My brothers 97 F150 with the 4.6 V8 has a slight hesitation when you are on the gas pretty good? I am not to sure what it could be. The spark plugs have never been changed, but it only has 45000 miles on it. I guess it goes 100000 miles before plug changes. I was going to pull them out and check them out to make sure. This is only the second problem in the engine compartment. The first was when my dad owned it and he was driving along up a hill and it started to run like crap and the check engine light came on. He took it right to the dealer and it had a spark plug wire come off. Now it has a slight hesitation under load. Thats all the problems it has had. Its been a real runner. Anybody have any similar problems? Any ideas. Its so hard to say with these computer controlled things. so many sensors and stuff. He never got a check engine light either. A buddy at work has an OBD2 reader. Maybe it sotred some trouble codes. Thanks for any help

 

That's not many miles for a 97. I would say it is probably carboned up. Here are two options to clean up the ring pack valves and injectors.

1) clean the engine with Auto-RX, and the injectors with Scheaffer's Neutra 131.

2) Clean the engine with Lube Controll, and the injectors with Fuel power.

Auto-RX, Lube Control, and Fuel Power all have special offers going until either Dec 25 or 31.

 

My 97 4.6L did the same exact thing. it would only hesitate under load, but eventually it started a rough idle. it turned out to be the upstream O2 sensor, bank1.

i replaced a ton of stuff before i found it: IAC valve, PVC, TPS, EGR, Plugs and wires.

its worth looking into the O2 sensors, goto autozone they're $50 a piece.