I have a 1998 F150, 4.6 I bought wrecked. It had been sitting up for about 3 years. As soon as I put a battery on it, it started immediately, but I can't seem to get it to run right. It has no power. It idles ok, but you have to apply the gas very slowly and it runs like it's under a constant load, like the timing is very slow or something. I've removed the fuel tank, cleaned it and replaced the fuel pump, sock filter, and fuel filter. I've changed every sensor on the engine. I've changed the 2 coil packs. I've changed the fuel pressure regulator. I've had it to our local Ford dealership and they hooked it up to about 3 different computers, and told me all the electronics check out fine. They didn't know what else to tell me other than to remove the intake manifold and check everything there. I did that. Everything seems to be fine, no cracks, no bad gaskets, etc. Now they're telling me I should remove the heads and check all the valves but I see no reason to do that. I ran a compression check on each cylinder while the intake was off and all the cylinders run between 110 and 120 psi.

I'm at a total loss. I for sure can't afford to put it in an expensive shop and let someone play trial and error. Any suggestions out there?

 

could you have excessive exhaust backpressure? collapsed cats maybe? i'm assuming you have new air filter, correct ignition timing, brakes arent in a bind, egr is ok, no vacuum leaks. good luck, let us know when you figure it out.

 

My first guess is plugged exhaust too like 03f150man said. I'd unbolt the pipes from the manifolds and let them drop down as far as they can and see what it runs like then.

 

It was a blocked exhaust. The truck had been hit on the right side, and the exhaust had been knocked over against the transmission case. This obviously broke everything loose inside the first cat, which stopped up the second cat.

Thanks again for your input, guys!!

 

Thanks for letting us know what you found