During the 80's GM fuel systems used in tank electric fuel pumps and in line fuel pressure regulators. The pressure regulators are usually mounted on the rear frame rail ahead of the gas tank.

They are supposed to be adjustable and are mounted so the the adjustment can be done through a hole in the frame.

After I removed my engine fuel pump, the fuel pressure was about 9 psi. The Quadrajet carb likes about 4-5 psi. Unfortunately, the adjustment on my regulator was corroded and seized. I replaced it.

The regulator is identical to the current Holley #12-803.



It is located on the passenger side behind the rear spring mount:



Closer: (notice the adjustment screw and jam nut)



Here is the inside frame shot:



The regulator is made for 4.5 to 9 psi. It came about set about 6, I set it for 5 psi.

It was easy to change (changed a few fuel hoses while there) and costs about $25.

Upon returning from our first outing (2 days after purchace) I found fuel dripping from rear of coach. Result of cracked diaphram in regulator. My replacement was more work than your's as they had run the hydrolic lines for the jacks thru that access hole in frame. I had to drop fuel tank to replace. Mine is set at 4lb, I still have engine driven pump. From what I can tell they started using this setup mid 85's up. My 86 Chevy truck manual doesn't show the in tank pump or reg. Took a guess on PSI. Your pdf on vapor lock was the best info I have seen on this system.

Doorman

I had forgotten how much easier it is to work under my coach. Because of the tag axle, the coach is 8 inches higher off the frame, lots more room to work around the frame and tanks. I'm glad of that every time I go "down under!"

Nice writeup Steve!

Steve,
My concern is that the hose to the input of the regulator is held in place with a single rusty hose clamp, and that is a pressurized line.

Great info on the regulator. On mine, the regulator is the only part of the fuel system, other than the tank, that I have not yet replaced.
thanks!
Matt