I bought what is supposed to be and AFPR from a guy. What I got is an aluminum cover with the bolt holes all around the bottom flange, an inlet for fuel line, with an adjustable screw on the top, and a little round metal plate about the size or a quarter. Is that it? I assumed I would get a complete assembly with a bottom and something inside. I admit I have never messed with the fuel pressure regulator before.

So, is that what you get when you order a AFPR from Jegs for example? How the heck do you install it? Take of the rubber pieces on there now and bolt this on over whatever is in there? or what. Also, where do you put the pressure gauge if I get one later?
thanks

 

A fuel pressure regulator is simpy a valve that regulates fuel flow. It's mechanism for doing that is a vacuum diaphragm that works against a spring.

The spring pressure is what governs your fuel pressure/flow at any condition (pressure and flow are inversely related). Engine vacuum acts on the diaphragm which compresses or relaxes the spring, thereby opening or closing the valve. Under high engine loads (low vacuum) the spring overcomes the vacuum diaphragm, opens the valve and more fuel flows. Under low engine loads (high vacuum) the vacuum overcomes the spring and the valve closes (not all the way, obviously) and fuel flow is reduced.

That cap you receieved with the screw sticking out is what allows you to adjust the preload on the spring such that it takes more or less engine vacuum to overcome it. What you have to do is unbolt the black FPR cover from the TPI fuel rail and bolt this one on in it's place. Make sure that the little disc inside the cap centers up on the spring in the regulator. Once fastened, connect a fuel pressure gauge to your Shrader valve on the left rail and start adjusting your pressure.



BTW, that little nipple on the regulator is not for fuel. It's for an engine vacuum line. However, make sure it is not a timed vacuum port. It must be a constant source of vacuum- even at idle speeds.

 

Thanks for that info, it clear up a lot. ONe thing, where does the vacuum line come from? Is there not one on there now and I just disconnect it and connect to the new top piece? If I need to tee a vac line from somewhere, where it it usually done? thanks again

 

Whatever vacuum line came off the OEM piece, simply plug it back onto this one. It should come from the rear, passenger side of the plenum.

However, if you require a different source, simply find a line that has vacuum at all engine speeds and tee into it. Manifold vacuum is manifold vacuum- it doesn't really matter where it is sourced from

 

sounds too easy, haha. Hopefully there is a vacuum hose already on there and I can just switch it over. I don't remember, but it the stock FPR works the same as you describe, it must have one. I just adapted an LT1 throttel body to my TPI L98 and had to find another vacuum source for the EGR solenoid (as the LT1 throttel body doesnt have a fitting). Im still confused about what it ported vacuum and what is manifold vacuum. I mean Iunderstand the concept, manifold is constant which is what I need for the AFPR, and ported varies with TB position or engine speed, right? Im just not sure which is physically which on the motor.

 

Our AFPR provide a restriction on the return line, more restriction and you get more fuel pressure.

 

The stock FPR has the vacuum connection on it, so you don't have to search for it. Comes right off the plenum above it.

Since noone else mentioned it, the stock FPR is held on by tamper proof torx bits. Just like torx, except a little tit in the middle of the star so a regular torx bit won't fit in.

 

Well crap, does that mean Ive got to buy another tool or something. How do I get the sucker off then?

 

I just put the torx bit in the hole and hammered the "saftey button down"!

 

They make anti-tamper torque bits, just get an el cheapo set at Autozone or wherever. Mine have come in really handy for a lot of things. BTW, you can easily make your stock FPR adjustable simply by drilling a hole, tapping it, using an appropriate sized bolt w/a jam nut at the bottom, then drop a quarter in the other side.

 

It is called a security torx bit. Those bolts for your press. regulator are hard to find too. I wouldnt go hammering on them. For the record you cannot use a quarter under your FPR cover either, it is way too thick. Your fuel pressure will jump to over 50 psi! May make you way slower. The best and easiest AFPR i have seen is the Holley dial. Just turn it by hand, It is very hard to use the regulators that have the screw on top,as they hit the bottom of your plenum.

 

I dunno, mine reads 43 psi at idle, isn't that close to factory spec?

 

As far as i know 43.5 should be stock.

 

Tested my 92 LB9 recently, 35 psi . . WTF?

 

From what I understand it should be around 43 psi with the vacuum disconnected and plugged. When you plug in the vacuum it will drop like 8-10 psi. So if you checked your fuel pressure while the vacuum was still plugged in 35 psi sounds normal.