1998 F150 4.6 (349k miles) engine misses when pushing on the accelerator to go up even a slight incline. Doesn't happen when cruising. Can't notice it hard acceleration. got a cyl 8 misfire code changed plug & wire. no improvement, changed coil pack, no improvement. Fuel pump went oy. Changed pump and filter. Engine has same symptoms. Just got cyl 5 misfire help that you can provide will be appreciated.

 

The symptoms sound like weak spark to me.

Put a couple bottles of Chevron Techron or Gumout for high mileage engines in the gas and see if that helps. With that kind of miles on the engine, a compression test may be in order.

 

I thought that I posted this yesterday but I can't find it. I have a !998 4.6 (349K miles) that misses when under load. Seems to run fine when cruising on flat highway or when under hard acceleration. Got a #8 cyl misfire code. Replaced plug, plug wire and coil pack. Now getting #5 cyl misfire code. Anyone have any thoughts on what the problem might be? I recently replaced the fuel pump and filter.