I've never seen this one before, it's on a 91 Civic Dx automatic. Randomly the car will not start, usually on hot days, usually when the tank is above 1/2-2/3 full. After letting the car sit for any length of time, from 5 minutes to several hours it will not start. The fuel pump runs, so I know the problem is not the main relay. If cranked long enough it throw a code for a primary injector ckt malfunction. Open the gas cap and let it vent, and the car will start. Runs beautifully other than the random no start.

Strangest thing I've ever heard of. I haven't had a chance to check the fuel pressure, it's not my car, so it always happens when I'm not around. I think the issue is with the EVAP system, or more accurately I can't think of anything else that would have to do with the gas tank being vented.

I put this here because the EVAP system is mostly the same on all models.

Any ideas?

 

Possible sticking/ leaking primary fuel injector

 

Have you replaced the gas cap in case the vent is not working?