I have a 91 f150 with 300 6cyl.. months ago it got where it would not crank and idle. after a fuel pump,filter,2 fuel relays,fuel pressure valve,they say it was computer, so new computer well it cranks and idles all day if you want to,but when you put it in gear and put a load on the engine it is like its running or 3 or 4 cylinders. idles great .I figured it needed running so i took it for a 20 -30 mile run and same thing idles great runs bad also forgot it has new plugs and wires also any help would be welcome... maybe bad computer??. thanks Danny

 

Fuel filter? Vacuum hose disconnected? Lots of possibilities but those are the first that come to mind. I would guess it's not the computer. More likely a vacuum problem. Did you check the compression? Good luck.

 

Might try one last thing before going with another ECM. CHeck your timing - if someone worked on it and forgot to reconnect the spout connector, or didn't disconnect it and timed it you could have symptoms similiar to what your having. A long shot, but should only take five minutes even if it's wrong.

 

Moved from 3.0L V6 Forum