okay, I've been living with this problem for a while, it's time to get it figured out. I've done a search but haven't found a problem quite like mine.

the truck is a 1999 v10 4x4 auto with 117,000 miles., the problems started around 114,000 miles.

What it does:

Sometimes it runs flawlessly, but then all of a sudden it misses horribly for a random period of time. It's not just a sputtering when accelerating, it won't accelerate. It will not move when it's missing, it barley even idles..If you hit the gas it just get's worse... then randomly, it'll go back to normal. THE CHECK ENGINE LIGHT DOES NOT COME ON.

When the problem first started it wasn't so bad, it would just randomly do it for 20-30 seconds every once in a while. Now it can last days and is much more frequent. The past 3 days it's been running great, but 4 and 5 days ago i couldn't even drive it up the driveway. I've driven it to austin without fail, but on the return trip i spent a good hour on the side of the road waiting for it to return to normal.

I changed the fuel pump and the fuel filter, did nothing.

 

I had A 97 f150 that had a similar prob.... after a few trips to the dealer it turned out to be one bad plug wire..

 

Wire or Coil sounds like. Ours did the same and it never set the CEL or any codes apparently.

 

well while it was running good i unplugged one of the coils and it didn't run that differently, nowhere near as bad *** it does when it messes up. So it would have to be several coils intermittently messing up at the same time... what would cause that???

 

A harness rub for the coil wires on one side of the engine maybe. just a idea or a place to start looking.....

 

everything looked pretty normal

 

bump bump bump

 

When is the last time you replaced your spark plugs and COP boots? Just because the CEL didn't come on doesn't mean it didn't throw any codes. Check for DTCs.

 

OOoooo, COP boots, Yeah, Good Idea!! Look for carbon tracks on the rubber boots, If you see some, the spark is arcing to the side sparkplug hole, instead of the spark plug. That condition can be intermittent easliy.

Good Call, dkf!

 

*****,

There is a few miles since it started to act up on you, but if you have maybe washed or pressure washed your engine or live in a wet or snowy climate there is a chance you have some moisture in a spark plug tunnel/hole.
I realize it's a long shot, but it's possible. It might be worth popping off the coils and boots one at a time to look for even he SLIGHTEST amount of moisture on the boots or in the plug holes. If you find any signs of moisture give that cylinder a good blast of air or manually clean (dry) it out.

Rick...

 

where do the carbon tracks look like? I've never looked for them before

can a coil intermittently work and not work? if not i bet it's arcing, that does seem like the most plausible explanation.

the back two cylinder's on the passenger side look like a bitch, i have giant forearms, lol.

if it's dark outside and the problem starts, would i see the arcing? I've never thought to look before.

 

and of course it never has the problem when i'm trying to diagnose it, it's been running fine for 4 days.

 

Coils can act stupid sometimes but I would rule out the COP boots and plugs first. I bet your 99' probably never had the boots replaced and they are probably bad, the plugs are probably junk too. The COP boots is what keeps the elements out and seals the space between the coil and the plug.

The plugs and boots are deep into valve cover and head and the coil sits on top of them, good luck even trying to see a spark, especially since the valve covers are plastic. Plastic don't conduct electricity too well.

 

Balls2thewall, you should be able to see pinholes in the boots that look 'powdery' black. If you rub those spots, you will get the carbon from the little bit of rubber that burns with every arc to the side of the spark plug well. Also, you may see where they have melted or burned if it severe enough.

 

thanks guys. i'll change all my boots and plugs and let you know what happens. the boots look pretty good though, they may have been replaced.