hey, i finally installed my defi gauges and found that my fuel pressure isnt as gradual as i expected it to be. it stays at 40psi till i hit boost. . . then, RIGHT when i hit boost, it hammers its way to 60psi. does that sound right? ive never seen one work so i dunno. i have the feed adjustable FPR. its a bolt on piece.

paul

 

Assuming it is a 1:1 FPR it should should add 1psi of fuel pressure for ever psi of boost. If you have a rising rate regulator it the increase in fuel pressure will be greater than 1lb for every psi of boost. I have a 1:1 Sx regulator. When I roll into the boost it increases pressure gradually with no sharp jumps.

Is it at 40 when the car is at zero vacuum and zero boost, or 40 at idle (at which point the motor is operating in vacuum)? 40psi at idle will be around 47 at 0psi. If you're boosting to 13psi immediately, and it's set to 40psi at idle, 60 seems reasonable.

 

Paul:

Are you running an aftermarket pump?

Sonny

 

yes, im running the supra pump.

see, i cant find documentation of what its rate is. i was "told" that its 1:1. it stays at 40psi till i hit boost. . . nothing changes UNTIL i hit boost. . . meaning. . . anything over 0psi. . . . but i also have to kinda get on it for it to get up there. the car isnt tuned very well right now and the duty cycle for the wastegate is waaaaaaaay low. . .

thanks,
paul

 

The stock FPR is definitely 1:1. I tested it when I did my fuel system overhaul. With 20" of vacuum (equivalent to -10 psi), I saw about 34 psi of fuel pressure. At atmospheric pressure (0 psi), I saw 44psi. When I pressurized the FPR with 10 psi (using a hand pump), the fuel pressure went up to 54 psi.

The vacuum/boost hose going to the top of the FPR is accessible under the lift point on the back of the engine. You might wanna unhook it there and then use a hand pump to test it.

Sonny

 

At idle look at the pressure. Then disconnect the hose to the fpr(while still running) and the pressure should rise. I see my pressure move with my throttle. Meaning very small changes in the pedal translate to small pressure changes.

I had a bad fpr and this is what it did - it would show no variation of fuel pressure with throttle until the pump kicked into high mode (like 2500 rpm) and then it would spike up to a much higher pressure and then the pressure would decrease from there as the car built boost and rpms.

The hose test at the top will tell you if your fpr is having problems - if the pressure doesnt change at all at idle with the vacuum hose removed it is likely you r frp is bad.

Mine was a paxton and died after 2-3K. Paxton did not warranty it or offer a rebuild kit but were happy to try and sell me another one. I went to summit and got the aeromotive for about $140 and it has been great.

BTW it shouldnt matter what pump you have - the fpr is designed to control fuel pressure versus vacuum/boost. The only case where it would matter is if the pump doesnt give enough or too much pressure. (which would not give the symptoms you are having).

Shawn
www.3rdgenrx7.com

 

shawn, good information. . . i wanna go ahead and say again that i have the FEED adjustable FPR. . . not the stocker. ill do that test later when i get my idler pulley fixed. . . aluminum EVERYWHERE. HAHAHAHA.

paul