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MG MGF Technical - TF misfire

I have a slight misfire on my 02 TF160 which occurs in fairly specific circumstances, but repeatably.

With he car in (any) gear and being driven forward then back off throttle and lose speed without touching breakes, then accelerate, the car misses. It feels like 1 cylinder misses and, dependent on speed and load(ie up hill), can splutter once or a few times. It then recovers and runs fine. No problem when pulling away in first either.

I have borrowed an OBD reader (thanks Tim J) but no fault codes registered stationary or when misfire forced.

Last service was major one with plugs replaced, and HT leads have been replaced a couple of years ago.

Any ideas?
David M

This definitely sounds like a problem with the spark, although poor fueling can cause a similar problem.

I know that the sparks and leads have been recently replaced, but I'd look at the plugs (are they a normal colour?) and check their gaps. Then look at the lead connections - are they clean and soot free? Then we're looking at the coil packs in the cylinder head. Not sure of a good test for these - hoping that someone can educate us! :o)
Rob Bell

Hi Dave,

I assume the continuous misfire monitoring tests didn't reveal anything then? As I mentioned to you the other day, I had something similar on an old Metro which turned out to be a slight inlet manifold leak. Might be worth checking for, plus all the various hoses.

Alternatively, if you just want to check the plugs and leads by substitution to see if the problem goes away and don't want to spend £££ on new ones I have a perfectly good (used) OEM set of both in the garage you're welcome to try! No spare coils though, I'm afraid. :)

Cheers,
Tim
T Jenner

Thanks for the offer Tim, I cal or email you.

I only succeeded in getting Digimo to work, the other 2 progs wouldn't connect. The misfire monitoring tests either came back with complete or not complete. The latter seemed to be when the interface was going up and down. In either case I didn't seem to get any other data.

Perhaps I'm using it wrong.
David M

I have definitely had the other two progs working - from memory I think they both need the engine to be running, whereas Digimo only needs the ignition on. They also don't seem to like you switching between them - I know one of them would only connect after a reboot after I'd been playing with it for a while. To be honest, though, Digimo's the best by quite a long way; they're only going to be calling functions within MEMS anyway so they're only presenting the same data to you in different ways.

Cheers,
Tim
T Jenner

Hi David
The only test i have used in the passed is to remove the plugs connect the leads as normal then connect all the spark plug bodys together bonded to a earth point on the car.
Turn on put in third gear on a flat road push forward each plug should spark in turn and have the same colour blue spark.

As for the fuel check that the tank is not under a vacuum that is too high for the pump to pull the fuel.
Try a temp fill cap with a breathing hole in it.

Regards Roger
RJ Rowlinson

This thread was discussed between 21/07/2008 and 23/07/2008

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