frustrating fuel pressure issue

[GTSBoy]

Colour me confused. How can you remove the dampener to see what the idle pressure is? I feel that you are confusing the wording or the physical location of these devices. The dampeners are upstream (and perhaps on) the rail. The reg is at the outlet of the rail and is the very last physical device in the fuel system other than the return line to the tank.

Do us a favour. Locate the real, actual pressure reg. Remove the vac line from it and tell us the idling fuel pressure then.

[damnonrs]

13 minutes ago, GTSBoy said:

Colour me confused. How can you remove the dampener to see what the idle pressure is? I feel that you are confusing the wording or the physical location of these devices. The dampeners are upstream (and perhaps on) the rail. The reg is at the outlet of the rail and is the very last physical device in the fuel system other than the return line to the tank.

Do us a favour. Locate the real, actual pressure reg. Remove the vac line from it and tell us the idling fuel pressure then.

Dampener is after the fuel pressure regulator on the rb26, removing the vac line changes the idling by like 0.05 bar or something like that 

If it satisfies you I also ran the car with the hose right off the fuel pressure regulator as stated and nothing changed

[Ben C34]

On 12/10/2022 at 6:54 PM, damnonrs said:

Dampener is after the fuel pressure regulator on the rb26, removing the vac line changes the idling by like 0.05 bar or something like that 

If it satisfies you I also ran the car with the hose right off the fuel pressure regulator as stated and nothing changed

The dampener would do nothing if after the regulator. What would it dampen?

 

Taking the vac line off the reg at idle MUST show an increase in pressure. That's how referenced regulators work mate. If it's not doing that it isn't working.

Or you have the vac source plumbed wrong. Can you feel a suction on the vac line when disconnected at idle?

[joshuaho96]

1 minute ago, Ben C34 said:

The dampener would do nothing if after the regulator. What would it dampen?

 

Taking the vac line off the reg at idle MUST show an increase in pressure. That's how referenced regulators work mate. If it's not doing that it isn't working.

Or you have the vac source plumbed wrong. Can you feel a suction on the vac line when disconnected at idle?

Isn't the stock RB26 fuel damper in the return line? That's how I read it here:

[damnonrs]

3 minutes ago, joshuaho96 said:

Isn't the stock RB26 fuel damper in the return line? That's how I read it here:

Yea that’s exactly it, and yes the fuel pressure goes up like I said earlier when I remove the vac line 

[BK]

4 minutes ago, joshuaho96 said:

Isn't the stock RB26 fuel damper in the return line? That's how I read it here:

Yes, does f**k all

[BK]

9 minutes ago, Ben C34 said:

The dampener would do nothing if after the regulator. What would it dampen?

Nothing, useless, But is in the return

[joshuaho96]

7 minutes ago, damnonrs said:

Dampener is after the fuel pressure regulator on the rb26, removing the vac line changes the idling by like 0.05 bar or something like that 

If it satisfies you I also ran the car with the hose right off the fuel pressure regulator as stated and nothing changed

I agree that something is wrong if pulling the vac line only changes the fuel pressure by 0.05 bar. Look at your manifold pressure in absolute pressure. If your idle is -20 inHg then assuming your base pressure is 4 bar it should drop to 3.32 bar with the vacuum line plugged in. Are you sure your vacuum line is plugged in at the front of the balance tube? I have heard of people mixing up the charcoal canister vacuum line for the FPR vacuum line.

[damnonrs]

5 minutes ago, joshuaho96 said:

I agree that something is wrong if pulling the vac line only changes the fuel pressure by 0.05 bar. Look at your manifold pressure in absolute pressure. If your idle is -20 inHg then assuming your base pressure is 4 bar it should drop to 3.32 bar with the vacuum line plugged in. Are you sure your vacuum line is plugged in at the front of the balance tube? I have heard of people mixing up the charcoal canister vacuum line for the FPR vacuum line.

It’s plumbed like this

[joshuaho96]

5 minutes ago, damnonrs said:

It’s plumbed like this

That's the correct port, not sure why your fuel pressure is behaving weirdly then. You sure it only changed by 0.05 bar and not 0.5 bar?

