I have a pretty strange issue. My 1993 F-150 XL 4.9l L6 starts up fine (most of the time), but I’ve been having an issue when I accelerate. When I put the pedal to the floor all it does is sputter. It’s gotten so bad that sometimes the vehicle won’t go faster than 5mph on occasion. It usually only gets bad when it’s warmed up, but lately it’s been having issues immediately. I’ll tell you what I’ve done to try and fix it:
• New fuel pump
• New fuel hanger
• New fuel filter
• New spark plugs
• New TPS
• New MAP sensor
• Fixed vacuum leak

i really have no idea what the problem could be.

 

I would check fuel pressure, should be 45-60 psi. Do you have any raw fuel coming out of the vacuum fitting on your fuel pressure regulator? Any codes? How's the rest of the ignition system? At night, spray down the wires and cap to see if there is any arcing. Check the cap and coil for cracks and carbon tracking. Check the resistance of the coil. Hang a vacuum gauge off the manifold. Do you have 18-22 inches? When you increase the throttle, does vacuum momentarily drop then go back up as it should? If the vacuum drops down and stays low, that could indicate an exhaust restriction. You have spent enough of your money on parts guessing, now its time to test and diagnose.

 

I have had vehicles with a defective coil do this. They will not handle the load when the throttle is depressed. If coil is original, worth looking into..

 

Im having a similar yet different issue with my 06 XLT 2 valve 4.6. My question is can water splashing up on the coil pacs cause an issue with them??

 

Check the trottle body mounting gasket
They have been known to blow out on the inner mounting side