user fuel state derate?

[Kryptic361]

Hi all,

So ive got a weird one going on thats got me and the local stealership 100% baffled.

2007 Peterbilt 386 isx cm870 ( demandated ) but i think the issue is older than the demandate.

Truck always seemed low on power. Im not one to race to the top of hills but the truck just has always felt sluggish and never boosted to spec.

here is the story of all thats been replaced and repaired and such.

purchased truck. eaton 10 spd installed cause it had a non overdrive unit in it ( parameters changed to correct from FR to FRO trans)
Turbo VGT was locked up so
New turbo
new manifold gaskets

that helped the low boost but still not fixed.

Had factory calibration loaded into ECM ( someone swapped ECM before i owned truck and was wrong CAL and CPL # )

still boost issue and only producing 22 lbs no matter what. but would randomly spike to 35 lbs rarely but instantly go back to 22 lbs

Performed EGR tune up and replaced intake manifold pressure, manifold air temp, Delta P, Baro, Exhaust Pressure, EGR Temp ( just replaced sensors out of no known history of them and age)

Boost issue and sluggish feel persisted.

sent truck to dealership. replaced VGT Actuator and the VGT control Box. problem still persisted.

They said it MIGHT be an ECM. i had a spare ECM on the shelf so i had my CAL installed and put it on. EXACT same issues. zero change.

pressure tested intake for leaks zero leaks found
exhaust has new mufflers and no restrictions.

truck ran but just sluggish.

fast forward some time.

EGR cooler pops

truck by my choice gets demandated

ill get hate for this but whats done is done right now.

non vgt turbo and manifold installed. cooler and all egr piping removed and put into a box upstairs in storage.

at this time overhead is ran.

ran injector leak test with cummins tool ( Thanks Rawze for the video) all injectors pass test no leaks.

also has new fuel pressure sensor and gear drive fuel pump.


now onto what ive found with insite recently

after demandate it really has ran bad so bad that i am now renting a truck until i get this figured out because i dont wanna blow up my engine.

cant build boost over 20 lbs no matter how much you load it up or how much you push pedal down.

egts never get over 800*

truck at idle seems to have the slightest little stutter every now and then. i pulled the actuators apart and cleaned them as well. but found no gunk in them

in insite i was doing some data log for myself and the "tuner"

noticed that the gear down protection was always "ACTIVE - HEAVY LOAD" even tho its turned off in the parameters and features.

Also the USER FUEL STATE will randomly jump to " engine protection derate" "ALtitude derate" and the truck WILL NOT fuel over 54% fuel even tho the pedal is at 100%

I have combed over the Engine and OEM harnesses pulled them apart at the cab and each senor, cleaned and dried each. made sure all my grounds are clean. found a rub spot on the OEM harness but no corrosion ( still fixed and tied up harness better anyway)

anyway so im out of ideas on what to check idk if its tuning related or an actual truck issue.

thru all of this the truck has never thrown an engine code for anything other than the EGR valve position failure ( no longer there after demandate )

i watched the tuner in calterm turn off only the VGT and EGR codes for sensors being unplugged or a component not there after the demandate

Im not out to be the fastest truck on the internet nor do i wanna be the first to the top of the hills i just want this truck to be reliable and have the least amount of parts able to fail on the road that will put me on the back of a wrecker.

i hope this is enough information to maybe spark something in someones brain as mine is about fried over this one and i am no longer taking it to the dealership. i think they just threw the parts cannon at it anyway .

and thank you for taking the time to read this long winded explanation of my issue.