On my way home today, I noticed that my truck started running very rough. It almost acted like it was missing. I limped it home, checked the plug wires, started it back up, and it does the same thing. Up until this point, it ran fine. It idles very rough right now as well.

Any suggestions? If I need to provide anymore clarification feel free to let me know.

 

when was the last time it had a full tune up?

 

I know it's been at least 8 months.

 

Is it possible that a sensor going out could cause a truck to run rough, or act like it's misfiring?

 

It's not acting - it IS misfiring. Buy a Haynes manual (PN 36058 w/light blue cover) & a cheap multimeter, and follow the procedure in Ch.5 Sec.5 starting on p.5-5.

Also, read this thread & do it when you have time.

 

I also have a 1989 with a 5.0 that did the same thing 3 months after a complete tune-up. I asked my friend who has a 1992 with a 5.0 and he had the same problem. Turns out it was from an aftermarket cap and rotor on both mine and his. The aftermarket caps do not seal that well. Went staight to Ford and got a Motorcraft one and neither of us has had a problem since. Just my thought on what could be causing the problem.

 

Thanks for the info steve83 and trackerbrent. I actually took my truck to someone earlier this evening, and he's thinking it's the spark plugs. He removed one spark plug wire from the distributor cap, and it started missing even more. He replaced that wire, and removed another one, and there was no change. So it seems that it's definitely time for a tune up. Plugs, wires, cap and rotor will be replaced this weekend. Hopefully that will take care of things.

 

Instead of HOPING, why not take a few minutes to diagnose it? Then you'll KNOW what it takes to fix it.

 

i have a 1989 f250 5.0 265,000mi had the same problem about 1 month ago. replaced cap rotor wires plugs (20 min) now she runs like a top well better than my f-150

 

Question for someone in the know... With the electronic ignition systemson these engines - COP's or Coil Packs - is there a risk of damage by pulling a plug wire while the engine is running?

 

That risk exists regardless of the type of ignition system. It puts too high a voltage inside the coil.

 

One thing to look for also is cross-fire. Had that happen on a 351 before. Just routing the wires per specs fixed it.

 

Good point.

 

Okay Steve, I got off my butt and gave a go at diagnosing the problem.

I pulled the plugs, checked them out, and saw they were all pretty clean, and burning about the same. I put those back in, and took off the distributor cap. Aha! The points inside were pretty scored, along with the rotor. Went to the auto parts store and picked up one of each, along with a fuel filter. Replaced the cap and rotor, and viola! It hesitated when I first started driving it, but then it seemed to clear up. I also noticed my spark knock was still there, but much much less noticeable now. When I got home and put the truck in park, rather than stalling out like usual, it continued running.

The funny thing was, the guy at the parts store told me the cap I got was only a temporary one Anyone hear of anything like this?

 

Maybe he meant it was low-budget crap; designed to fail quickly???