I have a 1989 Ford F150 4.9L with a 5 speed trans. The truck has 177,000 miles on it and the truck has no acceleration power. When starting from a stop the truck feels like its in a high gear and very sluggish. I can only get the truck to about 50MPH and then it like maxs out on speed. I cant get the truck to rev over 3,000 RPM. I have replaced plugs Gapped @ .044, wires, cap/rotor, fuel fitler, took the cat off, new air filter, and put sea foam into the gas. There is no change in the acceleration. The speedometer just recently stopped working. I determind that the cable and guage are still good but the speed snsor is bad. Could this cause the computer to be confused and cause loss of power? Could it be the O2 sensor? Any help would be greatly appreciate and thank you all in advance for any help given. Eric

 

If the O2 sensor has never been replaced, I'd start there.

Have you pulled codes on the computer to see if anything's showing up?

I don't *think* a manual trans is affected by the speed, but I could be wrong. I thought that was just a auto thing.

Lastly, there can be other variables that can cause lack of power issues, such as dragging brakes, a seized parking brake cable, wheel bearings that are seizing up, etc.

 

ok thank you. I checked for a hanging brake and e-brake cable and all checked out good. I want to pull codes from the engine but am not sure where the hook up is? If you could direct me in the right direction would be very helpful. Also, can you pull the codes with a paper clip? Thank you agian, Eric.

 

Your truck should have a speedometer drive gear doesn't it? Didn't think they went to electronic speedos until early 90's but could be wrong.

Like Bronco said, pull the codes first. You can spend a lot of time and money guessing when the computer might very well tell you where to look first. You shold have the OBD1 system. Believe there is a writeup in the sticky's at the top of the forum as to how to pull the codes. Or you can order a reader for about $30, IIRC.

 

Sorry, I've never pulled codes from an EFI 4.9, so hopefully you can find a writeup on it. I just know it is THE first step in diagnosing issues.

 

Here's a writeup on pulling the codes on a pre OBD2 system.
Pulling EEC-IV codes - FSB Forums