I have a multiple misfire and misfire on cylinder 2 and 4

I am starting to get crazy with my local Audi repair shops. Here is what happened.

First problem: the car doesn't start.
the garage change a lot of things to fix compression and cam timing off. The car runs well for about a month.
Then I got a misfire on 1 and 6. He recalibrated the timing. Car runs Ok for about 2 weeks
Again multiple misfire and on 2 and 4: replaced the coil pack. Runs well for about 3 days.
Again multiple misfires and on 2 and 4. Replaced the gas filter. this time got serious doubts this would change anything. But the car runs well for 2 days
Again multiple misfires on 2 and 4. Went to another place and the guy says it is the thermostat because the car runs with too low temperature. Now I have very serious doubts. I cannot see any relations between the misfires and the thermostat.

Independently of what they say, after the car came out of the garage previously, I went well with a very smooth idel for one or 2 days and suddently gets the misfires.

One of these times, I was doing bad misfires in the parking lot (blinking check engine). It Went to the garage on the platform. Arrived at the garage it was running smooth. The only difference I see is that the car went on and off the platform and got inclined.

Any idea what to check? I am now completely clueless and it seems that I cannot trust the guys who tried to fix the misfire.


many thanks in advance for your help.

 

did you check the plugs and replace the wires. i had misfires on 1 and 5 replaced wires and plugs no issues after 5 mths so far

 

Yes They were changed recently. I doubled checked with probe to be sure there is fire on the terminals and yes it there is. The spark plug are new. However, still get misfire on 2 and 4. I start to suspect the wire between the ACM and the ignition coil. I found this procedure to be followed according to an Audi tech note:

http://ww2.justanswer.com/uploads/Hi..._ACE_-_101.pdf

I will keep you updated on what I discovered.

Cheers
Didier

 

OK, we found the problem with a friend's lab scope. It is incredible how useful this tool is!

a) we probed the Coil pack input and noticed that the signal was OK.
b) Resistance on coil 2 and 4 (it is two sides of the same coil on 1999 Audi a6 2.8) was OK
c) the spark plug were very dark due to all the misfire we got on 2 and 6.
d) during a misfire episode we were able to test the coil output on 2 and 4. Surprisingly, 4 was OK and 2 got nothing. Since the event was intermitent we had trouble to observe the problem in action. Having a single spark on a dual coil indicated some problems in the ouput.
e) we also noticed that the coolant temperature was very low. We are located in Quebec and the winters are very cold here. At -20C the temperature never reached above 60C.

Action:
a) Changed the thermostat. The one changed by the garage was a volskwagen thermostat but a wrong one. The set temperature was too low and this leads to too much carbon deposits. I noticed a tech note from Audi mentionning that a new hotter thermostat should be installed. That thermostat has the same parts number but ends with a G instead of a F. The new improved thermostat is set to 92C (part No 078 121 113 G) . I recommend to use the OEM thermostat, otherwise you may end up with the wrong temperature and carbon build-up.
b) Changed the spark plugs for the recommanded ones by Audi. Got them from ebay for half the price Audi sell them. NGK BKR6EQUPA.
c) changed the coil pack for a new one ( a bremi). I have to get a good and viril talk to the garage owner where the last one was changed. He installed a real crap.
d) did an oil flush
e) changed the oil and filter

The car runs well now. Maybe a little instability on idel. Most likely a durty trottle valve. Need to be cleaned.

The tech note from which I got the clues is: 150102

cheers
Didier