6.4 losing boost and bad fuel mileage

[Ruger5901]

My boss has a 6.4 with DPF delete and spartan tuner. He has it on the lowest hp setting and pulling an enclosed trailer is seeing 8 mpg. I noticed he seems to be losing boost around 70 mph. He can floor it and boost will hold till about 70 mph then you can watch the gauge drop. I thinking the fuel mileage is because of that. Why would you have boost at low mph then lose it at 70? He has the dash daq xl and we do have full scan capabilities. What should I look for?

 

[Dzchey21]

Lower tunes are egt limited. Watch the egts and see if there is s correlation.

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[tbsimmons]

What truck is it? If it is a 450 with 4.88's I can see it.
How much boost is he loosing, 5 psi or 15 psi.
Remember boost is just resistance to flow. Higher RPM, lower boost.

 

[Ruger5901]

It drops from 35 to 15 psi at around 70 mph. I still don't understand how he could be getting 7-8 mpg tuned deleted and towing a Toyota Camry in an enclosed trailer.

 

[Ruger5901]

It's a f250

 

[Dzchey21]

Could also be dropping rail pressure check that to

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[Ruger5901]

What should rail pressure be

 

[Heavyhaul]

24,500psi

 

[Ruger5901]

Thanks bud ill let you know