Heavy Misfire at Idle

[Belle427]

I made a schoolboy error when connecting up my Vauxhall electric power steering pump control wire, I connected it to coil negative instead of positive.
There is very little load on it as it’s used to signal the pump to run.
I’ve left it disconnected for now to eliminate it from the problem.
Car starts and runs but has what seems a multi cylinder misfire now and again, it almost stalls but recovers. Rev counter drops to zero when it happens.
I replaced the ignition module as I assumed I’d fried it but no change, tried a spare coil and again no change.
I’m just trying to narrow down what I may have done as problems like this are notoriously hard to pin down.
I’m happy that leads, cap and rotor etc are all ok, the car was fine before this mishap.
I know aftermarket modules are hit and miss but I did go for one from powerspark ignition instead of the dodgy Lucas branded ones.
Any ideas are much appreciated.

[Loubaruch]

I have no wish to alarm you but you could have damaged the ECU.

Probably worth plugging in a known good one if anyone near you has a spare.

No doubt someone like" Blitz racing" on this Forum would be able to confirm if that is a likely scenario

Best of luck

[STE VR]

I shorted something many moons ago and had a hell of a job finding the problem. Turned out it was the afm. Disconnect it and see what happens. Won’t run perfect but shouldn’t misfire. Worth a quick try to eliminate.

[Belle427]

Thanks both, i think ive decided to go for modern management a little sooner than anticipated but i think its the right move.
Bloody cars!

[blitzracing]

The powerspark units are not that robust- I had one fail after less than 5000 miles from new and left me stranded. If the rev counter drops suddenly to zero you are either loosing 12v to the coil, the trigger from the amp, or the trigger from the distributor. Its unlikely you have damaged the dizzy pick up or coil. If you disconnect the king lead and crank the engine you should be able to get a spark to jump about 1cm from the end of the lead to ground that will show if the HT and switching is healthy. ECU damage would seem unlikely as its protected with a resistor against the 150v pulses the coil produces in its primary as the coil discharges, so I cant see how you would exceed this.

Edited by blitzracing on Friday 31st May 18:45

[Belle427]

Thanks.