how much should my fp change with line off?

[christians87]

when i remove the vacuum line on the top of my fuel pressure regulator the fuel pressure usually only goes up like bearly 2psi. is that normal or should it go up more than that. also, it takes it a little while for the fuel psi to rise once i take the line off. shouldnt it rise as soon as i take the line off? thanks.

 

[toofastforyou]

It should go up 10 psi...

Claude. :smile:

 

[Blown&Injected]

I have always seen between 6 and 8 psi change with several different regulators.

 

[Nasty Wendy]

There is no standard number for that on a modified engine. Every different cam grind will idle with a different amount of vacuum. If you install a vacuum gauge you'd know exactly what you should see. If you idle @ 16" of vacuum that is -7.86psi ... roughly 8psi of fuel pressure increase you should see. Figure every 2" of vacuum to be 1psi of fuel pressure rise you should see when the line is removed.

 

[turbojd]

I have always seen between 6 and 8 psi change with several different regulators.

Me too, mine goes from 36 with the line on, to 43 with the vacuum line off.

 

[Blown&Injected]

There is no standard number for that on a modified engine. Every different cam grind will idle with a different amount of vacuum. If you install a vacuum gauge you'd know exactly what you should see. If you idle @ 16" of vacuum that is -7.86psi ... roughly 8psi of fuel pressure increase you should see. Figure every 2" of vacuum to be 1psi of fuel pressure rise you should see when the line is removed.

Well that would explain the change in my FPR...

Wendy: You have some peculiar remarks in your profile...looks like you have found a different and creative parts store

 

[christians87]

is my fpr bad?

so does that mean that my fpr is bad sence it only rises 2 psi?

 

[Blown&Injected]

might be some other problem like a broken or plugged vacuum line

 

[87GN_70GS]

Get an air pressure source, like a hand-held pump, etc and put air pressure on the regulator. The fuel pressure should match any increase in air pressure. You can also get a hand-held vacuum pump and repeat the test.

 

[turbojd]

I use a hand held mityvac.

 

[christians87]

thanks for all the input. ill probly use the hand held vac pump to see if it changes. i dont think the vaccum line is plugged because when i pull it off it makes a pretty loud hissing noise and the engine idles rougher because of the vaccum leak.

 

[turbojd]

Maybe it's your fuel pressure guage? What guage do you have on the fuel rail.

 

[christians87]

i have the fuel rail mounted fp gauge from g body parts. it cant be bad. its only like 2 months old.

 

[turbojd]

Does your fuel pressure rise 1 lb. with every 1 lb. of boost. You could also check out the return line for any kinks, or a vacuum hose leaking at one end. Maybe possible faulty regulator?

 

[christians87]

I dont know if the fuel pressure rises with the boost because i cant see the gauge when im under boost. But, I do know that when im under boost the scan master never realy reads lean. Also, everytime I start the car after the fuel pressure has dropped, it takes a few moments for the fuel pressure to rise up to its normal pressure at idle. The car has its original fuel pump.

 

[turbojd]

I would run a mechanical fuel pressure guage up to the windshield to see if the fuel pressure rises with boost. Could be a weak pump, what regulator are you running ?

 

[bmackinnon]

I dont know if the fuel pressure rises with the boost because i cant see the gauge when im under boost. But, I do know that when im under boost the scan master never realy reads lean. Also, everytime I start the car after the fuel pressure has dropped, it takes a few moments for the fuel pressure to rise up to its normal pressure at idle. The car has its original fuel pump.

The factory pumps were barely adequate for a bone stock car when brand new.... I would say after 77k, you should replace it immediately, symptoms or not.... and you need to add a hose to your fp gage, and tape it to the windshield so you can see the fp under operating conditions and verify it rises 1:1 with boost.... failure to do both of these is just begging for disaster....

Edit: YIKES!! Especially with your mods/boost level!!!

 

[christians87]

Well not currently. Right now my car is realy messing up lol. When I go to spool the turbo and build boost the car will start to have compressure surge realy bad and then the car will usually begin to break down. The whole time the scanmaster is reading rich, usually 810 mv or higher, and it will not build over 7 psi boost. in hopes of trying to narrow down the sorce I have removed the boost controler and alky. so im now back at stock boost, my street chip in the ecu, and no alky. i can not figure out what is wrong. Im going to try taking off the intake pipe to see how free the turbine wheel spins. what do you guys think is wrong?

 

[bmackinnon]

Well, it's not compressor surge with the stock turbo under those conditions... I would suspect, in order, bad maf, bad coil pack/ign. module, or equally suspect, fuel pump.... even though you are showing 810 mV on the SM, it is slow as hell, and can't display the instantaneous O2's like directscan or powerlogger can... it is only giving about 1 frame of data every 1.5 seconds... vs. high speed data, 20 frames/second... car could be dying lean and recovering (causing the compressor to snort and fart and make all kinds of racket), all under the SM's nose.....

also you never stated 'it's normal pressure'..... what is the base fp, and what chip? Verification of the fuel pressure/rise-ratio is MANDATORY.... even more so with your initial worry about only a 2 psi rise line off, and slow at that.... :wink:

 

[RobS]

Im going to try taking off the intake pipe to see how free the turbine wheel spins.

When you check the turbine, Check the bearing play on the turbo. Try moving the wheel in and out. It should have no play when you do this. Also see if the fins are bent like the wheel has hit the side of the housing.