>>> holley bypass regulator 12-803bp ???
 

Has anyone had experience using a Holley 12-803BP bypass fuel-pressure regulator to stem the pressure of a high-pressure piston lift-pump ??

Some years ago, I bought several new-in-box genuine Carter Made-in-USA piston lift-pumps with an un-familiar part-number and no idea of pressure output; of course, I bought these accordingly --- as in cheap.

Until today, these pumps have sat high on a shelf awaiting some time of need.

I plumbed in the 14x1.5 X 06JIC Metric adapters, replaced the bolts with McMaster-CARR studs, slathered Form-a-Gasket #2 on all sides of both gaskets, sandwiched in the 3/16" spacer, and mounted one of these bargains of un-known credentials onto an engine.

While I watched under the hood for any drips or floods of fuel, the wife pressed the starter-button, the 6BT jumped to life, and I watched the 16-PSI gauge immediately climb past 16 ---- shut-'er-off

From the moment I placed the final bid on E-Bay, until the moment I watched the gauge max-out, I had held to a hope that these mysterious piston lift-pumps would fall in the 5- to 15-PSI range ---- alas.......... :(


That leaves me with a second question:

Considering this is a daily-driven all-purpose work truck that is driven with some sense, once I get a proper bypass regulator installed, will it suffice to TEE the bypass into the O.E.M. return line ??



OR, should I utilize the O.E.M. DRAW line as the bypass return and install a new 3/8 DRAW line all the way to the tank ??


Your educated wisdom please.

Thanks for reading.

I just got a low pressure spring from the hungry diesel.com he has 3 different pressure springs. they are spendy, but you end up with a much simpler system. and a high volume pump to boot.

Thanks for making me aware of The Hungry Diesel; I did not know they existed.

Which PSI spring did you get ??

If I decide to go that route, I am leaning toward the 12-PSI spring.

Fifty-bucks for a spring sort of makes me flinch; but it is cheaper than a $70 regulator, 12- to 15-feet of hose, a bulk-head fitting for the tank, fittings for the regulator, Teflon tape, and a handful of 99-cent clamps, plus various accoutrements that I haven't yet thought of.

But then, nobody will ever see that spring; whereas, they could stare in awe and amazement at all that extra plumbing and shiny new regulator.


Thanks for the info.

OKAY, I went deeper and dis-assembled two of these E-Bay pumps; here is what I found:

The internals appear to be identical to the 3936320/4944714 low-pressure pump that we are already familiar with; however, these are definitely high-pressure pumps; maybe they are high-pressure/low-volume pumps for a 4BT application or somesuch.

The piston-bore has a brass sleeve.
Piston O.D.= 1.019

The spring is shiny --- not black --- and is tapered --- not straight.

These springs are "chrome-colored" ; whereas, the tapered spring pictured in BC's article (see below) appears to be "gold-plated" , possibly denoting it to be low-pressure.

https://www.dieseltruckresource.com/...d.php?t=176472


Are the HungryDiesel low-pressure springs STRAIGHT or TAPERED ?

Thanks.

If I were in yer shoes.......
I would document the dimensions, and the rate of the spring you have in your hand. Then I would hike over to a hardware store or auto supply that has a decent supply of springs, and buy one with the same dimensions and half the rate. Probably a few bucks.

That thought has been lurking amongst the many others floating around in my skull.

It would be a simpler matter were the spring straight instead of tapered.

Thanks.

I e-mailed the particulars to the hungry diesel guy and his reply was that the springs he had would not work in the smaller piston that requires the tapered spring.

I finally found the Cummins number for the pumps I have:

3936323

From all my research, I believe the only difference between this pump and the low-pressure 3936320 is the color/stiffness of the spring.
The 3936323 spring is silver with wire diameter of 0.122; the 3936320 spring is gold and I do not yet know it's wire diameter.

It appears all avenues of relief have ended in blind canyons, so unless I find a better solution, I will be learning first-hand about the Holley by-pass regulator.

Although it is more plumbing under the hood and a third fuel-line under the truck, a big advantage of the regulator is that, in the unlikely event the pump ever fails far from home, it can be replaced with whatever Carter piston-pump I can lay hands on with no concern as to out-put pressure.

Now, I just gotta dig up enough money to get it on the way.

BK, when I installed a Walbro GS392 with a Holley 4307M regulator on an old truck, I did TEE into the stock return line. I cut below, tank side, of the quick connect fitting, put a couple rubber hoses on to each end, a brass T in the center, and clamped them. Ran 10k miles and the sold the truck. No problems. I could here the return in the tank IF I was low on fuel.

Just a thought. You might try cutting a little off the bottom of the spring and test it. A lot of trouble but in a vice it should be doable. I have don that on a pressure switch. Mike

Thanks for the idea; alas, were it a straight spring I would have already tried that; however, it is a tapered spring and the ends must remain the same diameter.

The little end fits into the hollow piston and the big end fits the un-sleeved portion of the cylinder.

Also, the way these pumps operate, the spring cannot be any shorter than it is; the spring keeps the piston in contact with the operating plunger.