Fuel pressure with vac line on....

[cecil bass]

Can someone remind me what the fuel pressure should be set at with the vacuum line connected......
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[Heisenberg]

42-45
give or take

 

[cecil bass]

42-45
give or take

And from there it should rise 1 psi per psi of boost right?

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[Sweet6]

With vacuum connected probably 35 to 40

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[Sweet6]

Vacuum off 42ish

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[earlbrown]

It will drop from the base setting differently for each car.

With the line on it's 'base setting -vacuum' It's not exact, but 2"HG of vacuum is very close to 1#.

 

[cecil bass]

The way i can tell if i have a delivery issue is if my fp doesn't rise with boost right?

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[Heisenberg]

My bad - I misread - vacuum line "CONNECTED"

Start the engine with the vacuum line disconnected from the fuel pressure regulator port.

Using a 3/16 size allen wrench and a 7/16 wrench, tighten the allen screw until the fuel pressure rises to the desired level.
CAUTION: DO THIS SLOWLY!
Clockwise raises the fuel pressure and counter-clockwise drops the fuel pressure.
Next, tighten the lock nut securely and re-connect the vacuum line.
Fuel pressure should drop about 10psi with the vacuum line in place.

RECOMMENDATIONS:
*ET: 15 seconds to 13.5 seconds - 42psi at idle no vacuum, 13.5 to 12.5 – 45psi at idle no vacuum,
12.5 times & faster – 47 to 50psi MAX at idle no vacuum.
(Settings are only recommendations for starting point.
Each car is different and must be dialed in.)
*Under boost conditions, the fuel pressure regulator should provide about 1 additional psi for each pound of boost.
For example, a car set at 45psi running 20lbs of boost equates to 65psi, provided you have a sufficient fuel delivery (fuel pump) in the tank.

 

[Heisenberg]

The way i can tell if i have a delivery issue is if my fp doesn't rise with boost right?

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Or a variety of other misc issues - such as vacuum line leaks, FPR diaphram problem ,etc etc.
But if all else is ok - then it will give you a good indication of the FP's ability to keep up with flow requirements.

 

[Heisenberg]

So the point is:
Make sure you can set your base at 42-45 with the vacuum line OFF
THEN- reconnect the vacuum line and see if it drops the appropriate amount.
Tighten everything.
Then do your blasts and watch the FP gauge on your window - or wherever.

And oh - don't get lazy and not tie wrap those vacuum lines back tightly.
You'll regret that.

 

[earlbrown]

The way i can tell if i have a delivery issue is if my fp doesn't rise with boost right?

Correct. Take your base setting with the line off. Add that to how much boost you're running. The gauge reading needs to be exactly the sum of the two numbers, base+boost.

 

[EYE-OPENER]

Hold on...so 2 questions...
1. There should be a significant drop in fuel pressure when line is hooked back up?
2. Faster cars should have higher baseline FP? I have always read 43# with
One off.

My fuel pressure is about the same with line on or off. Not sure what would cause that, and honestly the car runs great and rises 1:1 and has the twin pumps. I have never seen the needing higher Baseline pressure....somebody please help me out here...

 

[Chuck Leeper]

Hold on...so 2 questions...
1. There should be a significant drop in fuel pressure when line is hooked back up?
2. Faster cars should have higher baseline FP? I have always read 43# with
One off.

My fuel pressure is about the same with line on or off. Not sure what would cause that, and honestly the car runs great and rises 1:1 and has the twin pumps. I have never seen the needing higher Baseline pressure....somebody please help me out here...

1. Don't look for the 10psi drop that's been mentioned, as gospel. Could be 3, could be 7... Haven't seen 10.
2. Faster car has nothing to do w/ the base psi. [Assuming the injs are correctly sized for the FWHP], The injs are flowed at a particular psi. [usually 3 bar]. That info is then incorporated into the tune. Fuel delivery is then calculated using that number.
3. If the fp on your car does not drop w/ the addition of the vac, then there's a problem:
Could be the regulator.
Could be the gauge.
Could be the vac source. [IE: a leaky line, etc.]
A. Are the twin pumps running all the time?
B. Is the system plumbed w/ the stock lines? If the answer to "A" is yes, then you may be overrunning the return line. The way I check is to see if I can raise and drop the fp at least 5psi.

 

[EYE-OPENER]

I am seeing 6 lbs...so sounds like I'm good there...I thought the same thing with fuel pressure...no sense in boosting pressure if the rest of the system is supposed to handle the increase in boost. Secondary pump is on a Hobbs switch.

 

[cecil bass]

Thanks, i now have a better understanding of what's going on.
Don't know what i would do without you guys!!!!
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[EYE-OPENER]

Couldn't agree more