My beloved 1986 Camaro, which I bought brand new has a problem which no one seems able to solve. The car starts fine when it is cold. But if running errands and restarting off and on, it does not want to restart. The starter is fine. There are new sparkplugs and the injector was cleaned. This is the second engine (2.8 liter 6 cylinder, standard transmission), and total mileage is around 350,000. The problem seems to be worse when the gasoline is below half a tank, although the problem is ongoing, even with a full tank.
By “not restart” you mean it cranks and cranks but fire the engine?
I’d think a clog in the vapor recovery system may be at fault. Vapor canister purge valve or the canister itself has broken down. When it won’t start, remove the gas cap and see if it starts. If it does, the tank’s vent system is clogged once it gets hot and not allowing fuel to flow. I’d check the pressure regulator as well. I’d also hook up a pressure gauge to the fuel rail to determine if the car is getting enough (or any) fuel pressure when you are hot cranking it.
Hot start problems often point to electrical problems so I’d check for spark when the car won’t start. If it has spark, it is a fuel problem.
There are lots of things to check and if your mechanic is stumped… I’d be looking for a better mechanic! Be prepared to spend the money for his time diagnosing this.
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On the electrical side of things a bad ignition coil will work fine until it gets hot. That was a common problem back in the day.