2xLS1

iTrader: (25)

I've had this on the truck forum all day with no replies. I'm sure someone here knows the answer.
Educate me on the vacuum refrenced fuel pressure regulator used on the trucks. I'm used to dealing with F-body fuel systems with the in tank regulator. I'm interested in how the fuel rail pressure changes under high vacuum vs low vacuum and what happens when boost pressure is applied to the vacuum source on the regulator when running a blower.

DrX

iTrader: (6)

Injector flow rate is proportional to the difference between the fuel rail pressure and the manifold pressure. A boost/vacuum refereced FPR adjusts fuel pressure to keep this differential constant thereby maintaining a constant injector flow rate. In a non boost referenced system the only way to compensate for the changing flow rate is for the PCM to increase/decrease the injector duty cycle accordingly. This is addressed in the tune.

For example, under boost conditions, non referenced systems will have to keep the injectors open more of the time as boost increases(higher duty cycles) to compensate for reduced flow. The same size injectors will be maxed out sooner in this type of system than in a referenced system.

This is one reason why I am converting to a boost referenced return style system.

2xLS1

iTrader: (25)

Thanks for posting. I'm familiar with the IFR tables and how they differ in both f-body and truck calibrations. I guess what I'm looking for are real world examples of what the fuel pressure at the rail actually does under the different conditions. For example can anyone tell me like with a high vacuum signal at the FP regulator you will see 58 psi and with a low vacuum signal at WOT you will see 61 psi. Is that how it works? I'm only using those values as examples. And then, what happens to the fuel pressure when the regulator sees a boost signal like when you add a blower to a truck that the FP regulator is not really designed for or expects to see.

DrX

iTrader: (6)

I believe that the FPRs on the trucks that have them on the rail will respond to boost. Seems to be around 1:1 This was discontinued with the introduction of the returnless systems in 2004. The non referenced FPR is now in the tank again.

http://www.performancetrucks.net/for...ght=referenced

2xLS1

iTrader: (25)

Thanks for that link. That's the info I was looking for.