[damnonrs]

2 minutes ago, joshuaho96 said:

That's the correct port, not sure why your fuel pressure is behaving weirdly then. You sure it only changed by 0.05 bar and not 0.5 bar?

I will check again tomorrow, could I have a pretty bad vacuum leak somewhere in the surge tank or something 

[GTSBoy]

1 minute ago, damnonrs said:

could I have a pretty bad vacuum leak somewhere in the surge tank or something

No. Is there a strong vacuum signal on that vac line on the pressure reg when you pull it off? If there is not, suspect the source. If there is, then suspect the reg. But something is defo f**ked.

[BK]

4 hours ago, joshuaho96 said:

That's the correct port, not sure why your fuel pressure is behaving weirdly then. You sure it only changed by 0.05 bar and not 0.5 bar?

Change in real world is generally 3 - 4psi. 40 psi at idle full vacuum, 43psi at 0 vacuum with line pulled. Bar talk at this level is silly. 0.5bar change I would not expect realistically, that's a bit dramatic of a change at 7.5 psi and 0.05bar is basically no change.

[joshuaho96]

12 hours ago, BK said:

Change in real world is generally 3 - 4psi. 40 psi at idle full vacuum, 43psi at 0 vacuum with line pulled. Bar talk at this level is silly. 0.5bar change I would not expect realistically, that's a bit dramatic of a change at 7.5 psi and 0.05bar is basically no change.

I was just going by the book value mentioned earlier. Wouldn't this depend on the particular slope/response of the fuel pressure regulator? I figure the goal at idle is to drop fuel pressure so you stay deeper in the linear regime of the injectors.

[Murray_Calavera]

When I upgraded to a radium FPR, with the vacuum line pulled, base pressure is 43.5 psi. With the vacuum line back on, the pressure drops to 33.5 psi. 

Big difference between the stock FPR and the radium one for sure. 

[joshuaho96]

21 hours ago, damnonrs said:

So I dove into the fuel system today, 

I removed the line coming out of the damper and plugged it into a fuel canister. The idling pressure dropped from 4.25 idling to 4.05 steady. I’m assuming the 5% improvement is because of all the twists and turns tk get back to the fuel tank. So damper isn’t the problem. But then I also tried plugging it straight from the regulator and it was the same thing. All that’s left to test now is regulator itself or the rail… which brings me to: do I buy a radium fuel rail with damper and fuel pressure regulator in one? Also check this out. When I rev the car the pressure just goes to 3.5 and jumps back to 4.2 I posted a video 

IMG_7513.MOV 72.15 MB · 1 download  

 

I'm not an expert on fuel systems but a 0.2 bar drop in fuel pressure just from the return lines not flowing enough sounds like a lot, especially if you haven't bypassed the FPCM. Have you bypassed the FPCM btw?

[BK]

32 minutes ago, Murray_Calavera said:

When I upgraded to a radium FPR, with the vacuum line pulled, base pressure is 43.5 psi. With the vacuum line back on, the pressure drops to 33.5 psi. 

Big difference between the stock FPR and the radium one for sure. 

What size fuel lines ?

What pump ?

[Murray_Calavera]

18 minutes ago, BK said:

What size fuel lines ?

What pump ?

Lines are stock sized.

Pump is Walbro/Aeroflow/TI automotive 525 LPH.

[damnonrs]

46 minutes ago, joshuaho96 said:

I'm not an expert on fuel systems but a 0.2 bar drop in fuel pressure just from the return lines not flowing enough sounds like a lot, especially if you haven't bypassed the FPCM. Have you bypassed the FPCM btw?

What’s a fpcm?

this is what the fuel pressure does plugging it in and out. It raises when you unplug it

 

 

[BK]

38 minutes ago, Murray_Calavera said:

Lines are stock sized.

Pump is Walbro/Aeroflow/TI automotive 525 LPH.

Though so, 10psi change is not normal and sounds very restricted. What possessed you use one of these on stock lines ?!

For example our white 32 has the same 525lph with AN8 top hat fittings, AN8 supply and return lines with an FPR1200 using PWM.

Changes about 4 - 5 psi

Stock Nismo pump  stock reg on 5/16 lines changes about 3-4psi in my 33.