Anybody lost fuel mileage after demandated

[n2racing]

I have 2014 peterbuilt 579 ISX15 2350, 600hp 2050tq. has MM demandate . I immediately lost 1.5 mpg after demandate was done. Anybody else run into this ? I'm 60 yrs old my driving habits are the same before and after demandate. I've ran it a couple months now thinking maybe it was just me. My fuel avarage before 6.8 to 8.2, now it 4.8 to 6.6 (flatbed) bobtailing went from 10.2 to 8.8 mpgs
(1)My max boost is 38-39 lbs
(2)my highest temp egt 9.5 (I70 west of Denver)
(3)the truck has vibration from 1300-1500 rpms when building boost and allways has.

Demandate truck temps runs tons cooler and has better power. Is it possible the better power is costing me fuel mileage ?

[smorgan87]

Ur boost is way to high for a 2350. Who done tuning?

[smorgan87]

Without tune details id imagine your injection timing is too advanced and turbo tables were fuckered up cpl those things with a high compression engine, high torque and cold air you have urself a very unstable bomb under the hood.

[the missing link]

I am sure if I ran hard ,like 100% or 120km/ hr mine uses more fuel but never running hard as much as possible it uses a lot less
I guess the other thing which won't change things that much is when your pulling hard , keep her above 1500

[Nilao]

Boost tables are way too high. There are copycats out there who claim to do the mm tune but don’t do it properly. At that high of boost your hammering the crank and possibly causing stress fractures in the head not to mention the possibility of burning a hole in a piston.

If it was not done by Mr Haggai, Unilevers or Gearhead you have probably been cheated.

[Rawze]

(01-18-2018 )n2racing Wrote:  I have 2014 peterbuilt 579 ISX15 2350, 600hp 2050tq. has MM demandate . I immediately lost 1.5 mpg after demandate was done. Anybody else run into this ? I'm 60 yrs old my driving habits are the same before and after demandate. I've ran it a couple months now thinking maybe it was just me. My fuel avarage before 6.8 to 8.2, now it 4.8 to 6.6 (flatbed) bobtailing went from 10.2 to 8.8 mpgs
(1)My max boost is 38-39 lbs
(2)my highest temp egt 9.5 (I70 west of Denver)
(3)the truck has vibration from 1300-1500 rpms when building boost and allways has.

Demandate truck temps runs tons cooler and has better power. Is it possible the better power is costing me fuel mileage ?

Anything more than about 32-33 lbs of boost will suck fuel mileage away from that model engine in a hurry. @ 600hp, maybe 34 psi is the upper end on it. - 38+ and no more egr gas IS OVER-BOOSTING and will lead to fuel mileage loss + engine damage.

If you don't want to say publicly who de-mandated it, then PM me with the info and some detail so I can ask them about it if it was someone from this forum.

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