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How much pressure in FuelRail while idling? Adj FPR

M.H. Yount said:
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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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.

greenbook said:
the greenbooks say 2,8-3,2 bar on shutted engine and 0,5bar less on idling
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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.
 
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.
 
Canuckvolvo said:
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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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.
 
Linux - not complicating it all. Seems a helluva lot easier to me to fire the car up warm, pull the vacuum hose, hold your thumb over it - and set the pressure compared to jumpering the pump. At best - it's a wash in terms of which procedure is more complicated. Both are simple. However, setting the pressure with the conditions the engine will see when running is a better way to do it. It's not debatable.

But you go on and set it any way you like. I don't mind at all. :)
 
well then do you set it in the winter? or the summer? or perhaps the spring? morning? afternoon? noon? night? starting and re-starting a warm engine is easy, it's starting and restarting cold engines where any magic lies, which would indicate that you'd want the settings most correct then, but what kind of starting are we talking about?
 
How about different fuel blends? Or (oh noes) E85?

Simple fact - the fuel pressure regulator is supposed to maintain a set pressure regardless of all that nonsense.

To repeat myself, if any of that makes any difference in the pressure the FPR holds, then the FRP has problems and needs to be replaced, not carefully recalibrated to match changing conditions.

Speaking of which - I once drove a super nice E28 5 series once. Ran.... very strangely. I looked under the hood and observed a hose clamp on the return line, not holding the hose on, but crimping the line *most* of the way shut. I guess a sort of 'calibrated blockage' method of horribly band-aiding a busted FPR?
 
Bosch_Fuel_Pressure_Regulator_How_it_Works_diagram.jpg


EZ
 
Fun factoid - the donor junkyard motor for my 16V build came from a 94 940T. It was a little grungy, had 240K miles, but wasn't really wrecked (few dings on the side). It was a bit sooty in the cylinders. One time I tried the FPR to see if it worked better than the one I was using, and fuel shot out of the manifold air line.

So as far as i can tell, the FPR broke, started flooding the motor with gas, and they just promptly sold it to a junkyard instead of investing $40 in a new FPR (or however much they cost). I guess the diagnostic fee would have been more than the car was worth?
 
linuxman51 said:
well then do you set it in the winter? or the summer? or perhaps the spring? morning? afternoon? noon? night? starting and re-starting a warm engine is easy, it's starting and restarting cold engines where any magic lies, which would indicate that you'd want the settings most correct then, but what kind of starting are we talking about?
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Your questions, theoretically if not practically, all apply no matter which method you use to set it. So, since jumpering the pump is so uncomplicated -- feel free to go ahead and reset each time you drive the car. ;-)
 
M.H. Yount said:
Your questions, theoretically if not practically, all apply no matter which method you use to set it. So, since jumpering the pump is so uncomplicated -- feel free to go ahead and reset each time you drive the car. ;-)
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well according to your advice, the best way to do it would be to set it cold, then re-set it warm, maybe check it cruising down the road, and again when you stop.
 
M.H. Yount said:
Your questions, theoretically if not practically, all apply no matter which method you use to set it. So, since jumpering the pump is so uncomplicated -- feel free to go ahead and reset each time you drive the car. ;-)
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The only way that they really apply for a proper FPR is in the change of elasticity of the spring, which changes ever so slightly due to temperature fluctuations from norm.
 
Surprised this thread hasnt been locked up yet, all this tyranny over somethin so simple? Next thing you know, its gonna end up turning into the best way to pump gas in your car. C'mon people, if you have a factory standard fpr, bolt the damn thing on, if its adjustable, set to your hearts desire and adjust accordingly ( hence the reason why its called an adjustable fpr). When i go to shut my door, where is the best place to grab and pull?
 
aaron740gl said:
Surprised this thread hasnt been locked up yet, all this tyranny over somethin so simple? Next thing you know, its gonna end up turning into the best way to pump gas in your car. C'mon people, if you have a factory standard fpr, bolt the damn thing on, if its adjustable, set to your hearts desire and adjust accordingly ( hence the reason why its called an adjustable fpr). When i go to shut my door, where is the best place to grab and pull?
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I dont know why there is so much trolling about this... if you adjust your fuelpressure 0.5 bars high, you have an errorscale of 20% which the LH has to adapt.. but adapting errors is ****ty when going performance.. so why not adjust the fuelpressure to that value which is it desired to be and preclude "errors" or better inadequatenesses in the end?

So.. as everyone said.. the fuelpressure has to be 3bar no way around..

The question is... set that when idling with hose connected or not... thats the question which came up when my buddy told me to run 3bar in idle with hose connected which would be 4bar with 0.5bar of boost...

i tried that yesterday and it was running ****ty with that setting, so i went back to 2,5bar in idle (hose connected) and it runs better...



thx guys... maybe i have to speak with my buddy again.. im absolutely unconvinced about his theory.. he works alot with whiteblocks.. and their FPR is higher in the basesetting i believe so maybe theres an error in reasoning with him? dont know...


i will get back to you when we have wiped this.. ;)
 
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