In case anyone else ends up with the same problem, I thought I would post about my recent misfire problem. I have a 1998 A4 1.8T Quattro and a few weeks ago I was driving not far from my house and my check engine light started blinking at me (bad) as well as a loss of power. I limped the car home, pulled the spark plugs, which looked good, and called my friend to bring his computer over. Sure enough, misfire on cylinder 2. We swapped the ignition coils, spark plugs, and fuel injectors and the misfire still happened on cylinder 2. I took a look in my Bentley book and built the LED voltage tester pictured at the start of the wiring diagrams section (it cost about $1.20 to make). Last night I tested wire terminals 1,2,4,5 of the wires running from the engine computer to the Power Output Stage (a.k.a. ignition amplifier, Bosch Ignition Module depending on who you ask). Those all checked out ok. Then I connected my LED tester from Battery Positive to each of the 4 pins that run to the ignition coils and cranked the engine over each time (after disconnecting power to the injectors). Sure enough, the pin for cylinder two failed to cause the LED to blink. I ordered a new one last night for $218. Sure beats paying the dealer $500+ to fix the problem plus the 4 to 5 week wait to even get an appointment with them. I think I spent a total of two hours of my time diagnosing this. I hope this helps someone else.

 

Gotta be AT LEAST one post a week about an ignition amplifier failing. Nice description of the testing of the amplifier itself.

Andy