I know this topic has been gone over a bunch of times. Trying to figure out if my 1995 f150 xl 4.9 single cab 4x4 5 speed m502-r2 is Air in the head or Air in the manifold. Trying to buy a junkyard motor. Tired of messing with my motor. Cant figure out why it keeps misfiring and sputtering real bad.

 

What kind of maintenance have you done so far ?

 

Brand new durlast gold distributor, new motorcraft spark plugs n wires. Oil change. Fuel filter and oil filter. Added a new walker y pipe so I dont have an exhaust leak anymore.. not sure what else to do.

 

Replace the engine??? That's extreme. Hang a fuel pressure gauge on and verify you have 30-45 psi.Make sure you have no raw fuel present at the vacuum line of the fuel pressure regulator. Hang a vacuum gauge on and verify you have a steady 18-22 inches of manifold vacuum. Increase the engine speed, you want vacuum to momentarily drop then jump back up. If it falls low and stays there, look for a restricted exhaust. Check these and report back with your findings.