Vac. / FP - something seems screwy

[Paul Clark]

At the hose going to the FP regulator my car has 17+ vac..
That's a good thing, yes?
FP hose off is 43.
FP hose on is almost 40 (39+).
That isn't right, is it?
Shouldn't there be a bigger variance?
(Accufab)
Is something plugged up somewhere, or do I get to order more new parts?
Thanks

 

[Ormand]

The 17+ you are reading is inches of Hg. That translates to about 7 or 8 psi. So the fuel pressure should go down that much, at idle, to something like 35 or 36. If you only get 40, that's not good. There may be a restriction the return line, that limits the fuel flow back to the tank.

 

[Back_in_Black]

My Vac at idle is about 16, I have the accufab regulartor. My fp is set to 43 line off, when I put the line on mine goes to 39 as well.

 

[Paul Clark]

I've never messed with the return line before.
How can I check it - and/or the regulator?
Thanks

 

[Paul Clark]

Another question.
The FP regulator itself limits the fuel flow back to the tank, correct?

 

[pacecarta]

i had same issue , i found if i backed the regulator screw off i couldnt get any lower than 39 , after going over the fp regulator lines and verifying vac and pulling the fp reg apart , and checking return for kinks restrictions , even blew shop through the return line i didnt have the answer

then i tried bypassing the hotwire and going to the original pump feed and low and behold the pressure could now be backed way down and my drop line off vs on was what it should be at ,7-8psi lower than the base setting of 43 , plug in hotwire and it was back at 39 line on , obviously the extra voltage ( 3v over stock harness) had an affect on pump volume and with hotwire340 the return line cant flow enough to have FP lower than 39psi

so yes fp regulator limits pressure by bleeding off excess pressure , only fix i can see is if running the hotwire 340 is to increase the return line size or
i thought about drilling the return orifice size slightly larger in the base of FP regulator

 

[Brian Harper]

i had same issue , i found if i backed the regulator screw off i couldnt get any lower than 39 , after going over the fp regulator lines and verifying vac and pulling the fp reg apart , and checking return for kinks restrictions , even blew shop through the return line i didnt have the answer

then i tried bypassing the hotwire and going to the original pump feed and low and behold the pressure could now be backed way down and my drop line off vs on was what it should be at ,7-8psi lower than the base setting of 43 , plug in hotwire and it was back at 39 line on , obviously the extra voltage ( 3v over stock harness) had an affect on pump volume and with hotwire340 the return line cant flow enough to have FP lower than 39psi

so yes fp regulator limits pressure by bleeding off excess pressure , only fix i can see is if running the hotwire 340 is to increase the return line size or
i thought about drilling the return orifice size slightly larger in the base of FP regulator

I had exactly the same problem. With the stock regulator on the car, adding a hotwire kit and putting in the Wlabro 340 raised my vacuum-line-off fuel pressure to 43 psi. Even with a new adjustable FPR I had to back it way off to get the pressure down to about 38 psi. BLM's at idle went from 130 to 110 with the new pump / hotwire kit so its definitely trying to push more fuel in there.

 

[Ormand]

There are a couple of fittings in the return line that are restrictive on some cars. I have read of people using a drill to open up those fittings, but I don't remember the specifics. Easy way to check is to take the line loose at the bottom of the regulator. Run a hose from there to a five gallon can, then check to see if the pressure drops down. If it does, then the return line is the restriction.

 

[TurboDave]

i had same issue , i found if i backed the regulator screw off i couldnt get any lower than 39 , after going over the fp regulator lines and verifying vac and pulling the fp reg apart , and checking return for kinks restrictions , even blew shop through the return line i didnt have the answer

then i tried bypassing the hotwire and going to the original pump feed and low and behold the pressure could now be backed way down and my drop line off vs on was what it should be at ,7-8psi lower than the base setting of 43 , plug in hotwire and it was back at 39 line on , obviously the extra voltage ( 3v over stock harness) had an affect on pump volume and with hotwire340 the return line cant flow enough to have FP lower than 39psi

so yes fp regulator limits pressure by bleeding off excess pressure , only fix i can see is if running the hotwire 340 is to increase the return line size or
i thought about drilling the return orifice size slightly larger in the base of FP regulator

Hot wired 340's can many times overwhelm the system, as some of you are discovering.

 

[Paul Clark]

So, is this a bad thing?
Should I go back to the stock wiring?
Problem is, I've had that pump in there for quite awhile and I don't remember the pressure variance being so slight until recently.
Thanks

 

[Ormand]

No, do NOT go back to the stock wiring. If the regulator won't control the pressure from a Walbro340, with good wiring, that's a problem in the regulator, or the return line, it is NOT an indication that you need to risk the motor by going to less pump volume.