CAT C15 /6NZ trouble continues

Thanks Cat SDP for your support.
Questions.
-what do you mean by " loose nut behind the wheel". Which wheel ?
2nd. Bottom gears = No issues. Once I'm up by 15th gear it starts. 18th gear can barely pull a empty trailer on flat ground, as it stumbles pop's and power extremely low.
But shut engine off after an hour, wait 2 minutes and start it again all symptoms are gone for few hours.
Start engine 2x over the weekend and come Monday it runs fairly good.
I can't use 18th gear loaded. But rolling down a hill / grade I can get up to speed and with all gears out pulling strong, and as long as I leave it on 18th and maintain road speed of 65mph++, it will pull great. But the truck needs that help to get to that speed in order for the throttle to respond to pulling it.
It's like around 15th gear is the line. Above it and problems / symptoms increase. And the farther below 15th I down shift ( or when pulling from a stop) the better it pulls.
Zero symptoms at all in low range.
Zero symptoms in 11th gear (1st gear in upper set) zero symptoms in 12th, 13th or 14th gear. 15th starts the symptoms. 16th and here it comes . 17th and power drop very noticeable as is chugging etc.
18th and no throttle response, just popping and stumbling with coolant temps climbing . In summer temps, it's tough to control coolant temps in higher gears.
Is it possible that my ECM has lost programming for fuel in those gears or similar ?
Any help would be grateful.
All my thanks. It's been a long few years chasing this with much warranty work done by CAT and I spent out of pocket, well over $30,000.00, and still I'm no further ahead.
And every time it goes to CAT and they plug into my ECM my truck always runs good for a day to 5 days. Hence the reason so many times I said " I had the truck at CAT and it's been ???3 days and it's symptom free. I think it's fixed"
-and then the problems return and I'm lost again...
Thanks again for your help.

 

CAT SDP...
I just wrote my last thread to you in reply, looked in the mirror to put 2 toothpicks under my eyelids so to make it home, when I found the possible " LOOSE NUT BEHIND THE WHEEL"
Can't believe that went right over my head, but I made it home...
And to confirm. No loose nut behind the wheel, just frustrated nut is all.
I have a disabled daughter with meds over $2,200 / month, and dad now in long term care i pay the bills for, And a family to support , and I'm fighting Cancer and hope to win the battle.
The truck must keep working, as long as I can and hopefully longer so It can be sold for a good dollar when the time comes. This problem weighs heavily on me, and I don't want my family to know it as they worry enough about me already.
Thanks again for your help. Greatly appreciated to all..
Any info on ECM gear fuel programming would be much appreciated.
I was told that each gear is programmed per fuel load and torque based on various data. I simply want to confirm this as it might just be my saving grace to an end.
Have a good night guys.

 

Good morning 062, and thanks for your input.
When you say " water temp sensor" I'm thinking you mean coolant temp sensor, which is one sensor I haven't changed.
( just doubly confirming )
Last weekend I went through my list of changes etc to my 6NZ and found I had not yet changed the air intake temp sensor ( an inch or so to the right of the air intake on drivers side of engine)
So I picked up one.
Another thing that's been on my mind. Both CAT and Peterbilt as well as another independent shop all say I need not calibrate the new THROTTLE POSITION SENSOR installed 18 months ago. Yet when I spoke to the 62 year old CAT tech at CAT Ontario head office, he said last week it 100% must be calibrated when only the sensor is swapped out. " The only time it need not be calibrated is when the entire assembly is replaced (pedal / sensor etc) " which makes perfect sense, seeing as the 2 piece assembly has been separated when the sensor was changed alone.

 

Thanks SWAAN
Unfortunately no. I don't know anyone else with a 2WS or 6NZ to try his / her ECM. But I've already mentioned it to CAT and they said they would forward my request along to upper management.
I will also be writing to CAT head office about it

My 4 year platinum warranty expires Feb this year. The click is ticking