We have had a problem with our 81 air-cooled Vanagon where the spark plugs get fouled (turn sooty black-not oily) and the engine starts mis-firing. If you clean up the plugs the engine starts and runs fine for about 5 minutes, then you will heat a faint tick which gets louder as the engine gets warmer. If you pull the plugs at this point they will be sooty black again (cylinder 2 & 4 more so than 1 &3 for whatever that is worth.)
So far I have replaced the cylinder head temp sensor, oxygen sensor, fuel filter, rotor cap and wires, as well as the injectors.
I have checked and found to be okay or within spec: intake airflow and ambient air sensors;
-Cold start valve
-Thermo time switch
-Coil
-Rotor
-All of the Hall effect gadgets
The fuel pressure is a little on the high side (31 psi). Is that still within the acceptable range? I checked the return fuel line and it appears okay and swapped out pressure regulators but have maintained the 31 psi reading.
I'm running out of ideas on items to check. Does anybody have any further ideas or insights?