I have been getting a very bad random missfire on my S8. It will go weeks with nothing and then it starts to miss when starting up or just driving. I have had the plugs changed as they were coming up due anyway, I have put on two new ignition control modules after the first one (fitted by my local Audi independent specialist did not seem to make any difference) It went well for some time then started missing again. On VAG Com it comes up as a random multiple missfire on various cylinders on both banks but not necessarily all of them at the same time. I am beginning to suspect a broken wire somewhere but where to start looking????
Have any of you fine people any thoughts on this? I dont want to use the independent again they were expensive enough and did not sort it. The local Audi dealer wants £115 an hour, something like this I just dont trust them not to wind it out, if it takes a day thats a grand nearly
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This could well be a problem in the 'Final output stage' N122 mounted on each bank. Before you do anything run the engine on a dark night and lift the bonnet and look around for either arching or corona around N122, N192 ( injector amplifier ) and the coils. I have seen random discharge from the 'Final output stage' N122 between casing and the mounting bracket. email me and I'll sent you some diagrams and pointers. Please supply the engine code form the ID label either in the service book or on the ID label in the spare wheel bay. Regards Peter
Edited by Peter D on 28/03/2009 at 09:52
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Peter D
Many thanks for your fast reply on this one; but both N122 and N192 have been changed, I have called these the ignition control modules, the ErWin manual calls them the "Power output stages for ignition coils". The engine code is the AHC 32 valve engine.
Part of my problem is a lack of time to go through the ErWin manual and find the right sections for the faults I get on VagCom.
Do you have any other ideas at all?
Thanks
Daedalus
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Is this a 'mild' misfire. I ask this because there is a Hall Effect sensor (G40) at the back of the left bank which controls the correct timing of the system. However the system is fault tolerant and if the sensor fails the engine reverts to injecting fuel only a closed valve and can make the car shudder due to inconsistant fueling. Inspect the connecor, the sensor and the cabling for and damage. Regards Peter
Edited by Peter D on 28/03/2009 at 14:29
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Further, worth checking the speed sensor although I do not see how that would cause a misfire and reseat the Motronic Engine ECU connector. Regards Peter
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You need to post this on www.vwaudiforum.co.uk Regards Peter
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Peter
Many thanks again for this, I will copy original post to the Audi forum. Forgot to mention the car has done 175,000 miles and has run happily for the last 55,000 on LPG but it misses on both.
Daedalus
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You can often get P0300 codes for reasons other than ignition faults.It is quite possible that your problem is a failing MAF sensor,which is not unknown on this model.If you renew this,I'd suggest only use a genuine VAG part.
David Davies
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