Dannysheppard

Default Shew
Have a 97 f150 4.6 v8 done everything under the moon to it I have two misfired cylinders #3&#7 the trucks shacking and stuff bad going down the road just like a dead miss and takes a lot of throttle to get up hills and to at least get up to speed changed everything plugs,wires checked injectors all good put two new coil packs and still missing in two cylinders I was thinking maybe a burnt valve but I wouldn't think two of them just went out all of a sudden any suggestions at all would be thankful that's!

Zrock

Have you tryed seafoam? maby carboned up on the top end?

knightfire83

The most noticeable similarity in #3 & 7 is that they are right next to each other in the firing order.
Other than that, they are positioned directly opposite each other in the block, and fired by two separate coil packs.

A guy on another forum had your exact problem. Turned out that water had got down into the #7 spark plug hole shorting it out. Computer reported it as two separate cylinders.

In another post, it was stated that the windshield washer nozzles leaked right down those two spark plug wells.

Also, I would check to see if the SP wire locations on the two coils are correct. Make sure that you don't have two SP wires swapped around.

It would be helpful to know the history of this problem, when did it start?

Dannysheppard

Yeah I seafoam my truck at least once a month I put it everywhere. And the 4.6 start just about a week ago I start down the road after it set for two or three day as soon as I press on the throttle it takes it a min to kick in sometimes it just gets worse the more throttle I give it and shakes and stuff goin down the road the computer said it was #3$#7 misfire but when I let it idial I pull each injector plug in and the only ones that down make a diffrence is number 4 and 7 not 3 and 7 Iv switch injectors around to make sure that's not what it is and not completely stumped on this

Dannysheppard

And when I took the old plugs and wires off they was all clean cause I just changed all this stuff around 5 thousand miles ago and all the spark plug wires are where the supost to be when takeing the old ones off just took one off at a time then look at the diagram just to double check

bigmikek

Lets see the plugs from those 2 cyl.

Jbrew

Bingo! You shouldn't use that stuff, not even once lol. Could be a few things, most likely more than one . That's one way to ruin your engine.

First, geezzz, Well fuel first always, change the filter and check pressure, not sure why you haven't done that, but yea.... Further, -I guess I'd pull the plugs if fuel delivery tests pass, that snake oil is hell on them and it's missing. Compression check the cylinders, could easily be valve problems as well ...now. Since it's had pro-longed exposer to that Seafoam sh-t. That stuff will also smoke the O2 sensors and cake the the catalyst honeycomb with deposits, - they get to plugged up and it'll quit running period.

Also with it running the way it and seeing that Seafoam is involved, your taking a big chance with hydro-locking the engine.

Seafoam is one of the worst products to torcher your modular motor with.

JCR 56

I do not understand some people's love for that crappy Seafoam. They must have one hell of an advertising campaign. If you feel you need something in the gas run some Techron through it, and you shouldn't have to do that very often. Jbrew is 100% correct about Seafoam, keep it out of your truck.

Jbrew

So..Do you think I got my point across ?

Perhaps it's a little much ...I just read what I wrote lol.

4.6LManual

Have you checked the 12V control connector to both coil packs? Corrosion, loose, etc... If any of those, clean connections if needed and apply dielectric grease to connector. >> DO NOT use dielectric grease on the high voltage (spark plug) connections.

Check fuel injector connectors too. Good luck!!