I have a b&m gauge and fpr, my fuel psi drops under load.....it holds for alittle bit and the drops I am curious of what this could be

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 4gencivicef9 &raquo;</TD></TR><TR><TD CLASS="quote">I have a b&m gauge and fpr, my fuel psi drops under load.....it holds for alittle bit and the drops I am curious of what this could be </TD></TR></TABLE>

When you're reading the gauge, the vacuum line from the fuel pressure regulator to the intake manifold has to be unplugged. If it's not unplugged the engine will draw a vacuum on the regulator and throw your reading off.

So when you checked the gauge, was the vacuum line pulled off?

Usually I unplug it from the IM (so it's just dangling from the FPR), then put my finger over the nipple on the IM so your intake doesn't suck air in and your idle doesn't serge.

Your fuel pressure shouldn't move at all. Should be constant, though you can only read it correctly if the FPR vacuum line isn't connected.

 

yes the vaccum line was hooked up. So thats what I am doing wrong.
another question

I am running a gsr what should the fpr be set at with vaccum off,,,, also I am running d15 injectors from the original motor....

 

What year?

If it's '98-'01 GSR or ITR it's supposed to be between 47-54psi static (with the vacuum hose disconnected).

Like I said before, put your finger over the nipple on the intake manifold so your idle doesn't go nuts.

 

92 hatch civic

 

your fuel pressure will drop a little under a load, but should correct itself quickly, if it doesnt your pump is weak or you have a restriction in the feed (possibly dirty filter). most likely though weak pump.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Syndacate &raquo;</TD></TR><TR><TD CLASS="quote">When you're reading the gauge, the vacuum line from the fuel pressure regulator to the intake manifold has to be unplugged. If it's not unplugged the engine will draw a vacuum on the regulator and throw your reading off.</TD></TR></TABLE>

WTF?!

The fpr has a vacuum reference line so that it can increase fuel pressure as load increases. That way pressure can be low at idle for driveability. If you pull off that line, the fuel pressure will just stay static except for the pressure drop of the injectors spraying the fuel. I see no problem with wanting to watch the pressure change with vacuum. It's not throwing anything off. That is your actual pressure changing with load.

schardbody has your answer.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by schardbody &raquo;</TD></TR><TR><TD CLASS="quote">your pump is weak or you have a restriction in the feed (possibly dirty filter).</TD></TR></TABLE>

 

Your close. When at idle with 18+inhg. the gas gets pulled from the injectors so lower pressure is needed when idling.

When off idle there is not as much vacuum pulling the gas through the injectors so the fuel pressure is increased. Not really increased but normal pressure.

 

What you're trying to say isn't very clear to me. You sound more like you're talking about carbueration except for the word "injector".

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thesmogman &raquo;</TD></TR><TR><TD CLASS="quote">Your close. When at idle with 18+inhg. the gas gets pulled from the injectors so lower pressure is needed when idling.

When off idle there is not as much vacuum pulling the gas through the injectors so the fuel pressure is increased. Not really increased but normal pressure.</TD></TR></TABLE>

yeah, you are close, except that makes no sense.. idle has nothing to do with it, its LOAD DEPENDANT. as load is increased vacuum decreases letting the diaphram in the fuel pressure regulator shut more increasing fuel pressure. the only time you have to worry about fuel being pushed/pulled into the combustion chamber is when you are boosted and the fuel pressure has to be high enough to overcome the boost.

OP: you can check the pressure with the line off or on, just make sure it matches the specs for whichever way you prefer to do it. i prefer with vacuum line on because if there is a problem with the FPR you will find out IMMEDIATELY. with the vacuum line off all you know is if its correct or not.

 

thanks everyone