1999 F150 4.2 runs fine at idle, takes gas well up to 2000 rpm then gets sluggish and starts popping at throttle body and exhaust. Timing at 0 degrees TDC just installed new timing cover, chain, tensioner, and camshaft sensor. ( also every other sensor, plugs, wires coil pack part of the burnt PCM wire harness, PCM itself and all the relays corresponding to engine and ignition control. OH and had the NEW PCM sent off, and flash vehicle specific. Also already ran a fuel and compression test. Everything is perfect #'s. New fuel and air filter. any suggestions would be great. BTW the engine only has 67,000 miles. STUMPED on this one. Pretty familiar with most Ford engines, never came across this problem. Thanks

 

Sounds like an exhaust restriction or maybe a bad cat.

IIrc some body else had a simular problem and it turned out being some inside the fender where the air intake goes in. At any rate it sounds like it's starving or blocked up.

 

Had a simular problem. Just found that one of my new Motorcraft plugs wasn't firing. At least not under load. Idle was fine. Put my old Bosch back in and everything works great now. Guess Motorcraft isn't that great after all. Never had an out of the box failure with Bosch.

 

OP - Perhaps you hooked up the plug wires wrong.

They don't exactly match the order of the coil pack.

I think 5 & 6 are reversed.

 

yeah im thinking something is up with the exhaust flow.

 

Thanks for your inputs, sorry it took so long to respond. turns out if the the epc( electronic powertrain control ) Solenoid has incorrect output it will cause alot of problems, also universal air intake tubes are too restrictive. corrected these two problems, and my truck runs amazingly. Thanks again.

 

Okay, everyone, here's something you need to watch out for. My '99 4.2 blew a head gasket, let water into the right front cylinder, and bent a rod when I tried to start it. I rebuilt the engine, and it ran like a top for about 3,000 miles. One day, I went to start the engine after it was hot and had been doing some shopping, and it made bad noises. the same head gasket had blown again! Fortunately, it didn't bend a rod this time.
Turns out the right side catalytic converter was clogged. It caused excessive back pressure, and that caused the head gasket to blow.
If your truck has high miles on it (mine has about 270K), be aware of this and watch out for it!