Hi, my 98 A4 1.8t has a bad misfire. The check engine light is blinking and when i pulled the code its says cylinder 3 and 4 misfireing. I have replaced all 4 spark plags and all coil packs but nothing changed. I olso switched the fuel injectors around to see if the misfire would follow but nothing. Next i checked the power on the fuel injectors and the are all getting power. Next I did the same with the coil packs. I disocnected the wireing harness from the coil packs and check the power and the are all getting about battery voltage. Next I did a test on the Ignition control Unit and measured the resistance and I got the same values on all four pins (about 300k) which seems to be right. This is where I stopped. I don't know what to do next if anyone has any ideas it would be appriciated. This is a tough one.

Summary of what I did so far:
replaced all 4 spark plugs
replaced all 4 coil packs
switched the fuel injectors around
checked the wireing harness on injectors and coil packs
tested the ICU

I guess the next thing I should do is to check the cylinder compression. Does anyone know whats going on here.

 

Sounds like you got a tank of very bad gas. Nobody knows where you live, so we can't make extrapolations due to climate, but I'll bet that is your culprit. If this happened over several tanks, maybe you have another issue.