Misfiring HELP!!

[1979supervette]

I own a 2000 frontier 2.4l 2wd. i am having a missfire problem under load between 1300 and 2000 rpm. it is throwing codes p0304 and p0325, cylinder 4 misfire and knock sensor. the truck idles perfect, the misfire is most noticable when taking off slowly. you can feel it misfiring going down the road at about 55, but its not as bad. when in park the engine can be taken through the rpm range slowly with very slight or no misfire at all. i removed the spark plugs and they tell me nothing, all look fine. i removed the distributor cap and it appears fine also, my dad had the truck before me and i think he changed the wires, as they dont look very old. i am at a loss.

[Rev_D21]

Well it would seem that cylinder 4 is where I would point my attention at. Is the wire attached correctly? Is the wire shot? Is the plug malfunctioning? If you have a multimeter I would check the ohms on the plug wire and see how that looks, you could have a bad wire even if it is 'new'.

[1979supervette]

the only reason i didnt run out and get new plugs and wires, is the truck only malfunctions under load. it idles and revs fine until i put it in drive and accelerate slowly. could this still be caused by a plug or wire? i need to check the ohms and see, the plug is attached correctly.

[Rev_D21]

Yeh it could because a weak spark might not be enough to power the truck while under load but do fine while at idle.

[1979supervette]

well it does do fine at hwy speeds, with no real loss of power. also i just figured out that it runs much much better when cold. when the truck is back up to operating temp its back to spuddering. i know i need to check plugs and wires, but im thinking maybe an injector???

[Rev_D21]

Maybe but I'd start simple and work my way up from there. The Frontiers are not known for dying injectors unless they were abused or neglected. I'd start by making sure everything is in its proper place and in good shape tune up wise. Since it's isolated to #4 that makes things a bit easier.