schaeffer

Hi,

My wife's 2004 A6 has the multiple misfire problem.

Saturday,12,February,2011,16:05:46:41012
VCDS Release 10.6.3: Generic OBD2
Mode 03: Emission related fault codes

Address 10 (Engine): 4 Faults Found:
P0300 - Random/Multiple Cylinder Misfire Detected
P0304 - Cylinder 4: Misfire Detected
P0303 - Cylinder 3: Misfire Detected
P0306 - Cylinder 6: Misfire Detected

After searching this forum and the web for the location(s) of the ICMs/power output stage and looking at my car, the information I've found doesn't seem apply about being mounted on the air cleaner, the firewall or next to the w/w reservoir.

I want to try diagnosis by component switching as is mentioned frequently.

The Bentley A6 Service Manual I bought has a misprint and I found that the picture in the Fuel Injection section, page 24-14 which lists components is not for components 1-16, it's a duplicate of the figure for components 17-31... I also am not able to find that figure so far in any other sections... pretty frustrating.

Thanks,
Schaeffer

4Driver4

Pull the valve covers and check the condition of the cams.

SloopJohnB@mac.com

My Bentley says 30V AVK 3.0 V6 has separate ignition coils/ICMs for each plug.

Soooo...exchange a misfiring cylinder coil with a coil from a cylinder that is not misfiring and see if the misfire moves with the misfiring coil. If it does, replace the coil.

This is a shortcut...technically you're supposed to move the sparkplug from the misfiring cylinder to a cylinder that is not misfiring and if the misfire moves, replace the plug(s).

If your plugs have 30K on them you're supposed to replace them anyway.

SloopJohnB@mac.com

Note: The ICM/ignition coil is one assembly. You should have six of them, each one sitting on top of its sparkplug.

SloopJohnB@mac.com

Here's an interesting tool I saw used on MotorWeek:


http://www.mpt.org/motorweek/goss/3022.shtml

schaeffer

Thanks for the information, including using a sparkplug tester to test the coils. Now I know why I couldn't find the ICMs.

Since the failure was sudden, the possibility of 3 coils going bad at once seemed unlikely and that's why I started looking for components common to multiple cylinders.

Schaeffer

SloopJohnB@mac.com

Well, audi DID have some problems with coils so I guess it's possible to have three coils go intermittently bad.
OTOH, it's far more likely to have an induction system vacuum leak, so I'd check all the iddybiddy hoses and tubes and sleeves and clamps that go to the intake system.
Generally you'll get a misfire with a lean charge that can be caused by unmetered air (vacuum leak) or too little fuel (low fuel pressure, i.e., failing fuel pump, or clogged injector). But a lean condition should also throw a code unless perhaps the 02 sensor is able to compensate for the lean condition but then you still have the random misfire that the ECU is picking up and throwing a code.

One thing...a code gets set after a certain number of misfires so if you clear the code you might not get an instant code re-hit. A vag-com can track the misfires live, I understand, even if the code isn't set yet. This might help you determine which cylinder is doing it first for coil-switching purposes but I'd still look very carefully for old cracked hoses/tubing or things like emission valves or other vacuum control components that could have a cracked nipple or somesuch.

schaeffer

Good idea. I'm going to check the coils first, then look for vacuum leaks. And if I don't find the answer, will move on to a compression test to get
the basics out of the way and then fuel I guess.

Schaeffer

DempseyKelly

For some reason on my 2005 A4 1.8T, 2002 MK4 Jetta, and my 07 A8, when a misfire happens it seems to always be in multiple cylinders and had usually been just the COP that is to blame.