Hi, I have a 2002 F-250 SD with 100,000 miles. It developed a miss that you can hear at idle, gets worse upon acceleration, and is terrible under load. We brake torqued it in the driveway, and the miss is wicked. We put it on a scanner that reads everything, and it shows nothing is wrong. Check engine light is not on either. So, I go on this forum (cause you guys are awesome) and do a search on misses. Right away, it talks about plugs, and COP boots. I change all of both..and I do an **** job of it, paying close attention to detail. All plugs looked the same, and the boots looked ok, but I changed them all anyways with OEM parts. I take the truck for a short run, and it goes perfect. I even brake torqued it again..no problem. Later, I start it up and can hear the misfire again !!! I put it in gear, and sure enough, IT'S BACK. So, I brake torque it...but heres the weird part...it misses bad till a certain rpm, then clears up and sounds strong. Let off the gas, and its right back to missing again. So I pull each coil connector while its ideling, and EVERY one makes the motor worse. I also looked at my pcv hose, and it looks ok to the naked eye. Any ideas guys ? I'm lost now. Thanks for any assistance !!!

 

Coils themselves. I take it you scanned it again and there were no codes?

 

Also, run some fuel injector cleaner thru the fuel system.

 

Thanks for the replies. I figured if it was a bad coil, that the plug, or plugs would be fouled. They all looked good. Secondly, I figured if it was a coil, the bad one wouldnt have an effect on the motor when I unplugged it..which they all did (made it run worse). Thirdly, I figured if the coil was bad, it wouldnt clear up at high rpms.

I ran 3 bottles of water remover/injector cleaner thru it when this first started.

So...I'm still SOL....lol.

 

sorry could not be more help. How or what did you use to scan it?

 

top of the line MATCO scanner. It said all peramiters were within specs, and no codes (pending included).

 

put a vacumn meter on it? See what kind of vacumn the motor is making?

 

How many miles are on the plugs? I know you said they look the same, but are they worn out.

 

Plugs had about 100k on them...and they looked fair. I replaced them with new motorcraft platinums. So, I go back out there this morning, and one by one, go thru the whole routine again. Thinking I may have missed something, I pull each coil (with new boots) out..pull the boots off...wipe everything down, pull the new plug...inspect, and wipe that down also. Put new di-electric grease on boot ends, replace plugs and coils. Put aircleaner duct back on, and fire it up. Miss is still present at idle, and partial load...then seems to go away when you get into the higher rpms.

 

The same thing happened to me and I replaced the coils and the crank position sensor as well as the plugs. Runs like a sewing maching now..... Mine never thru a code either, check pending codes......it did show mis-fire detected cylinder 8. Only problem it was cyliner 4 (they share a crank journal) I got tired of chasing it so I just did'em all...

 

Tomorrow I'll order a new set of coils. Also, where is the crank position sensor ? Is it fairly easy to change ? Any adjustments needed after the change ? Thanks.

 

not familar with the one, but should be on the front of the motor, by the vibration dampner.

 

I got a set of ACCEL High output coils at Advanced Auto for 36 bucks apiece.... each had a sticker "Warning! Lethal Voltage!"

 

No duh, guess they have to protect people from themselves. Hope that works.

 

any luck tinman, i think im getting the same issue. no miss when cold. misses more the warmer its gets. misses under light load in higher gears, and clears up in high rpms.