QuestionMy 2000 GMC Sierra Pick up 5.3 liter starts perfectly when the motor is cold. Once it has been running then sits from 1/2 to 4 hours, it does not want to start unless I press the accelerator. I have replaced the fuel filter, cleaned the injectors, cleaned the throttle body, added Sure Foam to gas tank as well as 1/2 can Sure Foam to throttle body intake. I was told the intake was carboned up. The spark plugs looked clean, but I replaced them anyway. The fuel line pressure at the fuel rail is 60#. My truck has 68,000 miles. Do you have any suggestions?
AnswerI am not an expert on gasoline fuel injection systems, but I have worked on some over the last 20 years.
I suspect that you are losing fuel pressure after the vehicle is shut off. A 1985 Toyota Celica I worked on did the very same thing. It turned out to be a check valve in the fuel pump in the fuel tank.
Your problem may be that, if your pump has a check valve, or leaky injectors, or a defective fuel pressure regulator (which, when hot, bleeds off the fuel pressure).
The reason that you do not have the problem with a cold engine is that there is additional fuel supplied to compensate for a cold engine. It may also be true that the fuel pump is turned on immediately during a cold start but not during a hot start.
Try checking the fuel pressure after the engine sits for half an hour after being run as you normally drive it. I think that it will be low.
