if started from cold but if switched off and re started after anything up to 1/4 hour it takes up to 10 secs of cranking.

The following sensors have been changed:
Cranks sensor
Air temp sensor
Oxygen sender
Water temp sensor

Testbook reveals that there are no faults logged. The fuel pressure has been tested and is OK.

Any ideas?

Some extra info not in his letter:
I know that the car has been to 2 dealers and to Brown & Gammons and all are baffled. The Cat is now trashed (but I don't think it was when the problem started).

I know that there is a potential problem with starting if a cold engine is switched off before it goes through its warm up cycle - but this fault occurs on a hot engine. Said owner dreads stopping at a petrol station coz its a bugger to start the car afterwards.

Thanks in advance

Sounds like: either the spark plug gap is too narrow, or the coil is faulty (coils like to fail when their hot). Have seen the same problem in many cars, and these two faults caused most of them.

With an MPi I'd put an oscilloscope on the king lead (with #1 pluglead to sync) - this would show all 4 spark plugs firing (or attempting to). A VVC probably needs a dual beam scope (one per coil). The old-fashioned Sun/Crypton tuners used to have specialised 'scopes for this.

What state are the plugs in after it fails to start ?
I would expect them to be soaked in petrol (from the description) ...



Sounds like a classic case of leaking fuel injector(s). No problems starting cold because any leaking unburned fuel in cylinders will have evaporated, but on a warm/hot restart any new fuel comming in will over flood the engine as it is already flooded with leaking fuel. Causes long crank times on a hot engine often times followed by a rough/stumbling running engine until the excess fuel is burned and plugs clear up. Left uncured causes catalyst damage and engine bearing damage. Have your shop check for risidual fuel pressure after ignition off. Depending on the fuel system used( I'm unfamiliar with MGF) they might have to block return line. It should hold pressure for a specified amount of time unless your injectors are leaking. As others mentioned checking on scope while the engine refuses to start will narrow down your search. Good luck.

fuel injector/fuel pump problems are very prevalent in US GM's, and are frequently the cause of numerous intermittent problems. On UK spec cars the fuel injector systems are not normally the first attack point, being a bit more reliable for some reason. I have found when the testbook (Scanner) shows no faults, it's normally an old fashioned spark plug/spark plug lead/coil problem, not an ECU sensor.
Combine this with the unrealistic life expectancy of the MGF spark plug, poor quality spark plug leads, and I think this will frequently be the answer.
If the MGF's were driven long miles on spacious empty freeways, the spark plugs may last their predicted life: however the MGF revs high, runs hot, and there a lot of stop/go driving done here. I use mobil one, and change it and the filter mid-service interval myself; 12000 mile/12 month services are too long for me. 72,000 miles for spark plugs; well I know there good spark plugs, but 72,000 miles seems a bit optimistic.

By the way, I've been working on a Bonneville SSE for the last month, curing odd performance problems; needed all the fuel injectors replacing, new fuel pump, coil module, and crank case sensor; and it only has 73,000 miles on it.

Crank sensor?

Crankcase sensor, the US GM's also use a Camshaft sensor as well.

Thanks for your help.

Fuel pressure has been tested and its OK and doesn't drop. So the injectors are OK.

Going to investigate the coils. DrDave - the crank sensor has been chnaged and it didn't help.


This thread was discussed between 08/03/2002 and 11/03/2002

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