Where To Tap for Fuel Pressure Signal & What To Set FPR At?

[rico05]

I assume on the return line, but just making sure. Thanks guys! I need to get this gauge on so I can dial in my Nismo FPR. Also, what is a good starting place for FP to be? I am about to have a EGT so I can tune it as we go, but what is a good baseline to be at for about 11psi and a T25G?

[81na ZX]

42.5psi WITHOUT any vac adjustment. ie without any vac lines hooked up.

Generally you put the gauge tap as close to the FPR as possible. Aftermarket FPR's have a gauge port on them That brass plug is the gauge port.

[rico05]

Like I said, I have a Nismo one. No plug for the pressure source here. On which line? Feed or return?

[WeldingHank]

feed. return has almost no pressure.

and you cannot use EGT for fuel tuning. your EGTs barley change with A/F ratio. they change with ignition timing.

[biosehnsucht]

42.5? where did you get that?

the FSM says "The pressure regulator maintains the fuel pressure at 240.1 kPa (2.501 bar, 2.55 kg/cm^2, 36.3 psi).", I would take this to mean regulated relative to the intake manifold vacuum/boost naturally..

So what I did to set it easily, unhook vacuum line to FPR, put car to 'on' and jumpered the relay socket for the fuel pump to make it stay on, and adjusted until it was at 51psi (36.3 + 14.7).

[boost_boy]

42.5psi WITHOUT any vac adjustment. ie without any vac lines hooked up.

Generally you put the gauge tap as close to the FPR as possible. Aftermarket FPR's have a gauge port on them That brass plug is the gauge port.

Woh , This is waaay too much fuel pressure for those stock injectors. The engine's idle will tell you this as well. Fuel should be regulated at about what "biosehnsucht" said........35-37psi.

Dee

[rico05]

So just tap into the line from the filter to the regulator and go from there as the FSM says. Is that 35-37 psi w/ or without the vac line hooked up to the regulator?

[c-rad]

Woh , This is waaay too much fuel pressure for those stock injectors. The engine's idle will tell you this as well. Fuel should be regulated at about what "biosehnsucht" said........35-37psi.

Dee

Right, but he said 42 with the vac line NOT hooked up. With it hooked up the pressure should decrease to about 37 at idle under 18-20" Hg.

[81na ZX]

Exactly Cause you can't get an accurate setting with a vac hooked up every time (baro pressure, atsmosphere, etc)Fuel injectors are rated at 42.5psi.

[biosehnsucht]

Hrm, from what the FSM implies it should be set to 51 at ambient pressure (36.3 + 14.7) but you're saying 42.5 ... I assume you've set it thisway yourself and haven't leaned out yet? I mean my car runs better at 51 than wtf it was before but it's still only making something like 20mpg average it's turning out..

[rico05]

F'ing GREAT. I get it all hooked up, start the car. At 20 in/Hg fuel pressure was dead on at 34 PSI. W/ no Vac source, it was just shy of 43 PSI. So....looks like my issue is not my FPR. ANyone wanna buy a brand new Nismo FPR still in the Nissan box?

[Nunook]

how much?

just installed my FPgauge and it says like 27 at idle (20vacuum)?i think the gauge is ***ked. oh well!

[rico05]

Dunno. Like I said, it is brand new in the Nissan box. I paid about $135 shipped for it (maybe a few more, it was ~$130 + shipping)

[float_6969]

I will on monday, but we'd have to work on the price. I found it for cheaper online. Shoot me an email and we'll talk. [email protected]

[biosehnsucht]

keep in mind most you see online are going to be SR/KA ones which bolt up but you have to loop the return line around like I did in order to get it to work as it comes off at the wrong angle off the FPR. So a real CA one might well be worth the extra $$$ if you don't want to deal with that..

[float_6969]

He never mentioned that it was a REAL CA NISMO FPR. If it is and the angle is correct, then I would be intrested in it for that price. I didn't know that NISMO made one for the CA, so I just assumed that it was an SR/KA one.

[biosehnsucht]

I *think* they made a real one. But half their **** is no longer listed on their website, so I don't ever bother looking for an official part#.

ANYWAYS, so I've been reading mixed information on fuel pressures here and on SXOC .. what should I set the FPR to? From the FSM (36.3 relative to manifold) sounds like it should be 36.3+14.7 as I've said or 51, but others have said 42.5 (which sounds like 43.4 or whatever the KA/SR are regulating relative to the manifold), but I've seen #'s mentioned anywhere from 36 to 41 mainly.

[rico05]

No, this is a SR/KA/VG/RB one that I have.

[float_6969]

I'm reading 36.3 also. That's what I'd set it at.

[biosehnsucht]

as in, 36.3 relative to ambient? or relative to manifold? I hope ambient, cause then I'd be suddenly getting a whole lot more mpg once I adjusted it to that, but I wouldn't want to adjust to that when thats too low (=lean)

[float_6969]

If you think about it, it HAS to be ambient. The whole point of the regualor is to change the pressure in the fuel rail relative to the CHANGES (in relation to ambient) in the manifold. So you would base it off of ambient, then when you reference it to the manifold, it will change the pressure in the fuel rail to compensate for the changes in vac/pres in the manifold so that you get a consistant amount of fuel from the injectors. That way all the computer has to do is vary the duration of the injector opening to change the amount of fuel being injected into the motor. Does that make sense?

[rico05]

So is my 35 PSI ok? Or should I keep the Nismo FPR and bump it up a little? I mean, my issue is that I am running ungodly rich, so I think keeping the FPR is really not going to help me.

[biosehnsucht]

makes sense.

35psi is a bit low, rico, but is that really what your stock one is doing? You have an upgraded pump right?Even with mine set way too high (51 haha, I'll fix it tomarrow) it's running less rich than the walbro 255 lph high pressure pump and stock FPR did..

[rico05]

Yeah. Stock FPR and a Walbro 255lph pump. Still for sale then

[float_6969]

I was gonna get it from you till those HKS cams went up on eBay. I've been after a set of them for months and I don't want to let them go. If you've still got it in a couple of weeks I'd still like one, but those cams are more important right now...

[rico05]

It's all good man. I shouldn't have a problem getting rid of it.

[biosehnsucht]

Set it to 37psi now, runs much better.

at first it could barely idle, since the ECU had learned to try and lean out as much as it can all the time now it was barely injecting any fuel at the correct pressure, once the o2 heated up it idled fine, much smoother

hopefully this will get more than 20mpg now

fyi at idle it was pulling about 29~30 or so psi at IDLE with it set to 37~38 w/ no vacuum connected. which is about right.. see this SXOC post ... I don't know what manual he found the specs in that it specified vac attatched and unattatched, but whatever. I set it ~1 psi too high since setting it to exactly 36.3 is impossible and more is safer

rico: was your 35psi w/ or w/o the vacuum line atttached.. if it was without it was slightly low, if it was with it was ~5psi too high (not beyond the ECU's abilites to correct in closed loop (? i think it is) mode, but will make you run somewhat rich otherwise)