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Base Fuel Pressure For Nismo 555cc Inj's

SATO GTS

By SATO GTS,
in Engines & Forced Induction

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SATO GTS Community Regular

SATO GTS

Posted
Posted

recently tried to install some nismo 555cc inj's into a rb25 with a standard fuel pressure reg that was running about 50 pounds at idle with vacuum connected .

with the vacuum disconnected it bumped up to 65 pound . the problem is the with the duty and latency correction carried out i was unable to get a stable 14.7:1 mixture at idle , but just free revving it was all good. carried out initialization of the power fc and started again the best mixture reading i was able to acheive was 12:1 which is just way to rich at idle.

std inj's went back in and load std map and all was good .

had the inj's flowed to check flow rate and pattern but the asnu inj machine was unable to supply enough fluid to get a correct reading but with the pressure it was at the inj's flowed exactually the same . we even cleaned two inj's and reflowed them but made no difference.

I am starting to think that either there is to much fuel pressure at idle and the power fc cant correct the inj at that position and load of the map due to too muck pressure and flow or i have a faulty pfc.

I have a peirburg (a german brand ) fuel pump .

the inj's are the correct resistance and they are receiving the correct voltages .

What base fuel pressure's have other ppl set this size inj up at?

GeeTR Grand Master

GeeTR

Posted
Posted (edited)
What base fuel pressure's have other ppl set this size inj up at?

Most set em up, at factory pressure; 42-43psi base.

Your FPR could be broken. Check return line to tank is ok.

Replace with another known good one, as a test.

Edited by GeeTR
The Mafia Grand Master

The Mafia

Posted
Posted
that is the question that i want a answer for .

but no idea .

I have a nismo adjustable reg on order to see it i can correct the base pressure .

are you gonig to try and make any more than 350rwkw? If not then throw the FPR in the bin and re-fit the factory item.

These threads are by the dozen "Why doesn't my FPR work" - answer is because they are crap and are not needed for lower power figures.

I have tuned so many cars, and seen crap AFRs, going up and down, all over the place. Fit the factory Item and back to normal.

saliya Rising Star

saliya

Posted
Posted
are you gonig to try and make any more than 350rwkw? If not then throw the FPR in the bin and re-fit the factory item.

These threads are by the dozen "Why doesn't my FPR work" - answer is because they are crap and are not needed for lower power figures.

I have tuned so many cars, and seen crap AFRs, going up and down, all over the place. Fit the factory Item and back to normal.

My reading of the original post is that the adjustable FPR is going to be used to

combat too-high fuel pressures that exist on a system with a stock regulator:

that is, the OP thinks the original regulator may be broken...

Regards,

Saliya

saliya Rising Star

saliya

Posted
Posted
Why doesn't anyone think the gauge might be crap?

Hey,

The gauge may well be crap and I'd definitely be checking

it against something that was known-good because the

change-back-to-stock fixes the problem. Use the gauge while

there is no problem ... if it's still reading 65psi, it's probably

broken.

If I had to guess at a problem based only on the information in

the OP I'd say recheck the latencies and correction factors.

BUT, my point was that using an adjustable FPR to adjust fuel

pressure for testing seems fair enough to me. I don't believe

that they're inherently evil :action-smiley-069:

Regards,

Saliya

SATO GTS Community Regular

SATO GTS

Posted
  • Author
Posted (edited)

thats right the stock FPR is running at 50-65 psi .

the fuel pressure gauge is brand new but again i will use a good known gauge to check aswell as checking the return to make sure its not blocked

i will be installing a adjustable FPR to bring the pressure down to 40psi to see if i can get a correct idle mixture .

is that high pressure to much for the larger nismo 555cc inj's to run at idle but ok with stock inj's?

I trimed the injs back to 66% and tried 50% still to rich.

Edited by SATO GTS
The Mafia Grand Master

The Mafia

Posted
Posted

I'm using Nismo 555cc injectors, with a powerfc, Nismo 275lph@72psi Fuel pump, and my corrections are set at 77%.

If your factory regulator is feeding them 55psi+ at idle, then your return is blocked, or your factory FPR is fooked.

They are pretty easy to diagnose. Guilt-Toy has given some good advice.

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