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Old 12-20-2013, 11:11 PM   #1
1MOFOSTI
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Default Walbro 255L, Fuel Pressure SOLVED!

EJ207 JDM/AUS, 04 STi / FPRed @21 PSI / 90% IDC / DW1000cc / 55ft / 83mm MAF /3in inltet / walbro 255 / rails etc...


Ive been trying to figure out what is happening with the fuel press. There is no leaks anywhere i have triple checked.

What happens is, start the car ,255l walbro primes / cold start = 3.2bar (46PSI) / Warm idle = 2.7bar (39PSI) / WOT = 3.8bar (55PSI) i know these are all lower than normal but am stumped why?

Fuel Pressure SOLVED! see post #9

-1MOFO
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Last edited by 1MOFOSTI; 12-28-2013 at 11:08 PM.
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Old 12-21-2013, 03:12 AM   #2
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Bump for the 4 PSI of pressure i'm missing.
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Old 12-21-2013, 04:58 AM   #3
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i'd say it's your fuel pressure reg/ecu/fuel relay rather than the pump. the pump itself doesn't control how long it remains on for.

tried a different pump to make sure it's not faulty? process of elimination...
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Old 12-21-2013, 06:50 AM   #4
ride5000
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what does the fuel rail pressure read with the FPR manifold reference disconnected?
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Old 12-21-2013, 09:44 AM   #5
1MOFOSTI
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Quote:
Originally Posted by vicious_fishes View Post
i'd say it's your fuel pressure reg/ecu/fuel relay rather than the pump. the pump itself doesn't control how long it remains on for.

tried a different pump to make sure it's not faulty? process of elimination...
The pump is tested and working 100%. I'm 90% sure the ECU isn't the cause as the tuner was confused as to why we are slightly under base pressure as a result tuned 90% IDC @ only 21PSI .

Whats the best way to test the relay and is there a way that i can test the FPR's while its on the car? Im running twin OEM FPR per rail setup, (at the end of each billet rail sits a OEM FPR.)

I also disconnected the relay so that there is no pressure and reconnected it to see if it builds up properly but still reads 4 PSI under base.


Quote:
Originally Posted by ride5000 View Post
what does the fuel rail pressure read with the FPR manifold reference disconnected?

Do you mean disconnect the manifold reference vac lines to each FPR (as im running the twin setup) and read what pressure it's getting?

Last edited by 1MOFOSTI; 12-21-2013 at 10:07 AM.
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Old 12-21-2013, 02:06 PM   #6
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Quote:
Originally Posted by 1MOFOSTI View Post

Do you mean disconnect the manifold reference vac lines to each FPR (as im running the twin setup) and read what pressure it's getting?
You can disconnect the reference line, but you don't NEED to. Turn the ignition on, but don't crank the car. The pump comes on for a few seconds to prime the fuel system. At this point in time, the pressure in the manifold is at atmosphere, so will give the same results as disconnecting the reference line.

If your pump is hard-wired, you can simulate this by letting it run for 5-10 secs, then pulling the fuse.

What does fuel pressure do? How fast does it decay after prime (should bump up to ~43-44 psi and take a long time to decay. Barely noticeable decay unless you go away and come back 30+ minutes later.)
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Old 12-22-2013, 12:10 AM   #7
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Quote:
Originally Posted by Concillian View Post
You can disconnect the reference line, but you don't NEED to. Turn the ignition on, but don't crank the car. The pump comes on for a few seconds to prime the fuel system. At this point in time, the pressure in the manifold is at atmosphere, so will give the same results as disconnecting the reference line.

If your pump is hard-wired, you can simulate this by letting it run for 5-10 secs, then pulling the fuse.

What does fuel pressure do? How fast does it decay after prime (should bump up to ~43-44 psi and take a long time to decay. Barely noticeable decay unless you go away and come back 30+ minutes later.)

Just tested see below:

- Ignition on / fuel pump prime = 3.3 BAR ( 47.8 PSI )
- Once its stopped priming = 2.9 -3.0BAR ( 42 - 43.5 PSI )

It holds 42-43PSI for 1min
From there every 3 - 4mins it drops - 2PSI
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Old 12-23-2013, 03:13 AM   #8
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Someone must have see this before?
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Old 12-28-2013, 11:45 AM   #9
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Guys problem solved.

I was under the impression that it had to be 43.5 PSI or above with the manifold pressure reference connected. Turns out it's with it disconnected and here's my test results. (i actually have more than i need lol.)

Vac disconnected from FPR : 3.3BAR ( 47.8 PSI )
Vac connected to FPR : 2.7 ( 39PSI )
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Old 12-28-2013, 01:05 PM   #10
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ahhh. yes always set base pressure with atmospheric. best outcome possible really!
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Old 12-28-2013, 10:05 PM   #11
1MOFOSTI
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Quote:
Originally Posted by vicious_fishes View Post
ahhh. yes always set base pressure with atmospheric. best outcome possible really!
^^ + 1000 , very happy it was my lack of knowledge and not the car
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