My truck did this last winter, but not really noticeable, now it seems like its getting worse, or it could be that the weather is just getting worse again.

When she is driven when cold, it has a slight buck or hesitation at low RPM's. This goes away when you get into the throttle or warms up and runs like a dream. I'm thinking maybe its not getting enough fuel/oil psi when cold? GPR, GP's all volt/ohm tested good and it fires right up in the morning. Fuel pressure is 63 PSI @ idle. HPOP is full. Fresh Rotella Syn oil. Fuel filter and FPR screen done this summer. No CEL.

I'm sure it could use injector O rings, but would they make this happen? HPOP going out? I don't have a way to test HPOP pressure unless my buddies snap on gauge can read it or does this have to be done with a manual gauge?

Sorry for the novel, but any input is appreciated

 

Have you tried unplugging icp? And driving it I dunno of ipr orings would do
This

 

Yeah, CEL light comes on and it runs like crap

 

Bad IPR O rings usually cause hard starting when its hot.

 

Exhaust Back Pressure Valve (EBPV) still plugged in? Sounds like weather is starting to get cold and it is activating on cold start ups.

 

No, EBPV has been unplugged for a while

 

Tried a different cam sensor thats h
Just a out of no where guess but good to always have extra anyway

 

I doubt it's the CPS, but you never know...nobody heard of anything like this?

 

My truck is doing it. It does it until it gets to about 160-165*. I can't figure out why it does it, but it's only in certain situations. Like going uphill between 1300-1700 RPM. When it does it, I notice ICP fluctuates a few hundred PSI. My IPR is good, o-rings are good, ICP is new, wiring is good, etc. Not sure what's causing mine.

To be clear on whether it's the same symptom... Does it feel like the engine is "jumpy" and the truck starts jerking back and forth until you either try to accelerate more or let off the accelerator? That's what mine is doing. Starts fine cold, runs fine with that exception... I have to wonder if mine is b/c my IAT sensor is gone. In warmer weather it doesn't do it, but now that it's cooling down here, I noticed the truck started doing it again. Did it all last winter, stopped all summer, now starting again with cooler weather.

 

Spot on Travis. Doesn't do it at all during the summer. It did it last winter and I was just getting to know the truck so I figured it was nothing because it was mild and went away when warm. Now it seems like its a bit worse with the cold weather or maybe I'm just more in tune with what the truck is telling me. Whatever it is, it's getting annoying

 

Travis, why is your IAT sensor gone .. where did it go?

As far as a slight bucking, hard to describe, when out on the freeway I must say I did notice something this winter almost like a spark plug misfiring now and then, but only when cruising. Thought it was just bumps in the road but maybe not.

Next week I'll monitor ICP - IPR when going to work and see if any funny numbers pop up.

 

I'm not sure where my IAT sensor went, but it's MIA. LOL It was there when I did the 6637 4 or 5 years ago, but it's gone now. The IAT display on the scan gauge reads a constant like 50* or something whether it's 110* or 15* outside. Not sure how the IAT might effect the running of the engine while cold, but IIRC it does have some effect on fueling when it's cold.

 

Hmmm. Is the IAT that stupid little round plastic thing that looks like it did absolutley nothing on the factory air box? Because mine is gone as well

 

That's it Todd, the funny looking round 'probe' under the 6637.

 

I guess I will have to figure out a way to put it on the 6637 considering Travis and I are having the same problems and the only common denominator is the missing IAT.