Audi A6 + RS6 (1997 - 2004) - N reg Avant 2.0 petrol - Occasional misfire

Honest John Back Room » Technical matters
View Threaded
Tue 20 Nov 2007 16:39
N reg Avant 2.0 petrol - Occasional misfire - wogerthewacer
I have inherited my late father's Audi A6 petrol Avant and whilst it generally runs well and returns 34mpg I have had a nagging problem. It has a misfire sometimes! It is more a hesitation or hiccup rather than a regular miss. The odd thing is that if the engine is switched off and restarted it normally totally dissappears. When I first got it, 10,000 miles ago I replaced the rotor arm, dis cap and plugs but the leads look fine. The fact that it can run clean makes me think it is a sender or of course the ECU. As it is not dire and not changing in its occurance I am reluctant to replace everthing or of course pay a dealer more than the value of the ncar!!. Any help appreciated. Cheers Roger

Edited by Dynamic Dave on 20/11/2007 at 18:30

Reply | Report as offensive | Link
Wed 21 Nov 2007 11:24
N reg Avant 2.0 petrol - Occasional misfire - ggh1
Hard to trace misfires on my 2L AGG engine were caused by a cracked and tracking (single) ignition coil and by perished wiring at the senor end of the crankshalf position sensor.
Reply | Report as offensive | Link
Wed 21 Nov 2007 11:53
N reg Avant 2.0 petrol - Occasional misfire - Armitage Shanks {p}
Any Misfire could damage/pollute the catalytic convertor (if fitted).

Edited by Armitage Shanks {p} on 21/11/2007 at 11:54

Reply | Report as offensive | Link
Thu 29 Nov 2007 15:33
N reg Avant 2.0 petrol - Occasional misfire - wogerthewacer
Hi thanks for you words. Did yours misfie all the time or just now and then? Cheers Roger
Reply | Report as offensive | Link
Wed 26 Mar 2008 15:40
N reg Avant 2.0 petrol - Occasional misfire - wogerthewacer
I now have the answer!! John Bowles VW/Audi specialist in Sevenoaks had the car for three days and changed the thermostat, some improvement, changed the air-control valve, no change so old one put back, the lamda sensor changed, had been running rich, and finally found that the ECU RELAY was at fault. Now perfect
Reply | Report as offensive | Link
Thu 29 Nov 2007 15:31
N reg Avant 2.0 petrol - Occasional misfire - wogerthewacer
Well we have put it on an electronic fault tracer and at first showed a fault with the anti-knock sensor. However when the engine was running it showed no fault. It would wouldn't it! Anyone know where to find the engine ECU. Its not under the rear seat (the ABS ECU is there), the chamber around the wipers or either rear wing.
Just to eliminate any possible theories it has a normal coil pack and distributor with rotor arm.
Reply | Report as offensive | Link
Thu 29 Nov 2007 17:16
N reg Avant 2.0 petrol - Occasional misfire - Screwloose
woger

The ECU is in the N/S footwell. Find the three-letter engine code.

A slight hesitation could be many things. Clearing by cycling the ignition might idicate a faulty key-switch, ign amplifier; a feed relay fault; a VAF sensor fault - or many, many, others.
Reply | Report as offensive | Link

Looking for a garage you can trust? Honest John's Good Garage Guide has thousands of reader recommended garages, plus how-to guides and tips on servicing.

The Good Garage Guide