Our 1981 air-cooled 1.9L fuel injected Vanagon had been running fine for the past two years since the engine was rebuilt. We have probably put 2000 miles on it since then. Just recently it has started to misfire.
Traced the misfire to cylinder number 2?.when I remove the wire to that spark plug she actually idled farily smoothly on the three remaining cylinders. First I tried the obvious by swapping spark plug wires, distributor cap, and coil (we have extras) with no change in the symptoms. Next pulled out the plugs and saw that they were all very sooty?with the one from #2 a little more so than the others. Not at all oily, just black carbony soot. While I had the plugs out I checked the compression in cylinder 2 and it was at around 125 psi and holding strong. Whew, looks like valves and rings should be okay.
Put new plugs in and she ran smoothly again?.let it run for about ten minutes with no change. Turned it off, went inside to get cleaned up to take her out for a test spin. Started it back up?..misfire again. Pulled the plugs out and they are all sooty again.
She's obviously running rich? What would the next logicial course of action be? Check timing? Make sure all resistance measurements from ECU are within spec? Grounds are clean.
Thanks!