What I have:
2003 f250, v10, 165,000 miles.

Problem: missfires,
Acording to the OBD2 sensor it's missfiring on cylinders #1 #3 #6 and
"Missfire on start up (first 1000 revolutions)".

What I've done:
changed all spark plugs
changed all Cops w/boots
Changed injectors from "good" cylinders to bad ones and vice versa (still missfires on cylinders 1,3,6 ) so injectors appear to be good.
checked for spark to plugs ( good).
check for power to injectors (noid light),good
checked the MAF sensor, looks clean and undamaged
battery/alternator ( 12.45v w/car off 14.56 w/car on).

Going to do:
do a vacuum check on the master cylinder. ( to see if there's a leak some where mechanically (valves etc...))

compression check.

Buy a completely new injector to put on a bad cylinder.

!IMPORTANT!.
It happened AS I was driving.( 10mins after startup, right as I was getting on to highway). Also when I replaced the cop on #1 cylinder the missfire went away. another new cop on #6, still missfires. Put the new one from #1 onto #6. #6 still bad #1 still good (eliminate faulty cop). Later, on another start up #1 starts missfiring again. (Back to square one)


So, With all that said. Does anybody have a suggestion of what it could be or have a another test I can do to find out what's wrong. I've been looking at alot of post all arround about missfires and what not. Most of which point to coil packs or plugs (which I've eliminated). Maybe something with the ecu, wiring, a an o2 sensor is sending bad info?

This is my only running vehicle at the moment and have been fortunate to have friends/family that have lend me theirs in the meantime. But I NEED to figure this out asap.

I appreciate your time helping me out. And will reveal results as they occur.

 

What brand of plugs and COPS were used?

 

Motorcraft, stock replacement.

 

I see you mentioned switching the COPS around did you happen to try different plugs in the same cylinders?

 

Yes, I tried on one cylinder. Original plug w/new cop, new plug w/new cop, alternate new plug w/new cop etc..Nuthin...

 

First, make sure your voltage is correct, and that the alternator is charging. Just to make absolutely sure that your power supply is good.

Check the grounds too, a bad ground can cause all sorts of stoopid stuff

Then, sorry to say, check compression. Remember to open the throttle plate.

 

Sound funny, but I replaced my belt, battery terminals, and cleaned up grounds around the engine bay. Put some dielectric grease in all the connections. It made everything a bit smoother, even after fixing my misfires with boots and plugs. Also, I'm getting an extra .5-1vlt to the battery now.

Something that random sucks to t/s.

 

So, I took it down to the shop for a diagnosis $120..... they found coolant in the oil, No compression in #3 cylinder, and low compression on 3 others besides that one.shop wanted $3k to do anything more.

Most likely culprits are: head gaskets, valves, or cracked heads. So, im Gona do a leak down test this weekend, inspect the valves, heads and piston rings. And while I'm there put some new gaskets on it. Will report back when new info arrives.