I own a 1990 F-150 4x4 with the 302CI 5.0L engine, which is electronically fuel injected. Ever since I've had the truck ( about 6 months) the engine has missed under a load. The truck runs fine until it is under a load. I have replaced the PCV valve, air filter, spark plugs and wires, distributor cap, and rotor button. None of these seemed to help any. The truck gets poor gas mileage ( about 11 mpg). I thought it may have been the fuel injectors so I ran it with some STP fuel injector cleaner a few times. that still didn't work. I have checked the vacuum and it is fine. Does anyone know what might be wrong?

 

dirty fuel filter? Low fuel pressure? incorrect gapped sparkplugs or a loose wire? easy things to check. May want to have tested the Ing. coil or the ICM which is located on the distub. Almost all autoparts store will check thiese for you for free.

 

If the fuel injectors are already really dirty, you could run 3 cases of the over-the-counter bottled stuff through them and it wouldn't help. I just had to have mine cleaned, along with new intake manifold gaskets and a MAP sensor.

 

Check the valve timing - your chain may have jumped a tooth.

 

Thank you for all the replies. I forgot to add that I also replaced the fuel pump with a new one because the fuel pressure was low, I also replaced the fuel filter. I have already used that fuel injector cleaner 3 or 4 times. It did help some, but didn't get rid of the miss. I am almost wondering if something is wrong with the computer chip or system. Have these been known to fail or be defective on these trucks? Could I have a fuel injector out that may be causing it to miss?

 

check the EEC modual on the distributor

 

The EEC is installed thru the firewall below the L hood hinge - that's the TFI ignition module on the distributor.

 

your absolutly right steve..Im in the middle of trouble shooting two fords (one 86 f-250 4x4 and one 1990 f150 4x4) and they are NOT making it easy on me , as such I had parts on the brain so forgive me

 

Be sure that the #7 and #8 plug wires are separated as far as possible. They are known to crossfire on some 302's.

 

I'm going trough the same problem with my 88 F150 302 M5 4x4 31x10.5, 4:10s cept mine only misses a little during idle, then again when I make an early shift from 3rd to 4th or 4th to 5th it will miss, till I get the revs up past 2000rpm then smooth as can be. Fuel mileage less than 10gal per mile.

But there's some history to my truck. The guy I bought it off had the engine rebuilt 40,000 klms before I bought it he gave me the receipt (work order). I called the shop that did the rebuild. And the owner said it was an under the table after hours job buy one of his former mech's, but assured me that that motor should run strong for a lot of miles and run circles around any truck around. So I ask him what's in it for internal components, he doesn't know for sure? but can find out for me. He said the guy I bought it off didn't spare a dime on parts. When I bought it the guy told me he took off all the hypo ignition stuff, coil,wires cape,rotor, ect.... And put stock Ford stuff on( he kept it all for his other F150 2x4 slammed with some kind of SS thing going on) Now it does run like a banshee (she'll cherp the tires all the way up to 4th gear shifting at less than 3000rpm ) but she just developed this miss under 2000rpm once the weather got warmer. I went and purchased an MSD coil,cap, Accel wires, and a new Ford TPS and fuel relay. Now the plugs are a different story the standard size spark plugs I usually buy for a 302 wont fit ? I'm going to investigate a little more into this plug thing tomorrow.

Different heads?
Oh ya it also has true Mustang stainless headers? and 3 inch single exhaust,some kind of dyna flow muffler and high flow cat

Engine #s match truck.