Join Date: Jun 2016
Location: Santa Barbara, CA
I just re-read your post. It is certainly possible that you have a vapor-lock issue when the engine is hot; an ignition issue is usually go or no go. You would need to connect a fuel pressure gauge to verify this. If the fuel pressure drops to zero quickly after engine shutoff, you have an issue with either the fuel pressure regulator, fuel pump check valve, or possibly fuel injectors/cold start injector leaking down. A huge cloud of fuel smoke out of the tailpipe after the engine does start would be a good indicator of leaking injectors.
As for ignition system testing:
If you have a good multimeter such as a Fluke and set it to read AC voltage, you might be able to get a flash of a signal at the distributor reluctor with the plug disconnected, then see if you get a similar thing to happen at the ignition control module. Not a super accurate test, but worth a try. A good test light will be able to catch the digital switching signal output from the ignition module to the coil negative terminal; again not as good as a scope, but no flashing equals nobody home.
A good digital timing light is also a good quick check of the secondary ignition circuit---clip the clamp around the coil secondary wire when you have a crank/no start condition, while the test light is also hooked up. Then you can isolate whether it is a problem with the primary ignition circuit, coil, or secondary ignition circuit. The original Bosch coils are incredibly durable, as are the ignition control modules, but either could overheat and drop out. Many cheaper modern replacement ignition coils (including the Brazilian-made Bosch ones) are complete junk and always a suspect in these conditions . . .
Chris A: '81 GTV6 rescued from junkyard, "GT" car/'86 Porsche 944 Turbo track/street car/'73 BMW 2002tii fun street car/'74 Jensen Healey Lemons Rally car!