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Old 06-13-2012, 04:44 AM   #1
MadDog_945
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Default How much pressure in FuelRail while idling? Adj FPR

Yesterday i was told something i heard the first time.. from a guy who certainly knows what hes talking about...


So.. i bought this knockoff aeromotive FPR.. how to setup pressure?

My thinking was: i have a factory 3bar one.. so start engine and put it to 3bar minus intakepressure (about -0.55barVAC) so it should be 2,54bar in idle... but i was told its wrong..


It should have 3 bar in idle...?? A little world broke together for me when i was told this?
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Old 06-13-2012, 05:23 AM   #2
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3 bar at idle with vac on the fuel pressure regulator.
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Old 06-13-2012, 05:26 AM   #3
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ah.. OK..


the greenbooks say 2,8-3,2 bar on shutted engine and 0,5bar less on idling... this is strange...
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Old 06-13-2012, 07:54 AM   #4
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that's probably about right. with the vacuum line hooked up, it drops fuel pressure at idle. with no vacuum line hooked up, it should sit right around 3bar (or ~ 44psi +-).
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Old 06-13-2012, 08:12 AM   #5
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3 bar with vacuum hose to fuel pressure regulator disconnected and plugged. This is what I read it should be.
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Old 06-13-2012, 09:06 AM   #6
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Quote:
Originally Posted by lummert View Post
3 bar with vacuum hose to fuel pressure regulator disconnected and plugged
wat?!
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Old 06-13-2012, 09:09 AM   #7
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wat?!
Plugged to the manifold. Oterwais it is air leak
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Old 06-13-2012, 09:50 AM   #8
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So its running engine -> unplug hose -> set to 3bar -> done ?


thats what i did.. but thats wrong... in a way? meh.. im confused now...
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Old 06-13-2012, 10:25 AM   #9
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So its running engine -> unplug hose -> set to 3bar -> done ?


thats what i did.. but thats wrong... in a way? meh.. im confused now...
Why is that wrong? your fuel pressure should be 3 bar without vacuum on a stock setup.
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Old 06-13-2012, 11:30 AM   #10
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So its running engine -> unplug hose -> set to 3bar -> done ?


thats what i did.. but thats wrong... in a way? meh.. im confused now...
no thats not wrong. The pressure regulator compensates for vac/boost. in the case of a LH 2.4 Volvo the fuel pressure difference over an injector is 3 bar in stock form. with 1 bar boost the fuel rail will be at 4 bar. at heavy engine braking and close to .8 bar vacuum the fuel pressure will be 2.2 bar. That is, when set at 3 bar with the vacuum hose connected.
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Old 06-13-2012, 11:33 AM   #11
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Get the engine to a warm idle; unplug the vacuum line from the regulator and cover the end with your thumb or a piece of tape; set your fuel pressure to 3.0 bar (gauge) +/- 0.2 bar; then hook the vacuum line back up and it should drop down into the 2.5 bar range (a bit higher if you have an aftermarket cam that reduces vacuum at idle). That's what everyone and the greenbook is saying -- except for triebwerk.
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Old 06-13-2012, 11:53 AM   #12
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Get the engine to a warm idle; unplug the vacuum line from the regulator and cover the end with your thumb or a piece of tape; set your fuel pressure to 3.0 bar (gauge) +/- 0.2 bar; then hook the vacuum line back up and it should drop down into the 2.5 bar range (a bit higher if you have an aftermarket cam that reduces vacuum at idle). That's what everyone and the greenbook is saying -- except for triebwerk.
This is what I was going to suggest^
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Old 06-13-2012, 01:29 PM   #13
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why your all tripping hard. The engine does not need to be running plugged or warmed up to set fuel pressure.

All you need is to have the fuel pump running. then set it and leave it alone.
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Old 06-13-2012, 02:22 PM   #14
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why your all tripping hard. The engine does not need to be running plugged or warmed up to set fuel pressure.

All you need is to have the fuel pump running. then set it and leave it alone.
The fuel pressure needs to be checked both with the vacuum hose connected to and disconnected from the fuel pressure regulator.
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Old 06-13-2012, 02:30 PM   #15
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the engine does not need to be running to set base fuel pressure with a regulator.
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Old 06-13-2012, 02:58 PM   #16
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the engine does not need to be running to set base fuel pressure with a regulator.
This is correct, just need a jumper wire for the pump relay socket.
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Old 06-13-2012, 04:40 PM   #17
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You need to check it with vacuum on once you've set it guys; so you might as well set it under the conditions it will see when it's running. And while it may not generate a big difference, the regulator is going to behave a bit differently at 200F than it will at 80F.

