Vacuum at FPR?

[Maverickxeo]

Just another odd question from me!

On my 04 4.2L Envoy, I noticed that the fuel pressure regulator does NOT actually have a vacuum source on it. The line that connects from the regulator to the intake resonator does NOT show vacuum (I don't believe it would as it is before the throttle body). It was my general understanding that a fuel pressure regulator relied on vacuum to control fuel pressure when the engine is idling. Am I missing something here?

 

[Mooseman]

I have seen other systems, including the one on my FI snowmobile, that the regulator is just a hose vented to atmosphere. I think it just goes by atmospheric pressure rather than vacuum. On these trucks, I think that hose to the resonator is so that if the regulator fails and leaks, it will go into the resonator, evaporate and get burned off.

 

[Maverickxeo]

I have seen other systems, including the one on my FI snowmobile, that the regulator is just a hose vented to atmosphere. I think it just goes by atmospheric pressure rather than vacuum. On these trucks, I think that hose to the resonator is so that if the regulator fails and leaks, it will go into the resonator, evaporate and get burned off.

Ah interesting. So then is fuel pressure just static then?

 

[Mektek]

On a GM 3.1 the pressure goes from 40 at idle to 45 when revved.

hose to the resonator is so that if the regulator fails and leaks, it will go into the resonator, evaporate and get burned off.

I wonder what the engineers were thinking when they designed the regulator........

 

[gmcman]

I want to speculate the hose is if the air intake gets too restricted, then it will begin to supply vacuum and lower the fuel pressure?

 

[Mooseman]

It's all speculation on my part as to the actual function of that hose.

 

[Redbeard]

I had an '04 4.2 and it didn't have any vacuum on that port either. . I wonder if they just wanted it vented to "cleaner" air. For 16 years it didn't make sense to me either.

 

[gmcman]

There won't be any vacuum on that port since that plenum is part of the air intake from the filter.

Only way to draw a vacuum is if the air filter was almost totally clogged.