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MG ZR ZS ZT Technical - MG ZS 180 Mis- Fire

My 2001 reg ZS 180 has developed a mis-fire, my local dealer has exhausted vitually all routes possible in trying to identify the problem, including the use of a donar ECU to prove that my ECU is not at fault. They now suspect the wiring loom, but I think they don't really know. They have used their MG Rover diaganostic kit and this keeps leading them back to number 2 cyl, they have checked plugs, leads, fuel injector, compression test,swapped coils with other cyls and tried well vitually everything.

The fault shows on the dash as a flickering engine warning light but within a few miles the light goes on permanently, the engine lacks power intermitently and then is briefly ok. These symptoms have been getting progressively worse over the last 6 weeks, the car now mis-fires almost all the time during running although tick over it is not so pronounced. Anybody out there know what the cure for this is please.
G J Voller

Have a read of MG enthusiast mate, there is a article on the MG ZS which says:

that the two electric actuators fitted to the VIS (variable Intake system) can fail. Problems here will reveal themselves through a delay or stuttering in the power delivery.

Not sure if this help but its worth a try... what reg is the car?

M R Reynolds

I worked on a ZT V6 the other day that started running rough and got progressivley worse and it turned out to be the Catalyst in the front pipe of the exhaust. Also there is an Earth lead bolted to the cam cover near the bulk head I have known these to be taken off when changing the plugs and not put back on
Martyn

Checked plugs, but have they replaced it/them? I have come upon misfiring on these before that is caused by defvective plugs.

Rog
Roger Parker

Thanks to you all, I shall chase down your observations and see what I come up with.
Further notes:
I had both VIS valves replaced in Jan as they showed themselves up as 'being noisy' at the cars 50K service interval and then subsequently they showed twice on the diagnostics test as being faulty.

Plugs - At the service in Jan they changed all 6 and this is the first time this has been done I believe. Following the service this mis-fire problem started occuring and they eventually traced it to the plug in No 2 Cyl which they re-newed again! I was very surprised the garage believed this plug to be faulty, however it was changed and for a couple of days the car ran OK ish then back came all the problems.


Latest update - I've driven 400 plus miles this last week and for the first 100 the car was a dog. Symptoms expanded into the revs sweeping between 1200rpm - 200rpm all of which at idle or sometimes the car stalled.

For the remaining 300 miles the car was running very strongly, the engine light went out and the mis-fire all but disapeared ! The revs at idle are bang on 800rpm again. I am begining to think there is a ghost in my machine ?
G J Voller

I have a similar missfiring problem with my ZS 120. Every so often the revs shoot up at idle , or as I am driving along / moving away it just completly missfires and it becomes a real struggle. Next day problem wont be there . garage hasn't been able to find anything . Any thoughts ?
Phillt

This thread was discussed between 27/03/2006 and 26/04/2006

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