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MG MGF Technical - Still not right

My 1999 VVC was a little less than sparkling to drive, so replaced plugs and correctly gapped, also replaced HT leads(scars to prove).
Car starts first time and is really responsive, but I have a lumpy idle and there is a very slight misfire at about 1800 at light throttle in traffic.
I have double checked plug gaps and have not dislodged any pipes or fittings. Took the opportunity to remove connectors for engine bay and radiator fans and cleaned as per this board at the same time.
Any suggestions please as the condition mars the otherwise brilliant drive of the car.

Tony
Tony Harrison


My guesses... (and a bump up the thread list!)
o idle vale needing reset
o temp sensor misreading/broken

A trip to a testbook could check sensors... or you could use the usual Haines checks for things like temp sensor...

Let us know what you find.

P.
Paul Nothard

Could be the oxygen sensor as well (IMO)
Is it different whith cold or warm engine ?
Dieter K.

Stop Press !!
Just seen it's a VVC.

I woun't make panic, but might be possible the damn cam wheel bolt is getting loose.

Anyone ?
Dieter K.

Thanks Gents
This has only happened after plug and lead replacemant.
Could it be a faulty plug or are the gaps at 40thou incorrect?
Tony
Tony Harrison

I've heard of a couple of cases recently where the fuel line pressure has been inadequate - but I would expect top-end performance to be affected too, if this were the case.

Cleaning the contacts of the ECU temperature sensor costs pennies, and worth doing irrespective. But it may help if the engine is unable to run on anything other than the 'cold engine map'
Rob Bell

Cr starts and drives fine perfoming faultlessly up to the red line. Really sharp and responsive.
Byt light throttle in traffic say 1800 rpm in third, there is a 'fluffing' sort of mis fire and the idle although stable at 850 rpm is lumpy.
Sensors?????
Please explain where I will find the ECU temp sensor.

Thank you all in advance.

Tony
Tony Harrison

Tony,

I know that this is not an answer that sits easily with your circumstances i.e. the problem only occurred after lead and plug changes, but your description of the lumpy idling and low end power leads me to offer my own experience of similar symptoms in the hope that it may help.

For me the problem simply occurred after some serious use of the rev range at North Weald Airfield on a 1stLotus fun day. The result was lumpy idling - a rythmic sound that resonated in the exhaust and that someone described as sounding just like a Lotus Elise 160 Sports! At low revs the power was lacking, but at higher revs the engine pulled normally right up to the red line.

The problem turned out to be the VVC control mechanism. There are two solenoids and they can stick. Apparently this can be due to dirt or failure.

Now, perhaps as you were testing out your car's performance, after your new plugs and leads, you also suffered this problem whilst at high revs.

Alternatively, perhaps there is a sensor that can provide some sort of reading that would cause the VVC mechanism to be fooled into staying in this mode.

All speculation, from someone who is far from technical, but is at least used to problem solving! I hope it helps.

Dave
Dave

Good thoughts there Dave :o)

Tony, the ECU temperature sensor is located on the head coolant outlet pipe (front right corner) - but from your desciption, it actually does not sound anything like a problem with this sensor.

The rough idle could be due to the idle air control valve (IACV) - which is the system that the engine management uses to maintain a steady idle. You could try re-setting the stepper motor, and perform checks on the IACV pipe work to ensure there is no leakage (WD40 is ideal for this purpose).

But the IACV would not explain the poor running at part throttle.

It may be worth checking the VVC solenoids as Dave suggests - perhaps one or other - or their connections - has become 'gummed up'?
Rob Bell

Thank you guys
Will be on the case tomorrow and will advise outcome.
Very many thanks to all for guidance and help.
Bloody brilliant car anyway.


Tony
Tony Harrison

<<Could it be a faulty plug or are the gaps at 40thou incorrect?>>

Try setting the gaps at 32thou. The data for my 96 VVC shows the gaps at 0.9mm+/- .1mm

HTH

Bruce
Bruce Caldwell

To expand a little more on Daves comment

I seem to remember that Dave got stung for a whole new VVC Mech (or at least something expensive) by a main dealer, subsequently Dave found out that a bit of specialised cleaning would have been sufficient.

It may well be worth visiting one of the MGF specialists. It's too easy for a garage to replace a whole unit and then just charge it on to the punter.
tim woolcott

Thank you everyone who has helped with this thread.
Problem gone but not sure what I've done.
Spark plugs regapped to 35thou, all sensors I could find where cleaned and refitted.
Finally, left car running for 10 minutes after a fast run and all three fans cut in and out again as they should.
Regular checks will be made of the radiator fans to ensure they always work.
My wife has been instructed to treat the water temp guage as the most important instrument in the car.
Thank you all and enjoy the fine weather motoring.

Tony
Tony Harrison

This thread was discussed between 07/07/2003 and 12/07/2003

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