Ignition Test Not Working

[BryanG]

Ignition test does not fire coils. This test had been working on my Audi A4 with a 1.8T (Coil-on-plugs). I stopped getting spark around the same time a connector broke and shorted two of the wires, causing weak intermittent spark. I replaced the connector (correctly) and nothing. Also worthy of note, at the same time as replacing the connector I ran the fuel pump for around 15 minutes to drain the tank which I know can be connected to the same positive rail.

 

To troubleshoot, I unwrapped the harness a decent amount to check for shorts and everything looked good. I unsoldered the new connector and capped the wires. I checked with a second set of ignition coils and spark plugs. I checked ground, and bridged it just in case.

I'm still getting 12v delivered to the coil packs, and have double checked all the fuses. 

I haven't changed any ecu settings, and spark mode is set to falling edge (I tried rising edge just it case without success). I reinstalled the software, reset the ecu to factory setting, tried the Audi TT base map and anything I could think to do like restarting my computer.

When the test is set to run, I do see battery voltage drop by around 0.5V. The only thing left I could thing of is that the transistor doing the switching inside the ECU is not functioning properly. I'd like to test with an oscilloscope, but it's currently packed up.

Any ideas or advice?

[BryanG]

Update: Never doubt the ECU. What I thought was the fuel pump relay was the engine control relay. Tapping on the engine control relay immediately caused the spark plugs to fire until it lost good contact.

I ruled out the ECU first. I used an oscilloscope connected to the coil signal wire from the ECU. With no coil packs plugged in, the square wave from the ecu was clean. When a coil was plugged in, the trigger wave went flat. Must have been weak contact between the +12v pins, causing the voltage to drop until it couldn't maintain the signal current.