Just started about 100 miles ago. When cruising at light throttle and 30 mph or so truck has a miss/buck, between 1200-1800 rpm. I can also duplicate miss in park at those rpms. Once past those rpms truck runs fine. No check engine light and no codes or smoke.
Truck has 236K on stock injectors. Changed valve cover gasket, uvch and glow plugs(all motorcraft parts) 1k miles ago. Thought IPR was sticking due to IPR % @ 40 when cranking(but no problem starting) changed it anyways (motorcraft) and still reads around 40. Also switched to Delo 5w-40 oil. Both were changed about 200 miles ago. Also buzz tested injectors and all were good electrically and sounded normal. No oil on ICP sensor and fuel/filter in bowl have no signs of oil. Im thinking injector oring or worn poppet since it didnt start until after switching to synthetic. Pulling valve covers this weekend to check for leaking injectors and oil return from deflector spouts.

 

Sound like iinjector orings leaking.

 

I swear I have read a failing ICP can cause incorrect pressure readings back to the PCM causing that. This sticks in my mind as I was reading about its function as mine is leaking oil and needs replacement.

 

inj orings leaking is an easy test, fuel filter black or remove VC and see if leaking by
Faulty wiring to IPR, ICP bad and a sticking IPR can od it from what I have read.


With out a scanner, its tough to pin point it

 

Leaking o-ring on an injector won't cause a buck or stumble of a single injector. It might cause an overall drop in the high pressure oil, but that's it.
A buck or stumble is typically a solenoid or Poppet Valve issue. Sometimes this can be resolved in a rebuild and sometimes not. And typically we can't find this issue on the flow bench, just too many parameters constantly changing when you drive that we can't replicate on the flow bench.
It's best if you can narrow it down to an injector, and deal with that one only and make sure the problem goes away.

 

Thanks for that info DZL JIM. Im pulling valve covers this weekend to check armature clearance and poppet screws along with leaking injectors and oil spout spitting oil. What do you recommend the best way to narrow it down to an injector? In park I can get to the RPM to duplicate the stutter.

 

If the issue is a rapid RPM variation and not just a "miss" on one cylinder, it can also be an issue with the drive by wire sensor on the throttle pedal. We had a 7.3 bucket truck at work that did that for a while, but it was less related to the RPM than it was the pedal position. I would say that if it is definitely related to that particular speed, and not a pedal position (which would probably be a different RPM loaded versus unloaded) it's probably not the pedal. Just something else to consider.

 

A break out box is extremely handy for stuff like this.
Make it stumble, and start shutting injectors off one at a time. Once you find the injector that does not make it stumble worse, swap the solenoid with one next to it, and test again. See if issue moves with the solenoid. If not, then move the entire injector with the one next it, test again. This is needed to eliminate any wiring, IDM, etc.

 

I pulled covers and unplugged each injector one at a time both at idle and at rpms causing problem and with each, the engine stumbles as should so power to injectors are good. All oil spouts are showing equal return across all 8. Threw in a known working CPS since I had one and no change.

 

You have to get it in the rpm range that makes it stumble, and make it stumble.
You can't do that with the vc off or you'll make an oily mess.
A Break-outbox is really the only way to narrow it down.

 

I did that exact procedure DZL JIM and was actually a pretty clean procedure . Had someone rev to the rpm to duplicate stumble and compared each injectors oil flow. Disconnected each injector one by one, same as a breakout box would do, and each injector caused the engine to stumble/miss as should and they also performed the exact same visually. Couldnt pinpoint a single injector since the truck runs more rough when disconnecting a single injector than the vibration im trying to troubleshoot.

 

Well, not sure what else to try then. It doesn't sound like a specific injector issue.
Are you sure your HPOil flow is good and consistent? Like, get it to stumble and see what IPR DC and ICP psi are doing?
Are you able to see what fuel pressure is doing when it stumbles?