1997 f150 misfire

[nesralyrrej]

97 f150 4.6, misfire randomly starts and shakes the truck pretty bad, my scanner says cylinder 4 and 7, so I started with what everyone would. Plugs and wires, no change, replaced coil packs, no change, replaced maf, no change, replaced the pcm, seemed to rub better for about 12 miles and started shaking again. I know on the Mustangs and Lincoln's can have the icm's go out and it will fire paired cylinders at the same time (4 and 7 are paired) the f150's don't have serviceable icm's. So I'm beginning to think.. Maybe worn wires that are touching something they shouldn't at random unpredictable intervals. I'm losing my mind here guys, get back to me!

 

[RonD]

Yes, that 4 and 7 is too much to ignore, 4 and 7 are suppose to fire at the same time, it is a Waste spark system.

I would get an old time timing light and hook it to the 4 or 7 spark plug wire to see if your suspicions are correct, should see a steady spark pulse from timing light while engine is running, if not then that coil is not getting proper ground cut and connect signal from the ICM in the PCM.

It could be that Ground wire is chafed and grounding out so coil doesn't fire.


4.6l firing order 1-3-7-2-6-5-4-8, split it in half and put one half below the other
1-3-7-2-
6-5-4-8

1/6, 3/5, 7/4, 2/8 are the pair cylinders, both cylinders get spark at the same time with a Waste spark system

 

[nesralyrrej]

Rond, been helping me since I got on this website! So if I get inconsistent spark it could maybe be the ground wire rubbed through.. I'll check that in the morning. Are there problem spots in the truck 4.6?