FP Regulator bad?


I adjusted my Accfab FP regulator down (because of low BLMs) to 43 psi with the vacuum line off (engine hot by the way). When I reconnected the vacuum line, I noticed the fuel pressure only dropped 2 psi (to 41 psi). Shouldn't the pressure be 37 with the line on?

If so, is my problem a bad FP regulator or is the amount of vacuum at idle insufficient to properly change the fuel pressure? I didn't have a vacuum gauge connected during the FP check but I can hook one up if need be.

I'm thinking its a bad regulator and if so, what do you recommend for a replacement?

Thanks in advance for your help.
check the vac source for leaks , fuel pressure should drop 1psi for 1 psi vac when line connected which if looking at a vac gauge that reads in/hg it should drop pressure half of the vac reading . typical vac at idle sould be around 18 in/hg so drop should be around 9psi
also the regulator can only go down as far as the return line will allow , if you have a high flow pump and a hotwire you may not be able to get it lower without improving the return line flow
Thanks Doc. I just came in from measuring the vacuum and its 18 - 19 inches. I looked at my f/p gauge and it showed 41 psi, then I pulled the vacuum line to measure it, looked back at the gauge and it still showed 41. No drop at all!

I do have a high flow pump and hot wire to it. Are you suggesting I need a larger return line? The fuel feed and return lines are the originals from 87.
you measured 18 at the line going to regulator,
try running pump with the hotwire disconnected by rear bumper and running on oe wiring and see if pressure will go lower
Apparently when I ran the hot wire I cut the oe 12V wire where it goes into the tank and connected the hot wire instead. Car won't start without hot wire. To use the oe wiring only, I'll have to rig up a jumper from the oe connector to the hot wire at the tank. I can try this tomorrow.

What's your thinking for this test? I wouldn't think the voltage drop difference would be that different at idle. Don't know.
just seeing if press would go lower indicating too much supply for your return line
could be a restriction , a kinked line, filter bocking return in the tank , bad rubber hose over axle or on tank .. or it could be regulator

if you disconnect return line at frame and run it into a fuel tank (or through a hose back to the tank neck) and your pressure can be adjusted down your return line is restricted or pump is too big

if you have the stock regulator you could try that to see if it is the accufab
Dang, pacecarta.

Thanks for being here and answering the tech and or general questions of the "unwashed masses, :)" without fail. Always good, solid, grounded in the past/recent history tech answers.

I, for one, appreciate your willingness to do so.

Too many folks here have become discouraged and no longer proffer their deep, deep experience and knowledge because wisenheimers that don't want to hear they may have made a mistake and challenge these incredibly smart and experienced bunch with angry vitriol for merely giving concrete advice, it's so sad. Sorry for the run on sentence.

Dilly, Dilly!!!!!
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^^^^^^ The above comment has nothing to do with, nor was it directed at, the OP and/or his attempt to fix his problem, I sincerely hope you get it resolved.
I used a handheld vacuum pump to test the FPR and at 18 in/hg there is a slow leak. I was hoping it wouldn't hold at all but no such luck. By the way, the pump is a Walbro GSS340M (255L/hr - high pressure) installed in 2010 with new filters. The feed and return lines are original from factory. I'll do the return hose to gas can test next but shouldn't this pump be ok for my car?
it shouldnt leak at all ,
if you applied 18 vac to top of gate fp should have dropped if not either the regulator is the restriction or the lines have a restriction
do you have a stock regulator to try
I found an old Bosch 237 FPR that was crushed to make 50 psi (line off). I installed it with my hand pump connected to the vacuum port. Interesting results:
0 vac = 50 psi
10 in = 46 psi
18 in = 43 psi
20 in = 41 psi
24 in = 41 psi
26 in = 41 psi

So apparently my return line is 'stuck' at 41 psi, which matches my lowest number with the Accufab.
Doc, what would you do 1st if this was your car?
find the restriction

you can start with the line above axle , run a hose to a jug or run into the filler neck and see if pressure drops .if it does the restriction it\s between there and the regulator , could be a kinked steel line ..you need to find the restriction or replace the line
if presure is good with over axle line routed to a jug then restriction is in the hanger assembly in the tank , could be the fuel fitler is blocking the return tube that the pump hangs on
on the return line from regulator and at frame there are saginaw ends and you can significantly improve the flow of that line by wiggling an awl into the tip and widening that area a little bit where the oring hangs
I really appreciate your help, I'm getting a little frustrated here and your advice / knowledge is all that keeps me going. The thought of dropping the gas tank (again) is not very appealing.

I have to get some more fuel hose before I can do the first test. Any advice on where to get the hard line 0-rings? I need them at the fuel filter too. I'm assuming that the bottom of FPR and input to filter take the same size.
Dorman makes an assortment pack of Vinton o rings. They can be found at most crap auto part stores. Did you drop your gas tank previously? Just make sure that you know the smallest line to the tank is the return line. The other is the vapor return.

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