robertjholt

Hi All,
I'm having trouble with my 97 A8 4.2l.

I getting misfire events from VAG-COM:

16688 - Cylinder 4: Misfire Detected
P0304 - 35-10 - - - Intermittent
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-00 - -
16688 - Cylinder 4: Misfire Detected
P0304 - 35-00 - -
16689 - Cylinder 5: Misfire Detected
P0305 - 35-10 - - - Intermittent

It's doing some strange things...it will start up just fine, idle for about 20 seconds and then just die. I ran a fuel pressure gauge on the line when theis happened and the psi was pretty constant at 55-60lbs, so I don't think this is a fuel pressure issue. I've changed the MAF, all plugs, one coil pack, ICM, Ignition switch, ECU and checked all the vacuum lines. The engine sounds tight and it has a new battery and alternator. In addition, to the above issue, when I drive it, it will shudder under load when it shifts into the higher gears. This shuddering goes away when I back of the gas.

I have some more coil packs on the way to swap out on cyl 4 and 5. In addition, I have a TDC sensor on the way and I will be swapping that out as well.

I wanted to get some insight as to what you guys might think this problem is...

robertjholt

Found the problem...Maf that I replaced was faulty. The misfire is the coil packs. The reason for not realizing that it was the coil packs was the fact that 6 of them were shot. Insane...I haven't had this problem since I was working on wasted spark systems on motorcycles. If you ever want to replicate this issue on your car without having to drive for ever and keep scanning for codes, jam it in reverse, hold your left foot in the brake hard and raise the revs to simulate a good under load test. I did this with the vag-com and could clearly see which cylinders were misfiring. It was only when the car was really hot though. The two that had failed the worse were on cylinder 4 and 8. Surprise - they are both at the back of the engine where it's the hottest. Now on to the transmisson fluid change to lessen the harsh shifts.