You don't have to have the engine running to set base timing either -- but if you've got a timing light, you're better off using it to set the timing with the car running. Same deal with fuel pressure. You don't have to have it running -- but it's a better standard procedure.
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Old 06-14-2012, 11:12 AM   #18
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my experience is this, i bought a bosch adjustable fpr designed to run on the Buick Grand National, i had to turn the pressure way down, it sits at maybe 1.5 bar at idle, just about 20 psi, i'm running 36lb pontiac GTP V6 injectors and tlao chips, car comes up on boost fine and fuel pressure increases accordingly and the car speeds along at 11:1 a/f, the computer will compensate the pulse of the injectors to attain the correct a/f ratio, i'm makin 205hp 237lb/tq so no worries if you're running lh 2.4
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Old 06-14-2012, 11:17 AM   #19
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He's not.
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Old 06-14-2012, 11:26 AM   #20
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Pump(s) probably make a bit more pressure at ~14V then they do at ~12V I would think, so probably *most accurate* to set everything with the car running, no?
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Old 06-14-2012, 11:31 AM   #21
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Quote:
Originally Posted by M.H. Yount View Post
You need to check it with vacuum on once you've set it guys; so you might as well set it under the conditions it will see when it's running. And while it may not generate a big difference, the regulator is going to behave a bit differently at 200F than it will at 80F.

You don't have to have the engine running to set base timing either -- but if you've got a timing light, you're better off using it to set the timing with the car running. Same deal with fuel pressure. You don't have to have it running -- but it's a better standard procedure.
what? the stock system runs a 3 bar pressure regulator, which is 3 bar with no input on the vacuum diaphragm. It doesn't matter if the engine is running or not with the vacuum unhooked, it should be 3 bar.

Quote:
Originally Posted by greenbook
the greenbooks say 2,8-3,2 bar on shutted engine and 0,5bar less on idling
The only thing you're looking for with it running and hooked up is that the pressure is lower than the base 3 bar setting.

Why are you complicating this procedure? this is nothing like setting ignition timing with the engine off (the closest thing it is to timing would be akin to locking out any ignition advance while the car is idling and setting base timing there. your other suggestion might as well read "well you need to set base timing at 3500 rpms since that's where the car will be most of the time" derrrrp).

even if the underhood temps are 200 degrees it is completely folly to even think that the fuel temperature is anywhere near that, and additionally a 1-2psi fluctuation in fuel pressure is going to manifest itself as...

drumroll please.....


nothing because it will see that much variation just in engine vacuum pulses.

in reality, with a 2.4 system the fine details don't matter much anyway. +- probably .5 bar, the car will behave the same after about a minute or two.


This is a simple procedure. Jump the fuel pumps with the engine off and set it to 3 bar, and be done. The only other thing that may need attention is if the fpr has an adjustable ramp (2:1 fuel pressure vs input pressure). Most inexpensive ones do not, so you set the base pressure, hook the vacuum line up, and move on to something else.
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Old 06-14-2012, 11:33 AM   #22
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He's not.
actually... he is. check the build thread.
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Old 06-14-2012, 11:37 AM   #23
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Incidentally, if we're going to follow this other train of thought, you should install your spare tire while the vehicle is cruising at 55mph, since that's about where it'll be used most often.
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Old 06-14-2012, 12:02 PM   #24
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Quote:
Originally Posted by Canuckvolvo View Post
Pump(s) probably make a bit more pressure at ~14V then they do at ~12V I would think, so probably *most accurate* to set everything with the car running, no?
The fuel pressure regulator's entire job is to provide the correct fuel pressure (relative to manifold pressure). Regardless of what the fuel pump is doing (it should always be pumping too much - otherwise you need a better fuel pump). And regardless of what the engine is doing, sipping at idle, or guzzling at full boost.

If the FPR regulates at a higher pressure because the fuel pump bumped up its output a little at 14V instead of 12.5V, then the FPR is likely not working up to snuff, and should be replaced.
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Old 06-14-2012, 12:06 PM   #25
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Wha....
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