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Will

MOT failure - missfire

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My VR's just failed its MOT on the emissions and they also pointed out a missfire, which I was already aware of.

 

Anyway, it turned out the missfire was down to a broken plastic ignition lead insulator on the coilpack - it was arcing between the lead and the metal body of the coilpack.

 

My question is, if the engine is missfiring, does the car automatically run in 'limp mode', or whatever it's called. I've quite often had 'intermittent signal - lamda probe' thrown up on VAG-COM and have even changed it but it didn't solve the problem. I was thinking that maybe the ECU senses a missfire and sets the car to run rich automatically - does anyone know if that's the case?

 

Obviously the emissions should be improved now as the fuel in the offending cylinder is now being properly burnt, but it was quite over the maximum levels out and I only get one free retest!!

 

Thanks in advance.

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The ECU does not pick up any missfire's fuel is still being injected into the cylinders at all times,if the spark stops due to misfire it still injects fuel and then you will have unburnt fuel being pumped out the exhaust which will be quite high on the emissions.

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