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MG MGF Technical - Momentary misfire

I don't suppose this is a new one, just not a current topic - I was coming home at about my usual rate along the A70 towards Carnwath (the resurfacing has made a useful improvement), and had overtaken the few cars I had caught up with. This had taken about 6000-6500 rpm in 3rd to make sure, and with the last one I'd had to wait till after my favourite right-hander, when a little bit further on I had a momentary total loss of power. It only lasted about half a second, but I thought I could detect a bit of a misfire therafter for a mile or two. After going through Lanark there was no further sign, and I've not been out in it since. I'm on original spark plugs after 29500 miles, and it's a 96N model. Any thoughts or previous experience anyone, or should I just get the plugs changed at its service in a couple of weeks?
Michael Cunningham

Total loss of power would not occur on all 4 plugs at one time, it would have to be something more central to the system. If the car is a 1.8i then a rotor arm comes to mind from experience. Then there are know issues with the dizzy cap to a lesser extent. Finally the main coil to cap HT lead. All three things will usually have a total effect not just individual cylinders.

If the car is a VVC then you have twin coils with twin direct feed HT leads to throw that scenario out of the window! Nothing else comes to mind at the moment, but if it does then I will add it.

Roger Parker

Was the fuel tank near empty ? ( It could have been some dirt from the bottom of the tank ) It may explain the problem going away after a coulpe of miles

Matthew Minion

If one plug momentarily dies it feels like a subtle shiver, and a very very slight loss of power. If it stays dead, the car will shiver in idle mode, make a deeper sound and will lack noticeably power after 3000rpm. If it really misfires you might think a fat punker is driving behind you with a noisy Harley Davidson ;-) During these 'exploding noises' the car will really stutter and even refuse to accelerate. And if you have an ICON superchip, it will happen all the time :

I know all this because I all had it :-(

Could be a faulty signal from the crank sensor - making the MEMS think that you're over the rev limiter and therefore cutting the sparks for a cycle or two??

N837 OGF

Dirk said....
> If one plug momentarily dies it feels like a
> subtle shiver, and a very very slight loss of
> power.

My VVC does this fairly predictably almost every time I accelerate through about 3.7k to 3.8k revs gently, but not if I accelerate through there fairly hard.

> And if you have an ICON superchip, it will
> happen all the time :

I do have an ICON "race superchip". I've been wondering whether it's a chip problem for months now but haven't found the time to try disconnecting the chip to see if the problem goes away. I *think* it went away for a short period when I used super-unleaded rather than ordinary unleaded.

If it is the chip, then could it maybe be fixed by remapping the chip?

In case it's relevant, I have a Pipercross cone air filter, anti-cat, and MotoBuild 4 pipe exhaust. And, having read the other thread where some people give the 4 pipe exhaust a bit of a bashing <grin>, I do realise it's only a 2 pipe behind the finishers but I like the look and the sound.

I'd be interested to hear what you thought of the chip Dirk. I've had mine for several months now and *think* it improved low-end torque quite a bit but that could have been the dent in my wallet helping me imagine the difference. :)



if you have an Icon chip, I recommend you to always use super unleaded instead of ordinary unleaded. The chip alters the ignition timing (more advance), so it's better to have a higher octane fuel that won't explode too early.


BTW, I remember Dirk had troubles @ about 3800 rpm with his Icon chip

Hey Mark, I had EXACTLY the same, 3750rpm, often, not always. And even the (silver, not blue) MK2 chip did not solve the issue. Disconnecting the chip made this glitch disappear. SP told me a lot of stuff, send me several chips but it always came back, this dreaded 3750rpm, I think ICON doesn't know it either. And when SP offered me a refund they went bankrupt 2 days later, so I got basically screwed.

Finally I think this contributed to 1) busting of 2 sparking plugs from same cylinder, 2) the breakup of the piston of again the same cylinder
Everytime this misfire occured seemingly this piston got a good punch. You can see the result on my webpage in detail.

Do yourself a favour, don't use it

Probably silly but... isn't it the electronic rev limiter?

In that case, that's something absolutely normal.
I already went up to 6500rpm and if you continue to accelerate, the electronics cut the power automatically to avoid the engine to go over the max rpm.

Thanks Dirk, sounds like we have the same problem.

I just spoke to Motobuild (UK dealer down near Heathrow that supplied and fitted the chip) and explained things to them. We agreed that I'd try disconnecting the chip to see if the problem went away, and if so then I'd send the chip back to them so that they could take a look and either send out a replacement for me to try or reprogram that one.

I realise this is duplicating the efforts that you've already gone through Dirk, but I guess I need to do the same before I can either find a fix or get a refund.

The chap at Motobuild has been helpful so far, but this is just the beginning so we'll see. :)



p.s. Is it my imagination or has everyone put their MGF away for the winter? I used to see loads around here on my daily drive to and from work (Burwell near Newmarket to Cambridge Science Park and back) but hardly see any now and they invariably "have the lid up". :(

This thread was discussed between 30/09/2000 and 09/10/2000

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