Another update. Matt and I spent a few hours this afternoon going through some diagnostic testing on the ECU. Voltages, resistances, duty cycles etc were within spec. The only thing out of spec seems to be the AMM and it's acting like it should, just not quite the voltages we expected. We're not convinced that will cause the issues we're having.
I'm getting a little ahead of my self actually. It would seem it was only running on 2 cylinders last night when I got it running. We got it running again today on two cylinders but... while swapping plug wires around to see if we could get it running on the other two cylinders, we figured out 2 and 3 plug wires were backwards on the distributor.
So it would seem my prognosis about retarded timing and excess fuel was simply a case of unburned fuel entering the exhaust manifold or turbo and burning there. Ian and I swapped the distributor cap Friday afternoon so there is a logical reason why these wires would get mixed up. Anyhow, once we got the right wires running to the right cylinders, it started and ran on all 4 and actually ran fairly well...until it died for no apparent reason. Then it would be difficult to start but when it started it would run fine...until it died again.
Once it was running, we went through the ECU with all the diagnostic tests as above. When nothing raised any flags, we started bringing up reasons why it would lose spark or fuel and die. The only logical reason we could see was bad fuel so we drained the tank and put 15L of fresh premium fuel along with a couple of bottles of gasline antifreeze in case there was water in the system. Didn't seem to help. So now we are scratching our heads again, wondering what would cause random fuel or spark failures. If I hold the throttle open to keep it above 1500 rpm, it'll run all day. Let it drop down to idle and it may run for 5 minutes but it may run for 5 seconds. Most times when it starts to die, it will drop 2 cylinders first, then die. Sometimes we can catch it with some throttle input but most times once it started to die, it would not be otherwise convinced. Unfortunately we don't have any way to watch spark and fuel on all 4 cylinders at the same time so it's difficult to tell what is dropping out. I suspect spark because it will occasionally pop some black smoke out the tail pipe when it is starting to die.
So the big question is...why is it randomly dropping spark. And...when it does, why does it seem to be 2 cylinders at the same time?
Tomorrow I'll pick up a new distributor cap and rotor. We can't see anything wrong with either one but it can't hurt to eliminate yet another suspect.