I have a 2000 f150 with the 5.4L, it has 120k miles. I've replaced the fuel filter, and the catalytic converter and new coils. I bought it with an aftermarket air filter and exhaust. The truck is having trouble going up hill and maintianing highway speeds. The acceleration is horrible as well. I was on the highway doing 70 down hill and went all the way down to 40 when I went up hill. The engine is seems to be working extra hard to maintain the speeds I need. What should I try fixing first?

 

 

Changing the coils won't do a thing if the plugs are no good, and since it has an aftermarket filter, the seal could have be terrible on it allowing unfiltered air past it allowing dirt and debri into/onto the mass air flow sensor. Check the condition and gap of the plugs and replace if necessary, If you replace them, check the gap before installing, Inspect the MAF sensor and clean/replace if necessary. I would also inspect the PCV valve as well.

 

It won't go up the hill if it can't suck any air. Check the filter.

 

 

If the engine is racing but you arent moving and you have no codes then I would look at changing trans fluid and filter, but first pull your trans dipstick after allowing it to warm up and after shifting through the gears to check the level. You can do this at a stand still in your driveway truck doesnt actually have to move. The fluid should be bright red. If it is dark and smells burnt you may be in good shape after the change. Do not let anyone "flush" it unless you really want to take a chance on replacing it soon.