I have a 1990 F-150 with a 5.0 with 97,000 miles. It has been using excessive fuel amounts (10MPG)and has a miss while idling or you can feel it while driving. I have had it to two Ford garages,one independent shop and all say they can't find it showing any codes indicating a problem. I've replace the EGG sensor(not the valve),throttle position sensor,thermostate,one fuel pump,wires,plugs,cap,rotor,fuel filter,and one exhaust manifold,none of which have done the trick. The reason I cahnged the exhaust manifold was because it was broken and the leak was causing the sensor reading to be wrong according to the Ford shop. Makes sense. Right after I changed it it seemed to run good for about two days. After that right back to the same old thing. I found out that the new exhaust manifold was leaking and I had the dealer install a gasket this time between the block and the manifold. This time nothing changed and it was back to missing again. All this work and still nothing. I'm about to just sell the thing. Any Suggestions? HELP!!

 

After replacing all those parts, the only thing I can think of to cause a miss would be a faulty/plugged injector, or bad injector wiring. Also, I'm not sure, but I'm thinking a plugged up catylitic converter could cause problems like yours. I had a similar problem on my truck which is also a '90, but a basic tune up, fixed it right up. Hope you figure it out.

 

My Dad had the same truck in 4x4, 5spd. (104,000 mi) I know you changed plug wires. So did my Dad. His would rev to 5000 RPM like it was in a mustang and start/idle great. But when it would go up the slightest grade it would miss and ping and make a nice rattle. After checking everything else it turned out to be a bad (new) plug wire.
Don't give up; double check everything. Watch for cracked manifolds. They might show up around 100,000mi...

 

>After replacing all those parts, the only
>thing I can think of to
>cause a miss would be a
>faulty/plugged injector, or bad injector wiring.
> Also, I'm not sure, but
>I'm thinking a plugged up catylitic
>converter could cause problems like yours.
> I had a similar problem
>on my truck which is also
>a '90, but a basic tune
>up, fixed it right up.
>Hope you figure it out.

Thanks for the reply. Would a plugged converter or injector show up on a smog test? I had the truck smog tested twice one guy said it was bad the other nothing was wrong.