fuel pressuge gauge install after or before stock reg?

[a73_4g67]

Hi,

Ive installed a T fitting with pressure gauge(0 to 100psi) between the fuel rail and fuel filter.
I'm getting high readings at idle. Its around 47-50psi with vacuum on and close to 60psi with vacuum off.

Car is all stock, stock fuel reg. GVR4. I doubt it if the fuel reg was changed.

Should I install it after the rail? Looking at those gauges with AFPR, they're mounted on the reg. That means its after the fuel reg right? So should I T after the return line?

 

[steve]

It's the pressure before the regulator that's important.
In the case of regulator mounted gauges, the gauge port is before the regulator valve.

Since your pressure changes with the reference port vacuum I verify the gauge is reading correctly first.

Steve

 

[a73_4g67]

Thanks for the reply Steve.

Now I understand. So is it ok that I cut the fuel hose into 2 and inserted the brass T fitting with gauge between the fuel rail and fuel filter? Will this cause some discrepancy in reading than the one mounted at the rail or at the reg? Im 20psi off the normal reading. Car is all stock including pump. What kind of reading should I expect when racing/reving the engine(no load)? Should pressure drop a bit and goes back to the original reading?
If theres boost, it should rise to 1:1 pressure to boost right?

It's the pressure before the regulator that's important.
In the case of regulator mounted gauges, the gauge port is before the regulator valve.

Since your pressure changes with the reference port vacuum I verify the gauge is reading correctly first.

Steve

 

[c4uldr0n]

By the sounds of it, you installed the gauge properly. If you have a stock regulator and the pressure is that high, it is odd. What does the gauge read of the car is off or disconnected? Do you notice that the car is running rich (black smoke out the tail pipe)?

 

[a73_4g67]

I'll try to check on the reading after the car is shut off. I remember its around 20psi. If vacuum is disconnected, it will be higher by around 10psi.
The reason I installed this gauge is because Im having problems boosting past 10psi.
at 10psi, it runs great and revs smoothly to redline. 2.5 dp and 3" exhaust. But when I turn the boost up to 14-15psi, it sputters at 4k rpm. So that time Im guessing its either Im running rich or starving from fuel. At idle it doesnt give off black smoke. I need to let someone check when the car is under boost.

By the sounds of it, you installed the gauge properly. If you have a stock regulator and the pressure is that high, it is odd. What does the gauge read of the car is off or disconnected? Do you notice that the car is running rich (black smoke out the tail pipe)?

 

[steve]

What kind of reading should I expect when racing/reving the engine(no load)? Should pressure drop a bit and goes back to the original reading?
If theres boost, it should rise to 1:1 pressure to boost right?

The fuel pressure should always be equal to base pressure (psi) + reference pressure (psi).
So under vacuum your reference pressure is negative and winds up reducing the fuel pressure where under boost the reference is positive and increases the fuel pressure.
Also remember that the typical boost gauge measurement for vacuum is inches of mercury and 2 inhg is about 1 psi.

Steve

 

[a73_4g67]

Ive found the problem. Its the FPR.
I removed the return hose from the FPR, start the engine. Theres no fuel coming out from the fpr. I replaced it with a surplus unit. Now it reads 37-39psi at idle, vacuum off. 30-31psi, vacuum on. I took it out for a test drive. Turn up the boost controller. It runs smooth at 15psi. Car feels so much stronger. No wonder my plugs are always wet with gas and color black. Thanks for all your replies.

The fuel pressure should always be equal to base pressure (psi) + reference pressure (psi).
So under vacuum your reference pressure is negative and winds up reducing the fuel pressure where under boost the reference is positive and increases the fuel pressure.
Also remember that the typical boost gauge measurement for vacuum is inches of mercury and 2 inhg is about 1 psi.

Steve