fuel pressure regulator

[steve-in-ga]

I am familiar with how fuel pressure regulators work with a vacuum hose connected. But, it is my understanding that my '04 TB uses a fuel pressure regulator with no vacuum on the vacuum hose that connects it to the resinator. There is no vacuum present on mine also. Just trying to make sure this is correct.

Will someone explain in laymans terms how this FPR works without vacuum present on the vacuum line.

 

[kickass audio]

Actually there is vacuum on that little hose. With your intake anything that is before the throttle body has negative vacuum, after the throttle body is positive vacuum. So with the more you open your throttle body the more suction you have in the resonator and in the FPR vacuum line. With the throttle being closed you are not drawing as much vacuum on the FPR.

With the FPR if you have little to no vacuum then your FPR will remain closed. This is what happens if you are at idle or very low engine speeds. When you give it more gas your throttle body opens up more and draws more vacuum. That extra draw in vacuum will cause the FPR to open up through the suction and then allow the fuel to recirculate at the fuel rail and also drop your fuel pressure down a little while it is open.

Now for me I think it is weird that our FPR is set so that at wide open throttle the FPR is open, thus meaning you have a lower fuel pressure on the fuel rail that goes to your injectors. You would think that for WOT you would want to have more fuel pressure.

 

[bobdec]

If that vacuum port is on the intake it's just the opposite. Highest vacuum is at idle or deceleration with TB blade closed. As TB opens vacuum drops actually to the point of no vacuum (100 Kpa) at WOT. If perfect 100% of air required by the cylinders is being supplied through the TB opening and therefor there is no vacuum built up. This is where blowers or turbos (boost) comes into play to actually induce positive pressure in the intake to move more air into the cylinders.. To test a vac controlled regulator you pull the vac line off the regulator (no vacuum) and the fuel pressure should go up 5-7 lbs.

For vehicles w/o vacuum controlled regulators the software/tune in the PCM/ECM will compensate for the lower pressure caused by high volume fuel demands. It will adjust the injector pulse width (keep them open longer) to hold the injector lbs per hour delivery constant.

 

[kickass audio]

Oh man I was wrong about the pressure. oops. sorry for the mis-information

 

[steve-in-ga]

So, are you saying that my '04 TB with inline 6 should have vacuum at the port on the resinator at idle? Mine does not.

 

[Texan]

I have never checked mine, but it may be minimal at idle. Check it at higher RPM's.

 

[AtlWrk]

So, are you saying that my '04 TB with inline 6 should have vacuum at the port on the resinator at idle? Mine does not.

No. These are "atmospheric" regulated FPRs. That port on resonator chamber is between filter and the throttle plate and does NOT see manifold vacuum (past the throttle plate). This type of regulator only adjusts fuel pressure based on ambient pressure and has nothing to do with throttle position. This is different than the commonly thought of vacuum modulated system that adjust fuel pressure based on intake manifold pressure.

This PDF explains in a bit more detail:
http://www.autoshop101.com/forms/h42.pdf

 

[steve-in-ga]

Thanks, that pdf helps a lot.

 

[Ruben F Quingalahua]

No. These are "atmospheric" regulated FPRs. That port on resonator chamber is between filter and the throttle plate and does NOT see manifold vacuum (past the throttle plate). This type of regulator only adjusts fuel pressure based on ambient pressure and has nothing to do with throttle position. This is different than the commonly thought of vacuum modulated system that adjust fuel pressure based on intake manifold pressure.

This PDF explains in a bit more detail:
http://www.autoshop101.com/forms/h42.pdf

Hi. So that little hose connects to the resonator. Plastic box.? That has no vacuum

 

[Isshman Garcia]

Just in case people still come here in 2021 for answers..The FPR has NO vacuum to the hose connected to the resonator. If you go to the Service Manual or even Mitchell1DIY($20 a year) and go to "Fuel System Diagnosis" and read the diag step7 - it clearly states...disconnect the "Vent" hose... NOT VACUUM- Atmospheric. Its also refered to as the "Fuel Pressure Regulator Atmospheric Vent" So fuel pressure is most certainly tied to the MAP sensor readings..as well as any other sensors that are tied to the atmosphere. Hope this helps.