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Aftermarket fpr adjustment

Dvroofer

Active member
Joined
Jan 23, 2021
Location
Long Beach,ca
I’m running a nuke fprs100 on a nuke rail with a dw300 only using e85. Trying to get a pressure drop issue handled. After running for a distance I drop half a bar fuel psi. Wise sages last night advised me to set it with car not running as I had previously set it with running. I just plugged the vac and set it. My problem is with the rail and a lines I’m losing the pressure after initially priming. I do have a check valve on the feed. Question is should I bypass the relay to the pump to get it set spot on? Only way I can think to have it keep pressure with the car off. Another question is since the cars off and it’s not working at 14..7v as usual would this affect the psi? Sorry if these are dumb questions but trying to get this thing dialed.thanks
 
Hello, I would think that you are correct in setting the FPR when the car is running, as that is dynamic. I can't download their instruction sheet for some reason... Why does it have you plug the vacuum port? My experience is limited to non-boosted applications. Does your system have some form of a return, either in tank or out?
 
Hello, I would think that you are correct in setting the FPR when the car is running, as that is dynamic. I can't download their instruction sheet for some reason... Why does it have you plug the vacuum port? My experience is limited to non-boosted applications. Does your system have some form of a return, either in tank or out?
Yes there’s a 6an return line to the tank. Ig I remember correctly. The instructions had me run the car plug vac then set psi then Reconnect vac. Vac drops the fpr .5 bar
 
that sounds like it is working as intended
My issue is I have it set to 3 bar , with vac that reads 2.5 . I drive 50-70 miles and it shows 2.0 bar with vac . Loosing psi don’t know why. Should be solid at 2.5 with vac which is actually 2.5 unless I’m driving I’d assume
 
Fuel pressure regulators are there to keep a constant differential fuel pressure across the injector. One side of the injector is referenced to manifold pressure, the other side to fuel pressure. The gauges that are typically screwed into aftermarket FPRs measure "gauge pressure" (referenced against atmosphere), NOT the differential pressure the FPR is there to regulate. Aftermarket bourdon tube gauges like that typically fluctuate in what they read depending on atmospheric conditions or how hot they get under the hood. Unless you have other running/drivability issues not mentioned, it sounds to me like the FPR is working as it should.
 
Fuel pressure regulators are there to keep a constant differential fuel pressure across the injector. One side of the injector is referenced to manifold pressure, the other side to fuel pressure. The gauges that are typically screwed into aftermarket FPRs measure "gauge pressure" (referenced against atmosphere), NOT the differential pressure the FPR is there to regulate. Aftermarket bourdon tube gauges like that typically fluctuate in what they read depending on atmospheric conditions or how hot they get under the hood. Unless you have other running/drivability issues not mentioned, it sounds to me like the FPR is working as it should.
Perfect. just making sure . I just started to notice. Zero issues just trying to stay ahead of potential issues. Thank you.
 
Have you confirmed voltage that the pump is getting on startup/ idle vs after driving for 70miles when the pressure is lower.

Both of my cars read the same pressure on startup as after a full day of driving.
 
My drop in fuel pressure from setting off to the end of my drive turned out to be a cheap fuel pressure sensor drifting with engine bay temps.

Diagnosed it by pouring my bottle of water over the sensor mounted in my FPR at the end of my drive, which magically restored my fuel pressure reading.

Ive now swapped to a reputable sensor.
 
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