Having trouble with my van, It is a 99 awd 4.3l Had trouble getting it to run the other day. Finally got it running but it was running really rich and misfiring at full throttle. So I did a complete tune-up and replaced the fuel filter. After doing this still had the same problem. Got it running hooked it up to scanner and there are no codes showing, if it sits overnight it takes forever to crank. But when it does it idles fine if you feather the pedal it will build speed, but if you go full throttle it will backfire through the ignition. Any ideas will be greatly appreciated.

 

Do a fuel pressure check. It sounds like the fuel pump. The fuel pump also has a check valve built in and that could be part of the reason why it is hard to start. It looses pressure while sitting for periods of time.

 

Did a fuel pressure check, it is sitting at 58 psi and holding when throttle up the pressure rises. Wondering could this be a pressure regulator issue. Because sometimes it seems almost flooded and there is a strong odor of fuel.

 

To really check the check valve in the fuel pump you should do the fuel pressure test after sitting overnight and before turning on the key. If it is low at this point and hard to start, the check valve or the fuel pressure regulator is bad. If you read low pressure, turn on the key and see how quickly the pressure goes up.

 

oldchevy you were correct it was the fuel pump.
Thank You