Hey guys im new to the site.

I have a 1998 f-150 supercab with the 4.6 triton v8. The check engine light came on and i hooked my tester on it and it came back with a #5 missfire. well i changed the coil the plug wires and the plugs and finnally the injectors and it keeps comeing back as a missfire.. please help me

thanks
sean

 

If the motor actually has a miss? I would hook a noid light up to the injector wire (#5 the one that's missfireing) an make sure your getting a signal from the computer to fire. If it shows to be good, then run a compression check on all cylinders. They all should be within 20% of one another. If that’s good I would do a leak down test. All you need is fuel, fire and air to run but you must have timing to run right!

 

ok so i di do the comp check and it came out to be 50 psi on each cyl. did leak down and it was fine and noid light and it flashed. the i changed the wires again and the sparks plugs and finally an ingector and coil and it still sais misfire on my scan tool.. so im stump.. so you guys have any ideals.. please help me..

 

50 psi is way low. i would exspect 100 psi+. the motor should turn over atleat 3 complete rotations and the psi should rise up with each rototaion. also oil the o-ring on your comp gauge to make sure your getting a tite seal. let me know what you get.

 

Hey guys new to the board,I have a 1997 F150 triton 4.6 it did just what you are describing. I was tooling along it started to loose power and it died. I got it to restart after a while and it has run rough since. Took it to the dealership and they stuck me $750 bucks to change a plug wire new map sensor and some tests and then said oh its the rear cylinder and it has a bad valve or cracked ring so it will have to be rebuilt. Runs like crap bad milage and went from check engine light to a flashing check engine light.
Bummer and bummer again I guess the fix is do the heads and hope that cures it.
84000 miles.

 

on a compression test it should be at least 100 and should stay at the number it will reach after cranking. if it does loose pressure then i would say either a crack of a stuck valve