Need some help from a good troubleshooter to diagnose misfire problem (long)
11-29-2006, 05:19 AM
#1
AudiWorld Super User
Thread Starter
Need some help from a good troubleshooter to diagnose misfire problem (long)
OK, I recently bought a 3.0 after my B5 was totaled by some idiot who ran a light. Well, I got the B6 pretty cheap (12k) but it had 118k miles on it. The car is cleal inside and out with all scheduled maint done (yes TB was done) and runs and drives smooth but I got a CEL with theses codes:
16684 Random/Multiple Cylinder Misfire Detected
16685 Cyl.1 Misfire Detected
16686 Cyl.2 Misfire Detected
16687 Cyl.3 Misfire Detected
16688 Cyl.4 Misfire Detected
16690 Cyl.6 Misfire Detected
19989 Cyl.5 Misfire Detected
So it's random on all cylinders when it's idling. The only way I knew this was happening was because of the CEL and connecting to the VAG to look at blocks 14 15 & 16. Also, I did notice that the idle felt a little rough after siting at a light for about 30-60 seconds but I thought it was normal.
Since then here's what I've done to trouble shoot:
1) Changed all plugs with OEM NGK's
2) Changed all coil packs to latest updated version
3) Fixed a broken vac line to the FPR
4) Test intake pressure and FPR (normal)
5) Tried different gas
The only thing that stopped the rapid misfires was switching from 93 octane to 89 midgrade octane. For comparison, when 93 was in there, I would get up to as many as 40-50 misfires in block 14 (total for all cylinders) before it reset to zero. When I switched to 89 just for kicks (read a post where the dealer told someone the octane was too high) and came right home to put it on the vag. The misfires were reduced to like 1 or 2 before reseting to zero. So I was thinking that this was fixed but it seems that the ECU is just compensating for the lower octane.
That was great but with the lower octane, you notice a performance loss. I'm thinking that if the car was designed for 91+ octane, it should use 91+ octane with no problems. If this will not have long term problems I'd be OK with it, but I'm not sure. I don't want the lower octane to be masking another problem. I'm the only one on the B6 forum with a 3.0 that's having this problem. Everyone else uses 91 92 93 octane with no probs.
All that being said, do you think it's an ECU issue? Is this something that can be adapted in the ECU to fix? I'm all out of physical culprets to look for because the car is running fine. If it was the fuel system, I would have probs starting, smelling fuel, or drivabilty probs but I have none. I've checked for vac leaks and even the shop I took it to couldn't find anything. They said the car looks perfect and they were the ones that suggested that it could be an ECU problem. I found the 89 octane fix after I took it to the shop. I was thinking that they were just throwing out a suggetion because they didn't know what it was but after the 89 fuel, it seems that the car is just not burning high octane fuel effectively. So the ECU suggestion is not looking to remote of an idea.
Any suggestions would be greatly appreciated. I've been posting on the B6 forum for a couple of weeks now but that forum hasn't got the research behind it like the B5 forum does.
16684 Random/Multiple Cylinder Misfire Detected
16685 Cyl.1 Misfire Detected
16686 Cyl.2 Misfire Detected
16687 Cyl.3 Misfire Detected
16688 Cyl.4 Misfire Detected
16690 Cyl.6 Misfire Detected
19989 Cyl.5 Misfire Detected
So it's random on all cylinders when it's idling. The only way I knew this was happening was because of the CEL and connecting to the VAG to look at blocks 14 15 & 16. Also, I did notice that the idle felt a little rough after siting at a light for about 30-60 seconds but I thought it was normal.
Since then here's what I've done to trouble shoot:
1) Changed all plugs with OEM NGK's
2) Changed all coil packs to latest updated version
3) Fixed a broken vac line to the FPR
4) Test intake pressure and FPR (normal)
5) Tried different gas
The only thing that stopped the rapid misfires was switching from 93 octane to 89 midgrade octane. For comparison, when 93 was in there, I would get up to as many as 40-50 misfires in block 14 (total for all cylinders) before it reset to zero. When I switched to 89 just for kicks (read a post where the dealer told someone the octane was too high) and came right home to put it on the vag. The misfires were reduced to like 1 or 2 before reseting to zero. So I was thinking that this was fixed but it seems that the ECU is just compensating for the lower octane.
That was great but with the lower octane, you notice a performance loss. I'm thinking that if the car was designed for 91+ octane, it should use 91+ octane with no problems. If this will not have long term problems I'd be OK with it, but I'm not sure. I don't want the lower octane to be masking another problem. I'm the only one on the B6 forum with a 3.0 that's having this problem. Everyone else uses 91 92 93 octane with no probs.
All that being said, do you think it's an ECU issue? Is this something that can be adapted in the ECU to fix? I'm all out of physical culprets to look for because the car is running fine. If it was the fuel system, I would have probs starting, smelling fuel, or drivabilty probs but I have none. I've checked for vac leaks and even the shop I took it to couldn't find anything. They said the car looks perfect and they were the ones that suggested that it could be an ECU problem. I found the 89 octane fix after I took it to the shop. I was thinking that they were just throwing out a suggetion because they didn't know what it was but after the 89 fuel, it seems that the car is just not burning high octane fuel effectively. So the ECU suggestion is not looking to remote of an idea.
Any suggestions would be greatly appreciated. I've been posting on the B6 forum for a couple of weeks now but that forum hasn't got the research behind it like the B5 forum does.
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11-29-2006, 06:02 AM
#9
Keeper of the Cash
Fuel injectors, ignition coil, and spark plugs are the only major components the repair manual
lists for the code. You can use output tests to check their function, but I would def look into those.
11-29-2006, 06:04 AM
#10
Guest
Posts: n/a
Holy fvcking lack of reading comprehension:)
Seriously, replace the fuel filter and try a can of Techron.
Higher octane burns slower. Carbon buildup soaks up some of the fuel, so you end up with a lean, slow burning mixture. The end result is misfires at slower piston speeds.
I would also consider running a Toulene mix for one tank.
Higher octane burns slower. Carbon buildup soaks up some of the fuel, so you end up with a lean, slow burning mixture. The end result is misfires at slower piston speeds.
I would also consider running a Toulene mix for one tank.