Stumped with a bogging/miss issue

[gregstukey]

So, My 4.0 is bogging and eventually threw a P0306 code. So far I've done the plugs (gapped to .061), wires, and coil pack, and fuel filter. So far nothing is getting rid of this "ghost in the machine." When I really baby the throttle it runs fine and throws no code. When I lay into it just a little I get a spuddering sensation and lack of power. If I ease off it it will mellow out. Ive inspected and cleaned the MAF sensor. It also sounds like its backfiring ( a knocking sensation is heard when I lay into the throttle).

Im really lost of where to go next. I hesitate to take it to the dealership cuz I know they will throw the book at me. Can anyone help?

-Greg

 

[Big Jim M]

Put the plug gap back to .054 where it belongs and the plugs will prolly fire.. At .061 the coil must work too hard to fire the plugs and that easily may be your problem.
Big JIm

 

[fordboi415]

you know i had that same exact problem on an f150 i had and it turned out to be a wire had gotten to close to the exhaust manifold and melted it shorting the connection causing it to do exactly what your describing, and i even replaced everything you just mentioned as well

 

[gregstukey]

I will try adjusting the gap. I find it odd that both the service manual and the sticker on the front of my truck would call for a .061-.068 gap and have it be the wrong gap. But at this point ill try anything.

Also, the problem started with oem plugs gappped way beyond the range(from previous owner) , much bigger, and the truck ran great for years. I might also try swapping the plugs to see if the code follows...

any other ideas? My co-worker had a similar problem and it turned out to be a bent valve?!?!?!? I hope I dont have to go there...

-G

 

[Big Jim M]

Strange that I would have the 2002 4.0 in my Ranger and it calls for .054 gap and yours doesn't.. Did you use the Motorcraft AGSF34FP Spark plugs that the engine calls for? Your choice of plugs and the wide gap could easily be the problem..
Big JIm

 

[Big Jim M]

Greg The smallest gap you can run is the easiest on the engine. As long as the gap is wide enough to have combustable fuel in the gap every time the spark occurs, there is no difference in the way the engine runs. WIDER ain't better if you don't need it.
If a .050 gap runs well in an engine there is NO GAIN from running even a .051 gap..much less no gain from running a .065 gap! If the fuel is in the gap the engine will fire.. A wider gap and more fuel in there doesn't make one damn bit of difference.
Big Jim

 

[gregstukey]

10-4. I believe you. When I went to swap the two plugs today at lunch i re-gapped them to .054 and put them back in. Huge difference in running condition. Not totally cured but enough to make me feel like we're on the right track. I will complete the job tomorrow and hope for the best.

What I'm totally blown away by is that I've double checked the year service manual I have and its correct. I double checked what they list as the correct gap and I just cant believe they would list the wrong gap. Its a big discrepancy it seems...

but im stoked im seeing some change in the condition...finally. Thanks Jim. I owe you one.

 

[gregstukey]

it turned out to be a bum plug out of the box. I swapped the suspected bad plug with a new one (in addition to re-gapping to .054) and no more problem. Runs great. Thanks!!!!