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The truck will start and run and can drive it but when i turn the truck off it will start back for about 45 min. to a hour. I have replaced the fuel filter, fuel regulator, fuel filter, fuel relay. I just dont know what elese to do. Can someone help me with this problem. I think ive spent enough money to buy a brand knew engine. Its been to three differt shops and cant find the problem.
The only thing you haven't replaced yet is the fuel pump. That's one possibility, the other is a kink in the evaporative controls hoses from the tank to the charcoal canister.
There's an easy test and a hard test. The easy test is to drive the truck like you normally would and then before you shut it off, take the gas cap off. If the truck stalls out or starts running rough, you have a fuel pump problem. If nothing happens, shut the truck off and then see if it starts with the gas cap off. If it starts, then you have a kink somwhere in the evap hoses. If it doesn't start, then you have to use the hard test.
The hard test is to hook up a fuel pressure gauge to the injector rail and cycle the key to "Run" (the click just before the motor cranks) and see what pressure comes up. Fuel pressure can be as high as 60psi on GM EFI, so if you have no pressure or very low pressure (less than 35psi) you either have a fuel pump issue or a leak between the fuel pump and the fuel line. The pressure should hold steady; If it leaks down, you have a problem with the check valve in the fuel pump or a leak between the fuel pump and the fuel line.
I have encountered a similar problem several times on GM vehicles. It might not seem possible, but a low battery, like one not charging enough when you are driving can give you a simmilar condition. The 4.3 needs 57 lbs pressure to start. It has only a brief time to come up to that pressure. A slightly weak pump and a slightly low battery combination can cause the vehicle not to start. Sometimes cycling the key on and off several times for 5 seconds or so and then trying to start can be an easy test. Otherwise, the best test is definately a hot pressure test.
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