I have a 1989 f150 302 5speed manual. I just put new cap, rotor, plugs, wires, oil, in it. I also put shorty pace setter headers new downpipe (no cats) into a cherry bomb extreme muffler with both pipes coming out the same side BEFOR the rear wheel. It sounds great and i realy want to keep it. The problem im having it ive lost HP and ive lost about 20mph top end. Help!

 

Check timing and recheck the tune up( plug wiring)

 

Check for codes.

 

I have tried to adjust timing. I put a new idel air control valve in because it wouldnt idle when i pushed in the clutch or in nutral. Could most the problem be in my timimg? And my check engine lite came on but it still runs the same? Ive also put a new o2 sensor in.

 

See what code is causing the check engine light and go from there...

 

Check engine light means something is wrong. You are trying to find out what's wrong. The computer is trying to tell you what's wrong. It's trying so hard its flashing a little light at you. It's saying " I know what's wrong. I can help. All you have to do is ask me. ". I think you should check the codes next.

 

How can i check that code?

 

If it were me I'd use the search button and look for "checking codes" and see what comes up from the 87-91 F150 subforum...

Edit: Actually, I just did that and Just Call Me Sean has a pretty detailed thread on it...I'd post up the link but I can't from mobile.

 

X2 there is a detailed sticky on how to check the codes.