1991 Subaru Legacy rough idle with misfire on one cylinder.

[olddurro]

All cylinders have good compression. There are no vacuum leaks. New plugs. All new injectors and moving them around makes no difference. Mechanics at Livery Dole (Exeter) are now thinking that it's an electrical wiring issue or ECU fault. The car is older than all the mechanics!

Anyone got any ideas as to how to check the 12v and High Voltage circuits. Can the ECU be tested?

 

[Mark Monte]

It might help to know the actual car you are working on, and the mileage (or kilometers) since the design might make a difference in the diagnosis.
It is always good to start with the basics.
For example, a lot of newer cars are using COP technology.
COP stands for "coil on plug", so even though the spark plug might be good, the coil might be bad.
I once had a problem with a rusty connection at the top of the plug! Dielectric grease works well on high voltage connections.
On an older car, it might be the sparkplug wire itself. Check them for resistance. A good shop might use an oscilloscope to monitor the plugs and identify which one is not firing.