Nismo FPR = Shitty???

[jspaeth]

Okay....I replaced it with an Aeromotive big boy status, and STILL occasionally have slightly low fuel pressure at idle...

Should be 35-36 psi, sometimes i see 30 psi at idle.

Going to start trying to pinpoint the problem.

Given the quality of Aeromotive, I am leaning towards fuel pump not working perfectly all the time, possibly needing rewiring.

This is the worst problem ever, in my opinion, as a sudden unexpected fp decrease can cause your motor to go byebyes

[steve shadows]

Just use a good stock one. I used one up to 500 whp with track time.

If you want to upgrade get an aeromotive 1:1 Rising rate off-rail.

[UNISA JECS]

What fuel pump are you running by the way? Sounds like a fuel pump going south.

[jspaeth]

I am running a Walbro 255 pump.....I really doubt it's the FPR, as Aeromotive makes top of the line shit, and this happened with BOTH the Nismo FPR and Aeromotive now.....

I would say probably 90% of the time, at idle it reads 36 psi.

The other 10 % of the time it reads 30 psi.


When I BEAT on the car hard, my knock sensor on my PFC is almost always below 20.

Maybe 1 out of every 100 (or maybe even 200) times that I floor it and get full boost and full load, I see the knock sensor go up to 40+.

....and that is with my boost pressure being pefectly controlled with AVCR.

That only leaves inadequate fuel supply (relative to what the map is telling it to feed) as the cause.


1) I need to run my FP gauge into the car to make sure that my FP is going up 1:1 with boost.

2) I need to check voltages at the fuel pump when I see low FP at idle (which is tough, bc it happens so INTERMITTENTLY).


This is just a pain, bc the problem is so intermittent.....I am guessing fuel pump or voltage drop due to wiring.....may try wiring it on it's on power wire or whatever that mod is.

[UNISA JECS]

You know it is possibly that its your tune, its very possibly and highly likely you'll loose a few in/hg (inches of mercury) if yoru to rich or to lean or to much or not enough timing at idle.

Whats the consistancy of you max fuel psi @ max boost psi? Thats whats gonna tell you what the condition of yoru pump is in?

[jspaeth]

Originally Posted by UNISA JECS

You know it is possibly that its your tune, its very possibly and highly likely you'll loose a few in/hg (inches of mercury) if yoru to rich or to lean or to much or not enough timing at idle.

Whats the consistancy of you max fuel psi @ max boost psi? Thats whats gonna tell you what the condition of yoru pump is in?

I do see what you are saying, but I can't see that being the case.

When the FP drops to 30 PSI at idle, the car is idling fine and the vaccum is identical to what it is when it is at 36 psi.

Furthermore, when the FP drops to 30 PSI at idle, I pull off the vacuum line, and the FP gauge reads 39 PSI (again 6 psi too low).

This indicates that the idle/vacuum is NOT the reason the FP is down, but that is an actual supply problem with the pump not giving enough PSI to the FPR (regardless of vacuum).



Yes, you are right, I need to take a look at how the FP is at max boost under full load.

But then 3-5 times EVER that I have had my knock sensor go high (like 40+), I have then pulled over and checked the FP at idle, and sure as shit, it was like 30 or so, rather than 43.

All the other times I do pulls, I have no problems.....again we are talking like <1% of the time that this problem occurs.....


EDIT:

Also, to other people having this problem:

At idle, there is no reason for your FP to go DOWN due to vacuum/idle/etc. problems......if your car is not running right (i.e. not pulling ENOUGH vacuum) or there is a blockage or pressure leak, this will pull LESS vacuum on the FPR and cause your FP to go UP!

Same problems under boost will cause your FP to go down

[om3ga]

Yeah ive been hearing alot of bad things about the Nismo FPR, Ill be going with the tomei or sard unit when i upgrade mine.

[steve shadows]

Yeah I would suggest the stock one or the SARD unit

[Bigsyke]

has anybody measured the PSI of a walbro 255, on a stock FPR? is it nearly the same?

[steve shadows]

Originally Posted by Bigsyke

has anybody measured the PSI of a walbro 255, on a stock FPR? is it nearly the same?

usually its 40-42 psi which is fine if not better. having a tiny bit more FP on injectors under 850 cc size is fine

[UNISA JECS]

Originally Posted by Bigsyke

has anybody measured the PSI of a walbro 255, on a stock FPR? is it nearly the same?

Yea it over runs the stock fuel pressure regulator return system by a good amount ~6-8psi depending the voltage your fuel pump gets (some people gotta shitty wiring and the pump see's less voltage) so results will vary.

[usdm180sx]

I got a sard one for $14.95 at the more-japan.com sale ftw

[Bigsyke]

Well the nismo only fluctuates about 5psi between stops, never gets below 31psi. I would assume this could do for now.

[jspaeth]

If you put the numbers into a calculator.....17 psi boost would give you ~60 psi FP under full boost.

Calculate the fuel flow at 60 psi compared to 55 psi of back pressure, and you find about a 3% reduction in fuel flow.

[cbh148]

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[codyace]

Check the vacuum lines for the FPR to make sure they secure/not ripped. If they are known good, and the FPR has a good strong vacuum signal from the intake, then I'd suspect the FPR.

[hOngsterr]

check the FPR, nismo's leak at the half, mine did that...