Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Johnny English]

Not too long ago my fuel pump played up not totally though so was able to provide some press in the pipe. Although it was not enough to start my car but absolutely enough for me to be sure in my truth that the pump is OK  so I decided to install a fuel press gauge just in case. I've got a problem though  I don't know correct pressure values, which are needed during the process of calibration. After using "search" option got general informations only : 3bar (or 3,7 ? ) at idle and closed throttle. I need two values : at idle and 6k RPM.
Any info much appreciated   

THX     

[Kevin Wood]

Fuel pressure is constant, not RPM related.

2.5/3.0 V6s are 3 BAR, 2.6 and 3.2 are 3.7 BAR if I recall correctly.

[Johnny English]

Thanks , Kevin ! 
I thought it depends on the RPM that's why a vaccum pipe connected to fuel press regulator : various RPM  - various power of sucking - various fuel pressure...seemed to be logical. What is the role of vaccum though ?

[Webby the Bear]

oil pressure is RPM relevant. fuel pressure constant 

[Abiton]

I thought fuel pressure in the rail was regulated to be a constant pressure relative to intake manifold pressure. This way the pressure difference across the injectors is constant, and fuel delivered per unit time predictable.

So it will be lower at idle than at WOT.
 

[Andy H]

I thought fuel pressure in the rail was regulated to be a constant pressure relative to intake manifold pressure. This way the pressure difference across the injectors is constant, and fuel delivered per unit time predictable.

So it will be lower at idle than at WOT.
 

You would think so........

but the pressure pipe goes to a tapping on the underside of the throttle bodies so who knows what that does to your fuel pressure when you press the throttle

[Abiton]

I thought fuel pressure in the rail was regulated to be a constant pressure relative to intake manifold pressure. This way the pressure difference across the injectors is constant, and fuel delivered per unit time predictable.

So it will be lower at idle than at WOT.
 

You would think so........

but the pressure pipe goes to a tapping on the underside of the throttle bodies so who knows what that does to your fuel pressure when you press the throttle

Upstream or downstream of the butterflies?

[2woody]

Fuel pressure is constant, not RPM related.

2.5/3.0 V6s are 3 BAR, 2.6 and 3.2 are 3.7 BAR above manifold pressure

[Kevin Wood]

Fuel pressure is constant, not RPM related.

2.5/3.0 V6s are 3 BAR, 2.6 and 3.2 are 3.7 BAR above manifold pressure

The FPR is referenced to atmospheric pressure on the 2.6 / 3.2. Can't recall whether it's the same on a 2.5/3.0.

[aaronjb]

oil pressure is RPM relevant. fuel pressure constant 

Not always But you probably haven't encountered RR FPRs yet in your course (On the Omega you're right, though, as Kev & 2woody have already said)

[Johnny English]

After all I didn't need to calibrate it's occurred by itself. The meter shows 2.8bar at starting and 2.2 - 2.3bar in normal mode. Today I'll have a brief trip then more experience later. 

[Kevin Wood]

Hmm. Thinking about this some more, the FPR reference comes from the inlet hose to the ICV on a non-DBW V6, so it's not vaccum referenced either. So, you should be seeing 3.0 BAR all the time. Your measurements sound low on that basis.

[Marks DTM Calib]

The one occasion I measured it the fuel pressure was 3.0 bar on the money on a 3.0 (you are correct on the pressures for 2.5/3.0 and 2.6/3.2 Kevin).

The reference feed is pre throttle and I suspect is simply a convenient connection post filter to stop crap and crudd getting in.

Certainly when sucking on the vac feed to the reg whilst monitoring rail pressure the variation was not great (read 0.1-0.2 bar)

[Johnny English]

Don't think more on correct values I'm sure all of you right !  I needed a virtual preference that helps me to decide whether pump works or not. I got it so everythink is OK the gauge itself anyway seems proper one the differ between value said above and shown one can be caused by an air bubblie as I couldn't find any vent hole on sensor...    Thx guys ! 

[Kevin Wood]

Don't think more on correct values I'm sure all of you right !  I needed a virtual preference that helps me to decide whether pump works or not. I got it so everythink is OK the gauge itself anyway seems proper one the differ between value said above and shown one can be caused by an air bubblie as I couldn't find any vent hole on sensor...    Thx guys ! 

On the contrary, if the pump is not working efficiently, low fuel pressure, lessening under demand when the engine is running, is what I'd expect to see as a symptom. An air bubble won't affect the reading on the gauge. It will be compressed a little but the gauge will still slow the correct pressure.