Okay guys, i've got a 300 that has a definate miss to it. I've changed the spark plug wires, plugs, cap and rotor countless times, and the miss WILL NOT go away. It's really starting to **** me off. Any ideas? Right now i'm leaning twards a sticky valve, but i'm not sure. At any rate, any help would be greatly appreciated. Thanks

-Roscoe

 

Compression test!

Vince

 

You could verify you have spark at each plug wire end.
Besides a compression check you could hook up a vacuum tester gauge. That will tell you if the miss is mechanical (valve, ring).

 

My 300 ('89 4wd F150 SWB HiBoy) had the same problem. Went crazy with timing, plugs, fuel octane, (higher compression all cylinders) wiring, etc... finally told my friend mech that wife complained about fuel smell. He noticed a very faint "mist" around #5&6 injectors which explained my wife's complaint. We both laughed. New injectors seem a tad pricy (about +- $85 each) and not matched. My mech-bud told me to not get the local ones, but go to a guy he had taken classes from back east. Got a set of rebuilt, bench-tested, *matched* injectors for about $32/each. Seems the shop owner had been unsatisfied with the injectors he bought at the parts houses, (he uses more electronic test equipment than I've ever heard the names of, and tests for stuff I've never heard about on injectors) so he had set up a rebuild shop at his own garage for his own use, and then the demand forced him into expanding it for guys like us who want each injector spitting the same amount of fuel as it's neighbor.
Anyway, it was a revelation to see the fuel misting into the air, I had dismissed my wife's complaint because there was never any trace of fuel on the block, lines, ground or anywhere. Let that be a lesson; when your wife says there is fuel leaking, start trying to find out where it is 'cause there don't have to be a puddle anywhere. My mech-bud says his wife can smell the neighbor's dog pass methane in the house next door, so he never argues with her when she says she smells something. ;-)

 

check your intake manifold. i have run into more than one 300 with #1 cylnder intake gasket gone. you can isolate by pulling plug wires and confirm by spraying something flamable around the intake flange.

 

...maybe like an aerosol can with carb cleaner or something similar. If you have a leak on the intake side, it will suck in the aerosol and speed up the engine idle. Do it in short squirts where any fittings join. If you find one, look for another on other fittings, vacuum lines, etc.

 

thanks you for clairifing. woulded want someone getting crazy with a bucket of gas...

 

Can hardly hit this keyboard, ROFLMAO!

 

okay guys, its been quite some time since i posted my question, and i wanted to let all of you know that i finally found out what the miss was. My brake booster was leaking. It wasn't a huge leak, but enough to cause a vaccuum leak. Replaced the booster and that miss went away, i was very relieved. Thanks for all your help.

 

Cool!

Vince