Fuel Reg function?

[BIGRED]

I found the vacuum line to the fuel regulator had a hole and is sucking air.

How does the reg work? - Meaning with vacuum applied VS released, what does it do?

Thanks
Don

[Ross]

The vacuum signal is indicative of engine load. Under load the vacuum signal drops, increasing fuel pressure. The volume of fuel delivered is determined by the time the injector is open and the pressure it is delivered at. The computer determines the open time of the nozzles.

[BIGRED]

So if all vacuum is lost when the engine shuts...could that cause the fuel to drain back out of the rail?

I am trying to solve an intermittent fuel supply problem.

Thanks
Don

[Ross]

Vacuum opens it, returning fuel to the tank. A loss of vacuum would increase pressure. I've heard of people disconnecting it to fatten up the mixture, don't know if it works but it seems plausible.
It's not the sort of device that is likely to be intermittant either.

[Bill R.]

Vacum changes the pressure at which it opens to return fuel to the tank.





Vacuum opens it, returning fuel to the tank. A loss of vacuum would increase pressure. I've heard of people disconnecting it to fatten up the mixture, don't know if it works but it seems plausible.
It's not the sort of device that is likely to be intermittant either.

[BIGRED]

Maybe I blew-out my check-valve?

As I understand it.... no vacuum = more pressure in the rail....full vacuum less pressure in the rail.

My vacuum hose has a rip in it....My symptom is hard starting after shutting down for any length of time.

[gale]

Hard starting after shutdown is more often a sign of a leaking fuel pump check valve. If the pressure bleeds off while it's still warm, it can cause vapor lock-like symptoms (not actually vapor locked, but takes extended cranking time to restart). BMW has a check valve "kit" which was a retro-fit for the e38, 16 14 9 068 988, or just about any automotive parts place should have one which you can splice in-line with the fuel line near the filter.

[bill g]

The purpose of the fuel pressure regulator is to maintain a constant difference between pressure in the fuel rail and the manifold pressure. The injection system relies on this being constant because the amount of fuel being injected for various speeds and load conditions is varied by the ECU solely by changing the length of time the injectors are open.
To put it very simply if there was no fuel pressure regulator then under conditions of high vacuum in the manifold such as at idle fuel will tend to be sucked through the injectors when they open and the fuel/air mixture would be over rich.
If the vacuum hose is leaking your regulator will not be working properly, causing the mixture at idle and low throttle openings to be too rich, although the ECU may be able to adjust or compensate for this to some extent. However the engine will not be running right.

Bill G

[BIGRED]

Thanks for the additional clarification. I replaced the line without the expectation of it helping (hot/hard start issue discussed in a different post), but stranger things have happened.

It seemed that there was a much greater throttle response and gobs more power. BUT .... I had been driving our turbo diesel earlier in the day and....lol.
I would assume an increase in mileage if it does.

Because I live up in the mountains, I wanted to avoid a trip into the city for fuel pressure diagnostic tools, but guess that's where I am heading.

Leaning towards a fuel check valve issue, but I want to make sure the pump is operating within specs before I dig into it for the 3rd time.

Thank you
Don

[BIGRED]

While I check on the fuel pressures in the system, I thought i would say...

What a difference replacing that stupid (hidden) cracked vacuum hose to the fuel pressure regulator made.

1. At a stop light you don't know the motor is running (by feel).

2. 1/2 second hesitation the first 1/2" of pedal gone.

3.The mileage shot up. I reset the computer while on the highway. At 55 to 60 it was reporting low to mid 30's at 65 to 70 upper 20's. My guess is the average for our kind of driving will go to the mid 20's from the upper teens.

4. General power (seat of the pants) seems to be up a fair amount.

[Ferret]

I thought that one of the other functions of the pressure regulator was to stop the pressure surges associated with suddenly slamming the throttle closed at high RPMs?

Iirc it's possible to build up a lot of momentum in the fuel rail on a big engine and cause seal problems when the injectors suddenly stop after a high RPM run...