Dear Ole Mechanic;
I have a 98 Chevy one-ton with a 454 gas engine. It doesn’t even have 50,000 miles on it, yet because it is used only when I tow something or am hauling a heavy load. I have a much more fuel efficient smaller vehicle for general running around.
The 98 runs great, gets reasonable fuel mileage when towing and starts great when it is cold. It just doesn't want to start when it is hot. It cranks and cranks and will finally start. Once started, it is OK. Let it sit till the engine cools down completely, and it starts right up--no problem. It has never failed to start when hot, but it sure seems to crank a long time--long enough for me to wonder if it actually is going to start. A friend of mine noticed that just after it started when hot, a puff of black smoke came out of the tail pipe. Do you have any suggestions or any idea as tp what's going on?
Cranky when Hot
Normally I would suggest that you check or have checked, the electric fuel pump in the gas tank. A hard-start condition situation usually is an indication that the pump is starting to fail. The in-tank pumps on Chevy and GMC trucks do not have the best reputations for long life. However, if the pump is starting to fail, it generally shows up as a hard-start or no-start when cold but not as bad when hot. A hard-start or no-start when hot and cold could be due to a wiring problem that prevents the fuel pump from working until the oil pressure switch signals to the computer that there is engine oil pressure. I don’t think that is your problem, as there would not be black smoke coming out of the tail pipe. Black smoke indicates a rich gas mixture. With the fuel pump not running, there would be a lean condition that would not produce smoke. The fuel-pressure regulator might be leaking fuel back into the gas tank, but that too would also cause a lean condition and no black smoke.
I suspect that your problem is one or more leaking fuel injectors. After you shut the engine off, a leaky injector or injectors would allow the fuel pressure, that should stay in the injector fuel supply line to drop by leaking through the injector or injectors into the intake manifold. This causes a very rich fuel and air mixture in the intake manifold. If the engine is allowed to cool down, the rich mixture is just fine for a cold start. However, for a hot start, the mixture would be too rich and cause a lot of cranking till the rich mixture was overcome and blown out the tail pipe as black smoke. About the easiest way to check for a leaky injector is to put a pressure gauge on the fuel supply line, run the truck, shut it off and watch the gauge to see if the pressure decreases. If it does, then all that needs to be done is to figure out which injector or injectors are leaking. Is there an easy way to do that? Not that I know of with out having about $2,000 worth of test equipment. Even with expensive test equipment, you could only look to see if one or more cylinders are showing excessive misfire and that might not show up due to the normal running after starting. Even an overly-rich trouble code could only narrow the problem down to one side or bank of cylinders. It is still going to be a guessing game as to which injector or injectors are bad. The injectors in your truck’s engine are hidden under part of the intake manifold. You could check the spark plugs and see if one is showing a rich condition, but I doubt that you will find that, as normal running after the start would tend to clean away any rich deposits. Since replacing a fuel injector requires a fair amount of disassembly, it is not something that I would undertake without a more positive identification of the bad injector or injectors. You could just replace all of the fuel injectors, but the injectors would cost over $500, with additional charges or labor, gaskets, etc.. A GM truck dealer should have an injector-cleaning tool that puts a strong cleaning solution through the injectors, but that job would cost $150 or more. My suggestion would be to start with a double dose of aftermarket “Fuel Injector Cleaner” added to the gas tank. Most auto-parts stores have several brands on the shelf. I would try doubling the recommended amount of cleaner for at least two tank fill-ups of gas. If that doesn’t work, then you can start considering repair shop and dealership options.
You could also wait till the injector or injectors leak enough fuel to foul their respective spark plugs. That would tell you which injector or injectors are bad. Just don’t wait until the raw fuel turns the catalytic converter red hot while running. That will just add to the repair bill.
Herr Professor Nuzanbolts