2000 F250 6.8L V10 4x4 (because I know you will want it and I haven't been able to figure out how to signature line it )

Hi All,
I know this is not a new topic and it's been discussed all over the place but I'm no further ahead and have potentially a few oddities I'd like some insight into.
As the title indicates I have the rough idle, missing while driving down the road and vibration while pulling hills etc. The problem has gotten progressively worse over time and tonight it was particularly bad.
I've tried many things as suggested here on the forums:
- I found the PCV valve hose to the throttle body had a hole worn in it - I replaced it as well as the PCV for good measure, no change.
- I replaced all the plugs with new Motocraft plugs - no change.
- I inspected (did not replace) the boots and springs between the COP and the spark plugs - they all looked new with no indications of arcing or holes. (I know this is not definitive but they looked so clean....if I'm insane let me know!)

So here is where things get weird:
- Unplug the injectors one at a time and listen for when the idle does not change. This will indicate which plug is not working....simple right?
- Wrong! NONE of the injectors made any change to the idle when it was unplugged!! How does this make sense? What am I missing?

After unplugging 7 of the 10 injectors (more on that in a bit) I noticed it was idling very smoothly. So I took it for a spin. All the issues are gone! The particular problem areas where it used to lug, miss and vibrate like crazy are now gone...huh?
More on the injector plugs now.....In pulling the power plug off the injector i noticed on 6 of the ones I pulled that the retention tab (built into the electrical connector to hold it securely in place) was missing or just sitting in the connector doing nothing - in other words, there was no retention on the clip. Is is possible that in pulling and plugging back in that one of injector connectors was loose and got properly reseated during this exercise? It's the only thing that makes any sense to me.

So the bottom line: I'm not convinced it's fixed - I'll post more in the coming days in the form of updates. Also, does anyone have any experience in replacing these 2-pin injector power connectors and does anyone have any idea where to get them? IF it turns out this is the issue it's going to come back when they wiggle loose again.

Fire away oh knowledgeable ones....let me know your thoughts because I'm out of ideas!
Thanks in advance. Ask any questions and I'll do my best to answer them.
Wayne.

 

Engines vibrate and if it's and old truck with worn motor mounts it will vibrate even more, so it is perfectly logical that the injector harnesses didn't not send the CPU signal to the injector. I believe you can order new injector harnesses from RockAuto.

-- Dave

 

Thanks for the reply Dave, I appreciate it.
Since I've reseated the injector power plugs the truck has run really well, no misses, no hesitations. Its been about 50 miles.
I took a peek at RockAuto per your suggestion and have new harnesses coming - thanks!
The idea that a harness was backed off from age and vibration makes total sense. What I still can't wrap my mind around is why there was no difference in the idle when I unplugged multiple different ones.
Perhaps we'll never know...in the meantime, harnesses should be here next week. I'll post an update when I have them installed.
Thanks again!
Wayne.

 

.

Thanks for your input, my 2001 has the same issue that has gotten progressively worse to the point I didn't think I would get home pulling a work trailer. I have installed new plugs and PVC also and purchased New Mass Air Flow Sensor (installed), Idle Air Control Valve, and Throttle Body Sensor (just arrived from RockAuto). Going to follow suit with injectors. Thanks again.

 

My first guess would be that you have a vacuum leak.

 

Hopefully this is your problem as well. Since I went through that exercise the truck has run without a miss. The new injector harnesses just showed up last night, I hope to put them on in the coming week.
I suspected a vacuum leak as well at one point but since this has been running so well now I'm thinking that isn't an issue after all.
I will post an update after I replace the connectors and have a few miles on it.
Thanks and good luck!

 

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