Fuel pressure question

[livingez_123]

08 Denali with fresh engine, new everything. I've started tuning the new build and noticed that my fuel pressure starts out at 58-60 on a cold start and when the engine temp hits 100° it drops down to 42-45psi. I replaced the pump module with a new Bosch unit and the pressure is the same. Do these use a PWM pump? If so that explains why it drops. I've looked everywhere and I can't find a definitive answer.
The Denali runs great so I'm inclined to just move on with the tune.

 

[B-train]

Yes, they are a PWM controlled pump. Eliminated the need for a return fuel line and pressure regulator.

 

[livingez_123]

Yes, they are a PWM controlled pump. Eliminated the need for a return fuel line and pressure regulator.

Thanks, that explains it.

 

[5StarCustmSolutns]

Thanks, that explains it.

Spent so much time looking for technical answers like this. Found HP Tuners forums to be very helpful

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