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 - mgf wont start when engine warm

Have just bought a 1996 mgf vvc and it runs great but seems to have a problem restarting when the engine is warm,have changed the fuel temperture sensor but has made no difference. Sometimes it starts when warm but other times engine wont turn over,or if it does it cuts out then I have to rev the accelerator to keep it running. When driving it runs great with no problems. Any ideas have seen this posted numerous times on internet but no one says what cured it!!
m kennedy

Could be a bit of lots of things. If the engine won't turn over look at the battery: charge level, terminal conditions, earth straps(the one from the engine to the body as well as the obvious battery to body) and starter motor connections. The general symptoms you describe are weak spark - a part of which might be the battery points above. You could then look at the distributor cap and rotor arm for starters. HTH

Thanks for your reply..doesn't have any problems starting from cold is just as if not firing when engine warm, car runs perfectly once running no misfires etc. Has just had head redone all coolants normal etc
m kennedy

Charles is right about the items to check first. Because you say the engine often won't turn over when warm and doesn't tickover properly when it does start, it sounds like you have two or more problems:-

a) Regarding not starting one of either the starter/solenoid, starter connections, battery or earth straps could be duff (I had a BMW that got heat soak into the starter and would never turnover until stone cold - changing starter cured it).

b) Regarding on (eventual) starting from warm you say it won't tickover without applying the throttle but it doesn't misfire. This sounds like throttle position sensor or a fueling problem. Take out a spark plug and observe tip colour - stong white coffee colour is good, white is weak mixture, black is rich mixture. The TPS can be reset to default (search for howto in this forum) or perhaps the ECU is erroneously controlling a weak fuel mixture after detecting false readings from the Lambda sensor in the exhaust manifold. Check the Lambda sensor wires (two white, 1 black one grey) haven't shorted out on the manifold, 'cos during head removal these wires will have been disturbed.

J Lennon

Thanks for your reply will check out the lambda sensor and the TPS. The car has now started kangarooing as well but not all the time. Did it once from a cold start and once from a warm start!!
Have bought another MGF as need something reliable for my work but still have to try and solve the problem as I now need to sell the faulty car and wouldn't want to sell a faulty car to someone else. So if the kangarooing enlightens the situation (ie fault find) then all help gratefully received. Many thanks once again.
m kennedy

Good decision to buy another F, one is hardly enough. Does 'will check out the lambda sensor and the TPS' mean that you have already thoroughly checked out the simple electrical things I mentioned with a meter? The brown temp sensor might have been an issue if the car had trouble starting when cold.
If it won't turn over as previously reported, the most likely culprit is simple electrical. If all of that is checked and you now get kangarooing, and the plugs all look clean, try the HT leads shorting out to cam cover mounting bolts.

Thanks for your reply once again, have bought new set of HT leads today and will then check the plugs as well all other electrical things have been checked and all working fine will let you know how get on once changed the leads, and will also check the Lambda sensor.
m kennedy

Have changed leads,changed plugs and lambda sensor. The car is still having problems starting when warm,it will start but runs lumpy then just cuts out but not all the time and when it does start it will be at 1200 revs and takes a while to settle back to 800 revs,then it starts running normal.... sometimes the car still starts from warm no problem
m kennedy

At one point, you said the car won't turn over - which had us all thinking you had an electrical fault - possibly a bad earth. By the way, there's an earth strap on one of the two bolts securing the gearchange cables bracket to gearbox. From the rear of the car, look left of centre just inside the subframe. However you've not repeated news it won't turn over, so must assume the problem is:- won't always start from warm or does, but runs lumpy.

VVC's don't use a distributor so it can't be the rotor arm. You've renewed plugs and leads so can't be them. The coil packs are the only thing left you havn't changed. Hope the new lambda you fitted is Bosch as I was warned that cheapo makes don't necessarily send the correct range of voltages back to the ECU.

Rough running can be caused by indavertant swapping of the two cables to the VVC solenoid. Might be worth checking.

The ECU ascertains how much fuel to inject, based on readings from the engine's sensors (including Lambda) - you might try switch cleaner spray on the multi-plugs from loom to ECU to be sure accurate voltages from the sensors are coming through. In fact, you may as well do the same on all the sensor connections if you can - and the connectors on each injector.

Because you say all electrical things have been checked, so I assume all the sensors have been tested. That leaves fuel and air issues to consider.

Perhaps you have a warped throttle body causing the butterfly inside to jam? Typically caused by overtightening the band that retains the airhose to TB. This get's disturbed when hanging a K&N filter off the TB. It's tempting to overtighten the big jubilee clip.

How clean is the air filter? A clogged filter would encourage a rich mixture which is more of a problem for a warm engine.

I can't think of anything else...

J Lennon

This thread was discussed between 16/05/2011 and 26/05/2011

MG MGF Technical index

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