Build your own adjustable fuel pressure regulator ;)

[oldeskewltoy]

I decided to make a guide as to how to build your own adjustable fuel pressure regulator. The TOM'S unit is over $300 on ebaY, and most of the other types require moving the regulator mount off the fuel rail and onto the firewall. B&M has been selling a kit for over 10 years that, although specified for use on Hondas, works perfectly well on our FPR too.

Here is the product: B&M 46058 is the part number. The cost is between $35 and $55... (far cry from $300 )



Because it is being used on a Toyota, there is a need to make one of 2 modifications. 1) add a 2mm thick rubber seal shaped to the same size as the original seal (shown below) OR have the upper housing machined down 1.5-2.0mm (actually machined "up" in this case)

You begin with any of the 4AGE FPRs, this will work on a 20V FPR as easy as it does on the 16V.



Here is a 16V fpr, mounted on a rail. First you remove the 2 bolts, and gently twist the fpr to ease removal. Remove the fpr, put the rail aside.


Using a Dremel, or other cutter, cut all the way around the edge of the FRP. Not too deep, about .5mm-1mm depth is deep enough.


Once you have cut 3/4 of the way around, the spring inside will be "pushing" on the lid of the FPR.

Note the thin gasket inside I referenced above.

The key dimension is the overall diameter of the fpr, and the machined inner diameter of the B&M fuel pressure modifier. These are PERFECT.

The only problem is as suggected above, the base of the Toyota FPR is not thick enough to be tightened in place with just the flange that is part of the assembly. You can kind of see the assembly disappear inside the B&M housing. As I alluded too @ the beginning, you can have the bell part machined down about 1.5mm, or you can replace the wafer thing gasket with a much thicker one. In either case the cost to do the mod is at maximum $20(to pay someone to machine the housing)

The Toyota spring is longer than the one in the kit, I retained its use for now, *IF* I find the original spring is too tight, I'll disassemble the unit and install the spring that came with the kit. The reason I retained the original spring is the height inside the red chamber is actually taller, and the smaller spring applied nearly no pressure when I first installed it. As I alluded too, I'll hold on to it for now and if the std spring is too tight without adjustment, I'll move to the spring that came with the kit.


Well, here is the unit assembled, and remounted on the fuel rail.


the vacuum connection is at the top of the adjuster

[oldeskewltoy]

from another forum Wrote:Nice write up, but that looks like ass (no offense). Have you pressure tested it? What's the pressure threshold before it starts to leak?

maybe this photo better shows...


It NEVER leaks**... the small rubber seal is not the diaphram to seal out fuel, but to make a vacuum seal. The diaphram is still intact, and it is part of the reason to not cut too deeply. All you are doing by removing the top is removing the set height for the spring pressure. The spring rests on a steel cup attached to the diaphram.


** obviously if you have a leaking FPR before, it will still leak after.

[Bean]

very nice write up Dan

after a quick search I found this how-to and wondered if one would cut the 4A-GE regulator just flush between the flatish surface and vacuum nipple (without cutting too deep to not harm the spring), if this would make the need for the modification redundant - not sure if there is a 1.5-2mm gain to be had from that but maybe worth a shot. Only concern I'd have that way is if the top surface where the B&M is resting on collapses/folds...

on another note have you made any measurements (bolt spacing, diameter and depth of the piece that goes into the rail)?

if I remember correctly bolt spacing is 39mm and the protrusion is 10mm deep on a 11m diameter - I'm not sure on these figures at all though.

reason I ask if I'm not completely mistaken the Impreza WRX (GDB; 2010-) uses the above dimensions. Most Nissan, Mazda and other Subaru have the same dimensions for the protrusion but the bolt spacing is only ~32mm. Last but not least Hondas have the same bolt spacing (some are offset!) but no protrusion at all but seal with an O-ring.

PS: stock pressure at idle on the 16V (I assume 20V too) is 38-44psi (2.6-3bar) with vacuum signal disconnected and 30-33psi (2-2.3bar) with vacuum signal.

[oldeskewltoy]

Bean Bandit Wrote:very nice write up Dan

after a quick search I found this how-to and wondered if one would cut the 4A-GE regulator just flush between the flatish surface and vacuum nipple (without cutting too deep to not harm the spring), if this would make the need for the modification redundant - not sure if there is a 1.5-2mm gain to be had from that but maybe worth a shot. Only concern I'd have that way is if the top surface where the B&M is resting on collapses/folds...

The problem is the FPR would be too wide @ the seam. I cut through the edge of the top, and remove it. It is only after the top is removed that its outer diameter matches the inner diameter of the B&M case

[oldeskewltoy]

Bean Bandit Wrote:on another note have you made any measurements (bolt spacing, diameter and depth of the piece that goes into the rail)?

if I remember correctly bolt spacing is 39mm and the protrusion is 10mm deep on a 11m diameter - I'm not sure on these figures at all though.

reason I ask if I'm not completely mistaken the Impreza WRX (GDB; 2010-) uses the above dimensions. Most Nissan, Mazda and other Subaru have the same dimensions for the protrusion but the bolt spacing is only ~32mm. Last but not least Hondas have the same bolt spacing (some are offset!) but no protrusion at all but seal with an O-ring.

20V also has offset spacing. I used a 20V TOM'S on my 16V (paid $50 for it on YJ) I have the fuel return running between the manifold runners 3 and 4

[Bean]

did some more googling and apparently there is also another version of the B&M for the Mitsubishi Eclipse, the vacuum take-off is on the side but I haven't found any other info regarding size etc...

I found one comment though that mentioned the B&M regulators being rising rate so not 1:1 - mind you this is of the net and could be wrong or right...

[BOOMEX]

It's exactly the kit i want to use when i'll put my MS.

Nice write up

[oldeskewltoy]

Bean Bandit Wrote:I found one comment though that mentioned the B&M regulators being rising rate so not 1:1 - mind you this is of the net and could be wrong or right...

the only change that this unit has that the original doesn't..... you can adjust spring tension... everything else operates as it does with the stock unit

BOOMEX Wrote:Nice write up

thank you

[AlexKTM]

very nice work, thanks for taking the time! it will surely come handy