Demon Missfire

[J-J]

Just bought a 172 cup and its developed a hell of a missfire.

It idles fine for about 30 seconds then miss fires as though its about to stall, it does the same when driving, when it hits about 3000 revs it starts missing and looses all power, then after some different pedal combinations will pick up again. I have managed to drive it though without it missing at all.

Any ideas what's causing it and how to fix it? I've been told it needs a new front Lambda sensor, also going to change the temp sensor and Engine control relay's. Does any of this seem OTT or is there anything else I could change?

 

[Mark One]

lambda won't hurt. Normally improves MPG a lot

as for your missfire, it's almost certinally a coil pack. These go so often on french cars that an AA man may even have on in his van. So if your a member, that could be cheap.

 

[r516vt]

Have you checked the plugs?

 

[J-J]

lambda won't hurt. Normally improves MPG a lot

as for your missfire, it's almost certinally a coil pack. These go so often on french cars that an AA man may even have on in his van. So if your a member, that could be cheap.

Its just has a new coil pack fitted and new plugs so can't see it being them.

 

[Jonff]

Suppose it could be anything ignition wise, i.e ht leads, sparkplugs etc.

 

[Mark One]

Its just has a new coil pack fitted and new plugs so can't see it being them.

fun then!
Going to need to start trouble shooting. But personally. I still wouldnt rule out a dodgy coilpack. If you've got a mate locally who can lend you one of his 1*2 could be worth a try.

Consider giving the throttle body and good clean too with some carb cleaner. If it's fubared that will ruin your idle.

 

[OldClio172]

You also need to check the wiring loom, they are common for rotting, my friend at work had this happen on his and it caused a lot of issues sounding similar to yours.

He got the wiring sorted and the control relays as you mention and it was fine.

The Lambda sensor is a good starting point though. he tried all the above too, cleaning throttle body as he thought that was it but it was fine, tried coilpack, plugs, leads and all didn't work.

In the end sorting the wiring under the fuse box and replacing the relays did the trick.

Electical gremlins are time consuming but hey, its a renault !!!

Apparantly its common for the loom to rot under the fuse box and this sounds very similar to his problems too.

See how you go and if you get no joy I will speak to him and see if he can help.

 

[Mark One]

not sure about looms rotting on a car thats about 7 years old and well looked after.....
more a mk1 thing that, and even then, ive never seen it. possibly check the earth strap though

 

[OldClio172]

Happens a lot, the local specialist I use said he's seen a good few, its just where the wires are exposed under the fusebox apparantly.....

They get oxodised to death.