what to set fuel pressure at?

98COBRA281 · Oct 12, 2009

what psi do i set my fuel pressure regulator to? isnt stock like 44psi?....

:SNSign:

trinity_gt · Oct 12, 2009

98COBRA281 said:
what psi do i set my fuel pressure regulator to? isnt stock like 44psi?....

:SNSign:

The injectors are designed to operate across a nominal pressure drop of ~39-psi. At idle, if your engine is pulling say 18-inHg of vacuum so the idle fuel pressure should be set to about 34- or 35-psi or so. With the engine off, the pressure should rise to ~39psi.

98COBRA281 · Oct 12, 2009

so with the engine off, and the key on, i should set it at 39psi?

trinity_gt · Oct 13, 2009

98COBRA281 said:
so with the engine off, and the key on, i should set it at 39psi?

Yes.

98blackstallion · Oct 13, 2009

is that with the vacuum line on or off?

trinity_gt · Oct 13, 2009

98blackstallion said:
is that with the vacuum line on or off?

If the engine's not running, it doesn't make a difference. If the FP is to be set with the engine running, it can be done one of two ways:

1) Disconnect the vacuum line and expose the FPR to atmosphere. Set the FP to 39psi. Re-connect vacuum line.

2) Leave vacuum line connected and use vacuum or MAP gauge to determine manifold pressure at idle. If you know the inHg (inches of mercury) pulled at idle, you can roughly determine manifold pressure with:

Code:

MAP ~= (29.92-Vac)*0.491154

So if you're pulling 18inHg on a vacuum gauge, there'd be ~(29.92-18)*0.491154 or ~5.86psia in the intake manifold. Subtract this number from 39 to get the value you want to set the FP to (in this case, 39-5.86=33.1psi).

It's probably easier just to pull the vacuum line and set it to 39psi. :|

98COBRA281 · Oct 13, 2009

98blackstallion said:
is that with the vacuum line on or off?

how do you like you edelbrock intake? your the only other person that i have seen that has one.......

98COBRA281 · Oct 14, 2009

i dont know if 39psi is enought?

i set it at 39 with the vac line off, and is breaking up really bad under acceleration with load, and it has terrible throttle responce, i dont know if it matters, but the car does have a walbro 255 pump, 24lb injectors, and was dyno tuned on the stock fuel pressure setting.......

trinity_gt · Oct 15, 2009

98COBRA281 said:
i dont know if 39psi is enought?

i set it at 39 with the vac line off, and is breaking up really bad under acceleration with load, and it has terrible throttle responce, i dont know if it matters, but the car does have a walbro 255 pump, 24lb injectors, and was dyno tuned on the stock fuel pressure setting.......

Can you leave the gauge connected and drive around a bit (carefully) with it to see what the FP is doing under other driving conditions? Are they FRPP injectors? And, silly question, but you're setting it to 39-psig, not 39-psia, right?

98COBRA281 · Oct 15, 2009

trinity_gt said:
Can you leave the gauge connected and drive around a bit (carefully) with it to see what the FP is doing under other driving conditions? Are they FRPP injectors? And, silly question, but you're setting it to 39-psig, not 39-psia, right?

i am leaving the gauge on all the time, they are denso injectors, and i have a autometer gauge that i set it to 39.......

trinity_gt · Oct 15, 2009

98COBRA281 said:
i am leaving the gauge on all the time, they are denso injectors, and i have a autometer gauge that i set it to 39.......

So what does the gauge show during driving, especially when the car is acting up?

What does it read at idle? At WOT? At part-throttle?

98COBRA281 · Oct 15, 2009

trinity_gt said:
So what does the gauge show during driving, especially when the car is acting up?

What does it read at idle? At WOT? At part-throttle?

i cant see it while driving, it mounted to the FPR under the hood, but at idle i want to say it dropes to about 30ish and when i rev it it never goes back up to 39, it bobbles aroung 35ish or less..............

what to set fuel pressure at?

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