I bought my son an old farm truck for his first and because I like F150's. We drove it home with a real rough idle and poor porformance...I expected a good tune up would help. Well, we can barely get it started and haven't driven it for weeks. It blows black smoke out when cranked and will not start. I replaced the pluges, wires, distributer and cap. It ran for about two days and acted up again...black smoke and all. Pulled the plugs and they were fouled. Put new ones in and it ran for a day. What is going on!!!

 

I'd check the cats. Disconnect the exhaust before the cat. converters. If its not that than I'd say the rings.But I'm kinda loaded at the moment.

 

Black smoke is usually caused by over fueling.

Once upon a time, the fuel charcol canisters would fail and fuel would be sucked though a vaccum hose directly into the intake.

Does your truck have a carb or Fuel injection?
carb = Check the choke, choke pull off and then power valve. look for a Vaccum line to bowl vent.
Injectors = There are a number of possible issues that should register a code on the computer. Find someone to read the codes (auto zone does this).

 

It's fuel injected. I pulled the vacumm line from the fuel pressure regulator to the intake mani. and it was pumping gas out! So, I replaced the FPR...had to turn the engine over some, but it started and ran fantastic and zero smoke. Turned it off and drank a coke and started it again...had to turn it over some, but it started and ran great. The next morning it wouldn't start at all and hasn't since. I have spark and also was able to shoot gas out of the snifter valve on the fuel rail while pushing the valve in with a small screw driver...so I figure I have gas. So, I'm really confused now.