CM2250 Poor fuel mileage

[Truckdriven]

I recently put a truck on the road that had been parked for 2 to 3 years before I bought it and now has terrible fuel economy in the 4.5 mpg range. Truck is a 2012 Kenworth W900B Vin 1XKWD49X5CJ324795 Engine serial # 79502726 CPL 3719 18 spd 11r24.5 tires 3.70 rears 633K miles 24,700hrs we pull a 53-foot livestock trailer with a good mix of secondary roads and Interstate running 50/50 loaded 80-85k and empty 33k lbs. Engine was stock until I got it and had it deman dated by R R on this forum and set 500hp 1800tq. One thing I question is the Boost pressure will be about 30 if I let it lug under 1500 rpm (not normal driving habit) and will drop quickly as soon as it's above 1500, about 25 at 1600 and 20 at 1800, is this normal??? Also greatly drops off in power above 1500 compared to our cm570 with same power settings.

Work done in the last 12k miles, vgt rebuilt, overhead set, fuel pump rebuild, new intercooler and all connector boots and clamps, new exhaust press sensor and tube (wasn't plugged), new imap sensor, barometric pressure sensor, fuel rail press sensor, fuel pump solenoid, rod and main bearing, oil pump jacked to 40ish PSI.

Injector leak down test was 900psi drop in a minute first time and 700 second time, 10k ago it was 340.

Yes I know it's aerodynamics don't do it any favors and I'm not looking for 9mpg but in comparison to friends doing the same work with long hood trucks they are 1.5 - 2 mpg ahead of me, even the old CAT guys all beat me and even the vgt deleted isx gets nearly 2 mpg better! (No I won't be doing that)

Could being parked so long have anything to do with it? Like the injectors getting slightly gummy and not functioning properly?? Is my oil pump set to high and adding to much load?? I've done what I know to do and nothing made any difference.

[Truckdriven]

I forgot to mention the exhaust is totally straight pipe

[tree98]

Bad delete?. Your gonna need to pull a copy to send to Rawze.

[Nilao]

If RunningRough did the tune I doubt it's bad....are the parts you replaced OEM or aftermarket?

You could call RunningRough back and have him adjust your turbo mappings, they could be set too low....most of our tables are based off of OEM coolers and such.

No amount of tweaking a tune can overcome a bad part so I would definitely double check the mechanical side.

[Truckdriven]

(02-08-2022 )tree98 Wrote:  Bad delete?. Your gonna need to pull a copy to send to Rawze.

Demandate is done by running rough on this forum I already sent it to Rawze for review and it checked out fine

[tree98]

(02-08-2022 )Nilao Wrote:  If RunningRough did the tune I doubt it's bad

Somehow I missed that in his post ...... right it wouldn't be bad.

[Truckdriven]

(02-08-2022 )Nilao Wrote:  If RunningRough did the tune I doubt it's bad....are the parts you replaced OEM or aftermarket?

You could call RunningRough back and have him adjust your turbo mappings, they could be set too low....most of our tables are based off of OEM coolers and such.

No amount of tweaking a tune can overcome a bad part so I would definitely double check the mechanical side.

I agree with you that you can't tune failed hard parts away. That's why we were hesitant to change the tuning right away plus the fact that this program is in many other trucks with no issues. And yes all parts are genuine OEM cummins or paccar

[Rawze]

fuel mileage problems aside...


A CM2250 should peak at about 36 psi or so boost. If your only getting 30 psi boost then something is wrong.

Just some guesses here ...

* could be an improperly reading exhaust gas pressure sensor, or its circuit from the manifold thru the thermostat housing is clogged up. This can cause both power, boost, and fuel mileage problems, depending on how bad it is.

* Can be that the Turbo is not adjusted high enough in the program for the make/model truck you have.

* Can be that the ecm is holding back power/torque for one reason or another (can be seen by monitoring the 'CBL_Fuel_State' setting to see if it is following the torque curve of the engine, the accelerator pedal.. or if it has a fuel derate of some kind.

* Can be a damaged exhaust turbine in the turbo, an inlet, CAC or exhaust restriction, etc.. (something turbo or air related). Could also be a boost, exhaust manifold, or egr circuit leak somewhere. Can also be the turbo out of calibration, or has issues with its control arm.

* Can be something wrong with the fuel system, not allowing it to get full fuel.

-======

Lower than normal fuel mileage issues can be caused by a thousand different things. Does the trip fuel mileage in the dash match the actual fuel mileage on paper at the pump after it has been reset and run for a week or so?.

[SemiSweet]

I’m sure you have checked or replaced your air filters?