I have a '95 F150 short-bed regular-cab with the straight six (4.9, 300) and 5 speed manual. The truck runs great, but if I get on the highway the cel will come on after a few minutes. Once I'm no longer at highway speeds for a few minutes it shuts off so I can't put a scanner on it to see what it is. Any ideas?

Things I've recently changed on the truck are plugs, wires, cap, rotor, oil, oil pan gasket, pcv filter, pcv valve, radiator, thermostat, clutch and cylinders, flywheel, alternator, battery, fuel filter and front brakes. Whew!

 

It has still set a code in memory. Most likely for the EGR system. That is about the only system that comes and goes on the CEL. Pull and post the code for more insight.

 

We actually did check it after the light had shut off and there was no code. I figured it would've stored something too. Maybe the OBD-I is different than OBD-II in that way?

 

Well, changed the O2 sensor and that appears to have been it. Took about a 30 mile round trip on the hwy and no cel. Before it would come on after about 10 miles. Seems to idle a good bit smoother too.

Now all I have left is shocks, motor mounts, and a/c and it'll be mechnically perfect.