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MG MGF Technical - misfire only when engine heated up

Can anyone give advice on route to follow on my 1996
MGF 1.8i . the symtoms are as follows :-

Car starts first time and runs smoothly and normally
until the instant the temperature gauge reaches normal
(that is half way ) Immmediately the engine then starts a light misfire which gets heavier under load.
At idle the revs go between 900 and 700. Switch off
and the car refuses to start until the car is stone cold. Have done all the obvious things and replaced
plugs, leads , distributor cap, plug leads , fuel
filter , checked all sensor plugs and even tried swearing at basil fawlty style. Do I need to book it
in at £55/hr to my local rover dealer or does someone
recognise this fault. Please help as I need the car next week to go my holidays.

p.s Mg owner 34 years and delight in getting dirty.
iain mitchell 1

Have heard the coils can fail and need replacing my vvc had new ones at 24,000 miles
D Kimberley

Would agree. Warmed up coil could cause such failure due to inner creaks.
Dieter K.

I was just about to suggest the coils too! Might also be worth renewing the ignition leads as a matter of course.
Rob Bell

Thanks for your replys and I agree a faulty coil could
be to blame ( had a similar problem with my v8 but it stopped in its tracks) but it only fails to start if I
switch it off. However tried again tonight and same again infact you could set your watch by it. cleaned
coil connections and checked leads and plugs the old
fashioned way and all was well with a real healthy spark to all plugs. again it will not restart until tomorrow morning when it will start first time.How about crankshaft sensor,coolant sensor, lambda sensor?
the v8 has none of these is this the moral to the story
iain mitchell 1

"Mg owner 34 years and delight in getting dirty."
Iain, try contacting the CSMGF register http://www.csmgf.co.uk/
they might be able to help with the MG as well;-))




mike

>> How about crankshaft sensor,coolant sensor, lambda sensor? <<

I think that you'd find other problems with any of these Ian. I'd expect you'd get poor general running with a cranksensor fault - but it is a possibility.
Coolant sensor problems usually give rise to a fast idle and non-operation of the radiator fan.
A Lambda sensor fault, I would not have thought, would give a problem with hot starting?

A session with the car connected to Testbook ought to give some insight to these problems, but you'll do no harm by cleaning all the sensor contacts with contact cleaner.

Otherwise, this sounds rather like fuel evapouration... I wonder if your fuel pump is in full health?
Rob Bell

Thanks to Rob and the rest of you for replying to my call for help. However this problem has been going on too long now and I have reluctantly ( after all these years of MG ownership doing my own repairs) booked it in to my rover dealer for testbook tomorrow
and will post the outcome perhaps to save someone else
the grief. For the anoraks out there my car is No44 off
the production line and this is my first problem with it. Thanks again
iain mitchell 1

car fixed on testbook coolant sensor faulty and brain reset to default settings which seemingly should have been done after hgf. they also think i have got "sticky valves "and can repair for £750 + vat.Put
them straight on that count. drove it home and drives like new.
iain mitchell 1

Great news Iain! :o)

BTW - "Sticky Valves"? What is that supposed to mean? ;o)
Rob Bell

>> BTW - "Sticky Valves"? What is that supposed to mean? ;o)

Prune juice might help. ;-)
Paul Nothard

prune juice i'm not very keen on but unofficially my
"rover expert" tells me to try brake fluid directly into my air intake and that will do the trick and if it works try doing the the same with the car.
iain mitchell 1

This thread was discussed between 20/07/2004 and 26/07/2004

MG MGF Technical index

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