I just installed a brand spanking new Holley Black series fuel pump and 4-9 psi regulator also made by holley. Ive had the same setup previously, but the pump started leaking so I got a new pump under warrantee and got the regulator for the hell of it. Ordered a normal cast one and in the box was a nice new chrome one :cool: So i made out on that. But I seem to have a problem keeping the fuel pressure above 6 pounds. Especially if I drive a long ways, almost like vapor lock, but doesnt completely lock. If I drive for ~40mins to the track, the pressure will drop down to around 3 pounds. Also if I hit the throttle while watching the gauge, it drops down a 1/2 pound, but doesnt make sense to me since its an electric pump and should run a constant pressure.
I dont know whether it is because of the hot weather in addition to the non-coated headers, or if its something wrong with the pump or regulator setup. I have one side of regulator outlet with the gauge and fuel line to the carb, with the other going to the return line with a 3/8 NPT x 1/8 NPT reducer to keep the pressure up towards the carb, but have a 3/8 hose on that 1/8 NPT cause it was a stainless braided line I had laying around, but didnt think it was that cause it still should be hold the pressure back from the reducer?? correct?
anyone have any ideas why this is happening?? I need to get this fixed so I can spray already~! :jester :lol:


[Modified by 74VETTE, 11:28 PM 7/7/2002]

 

what im more or less asking is how can I get more than 6 psi at the carbs and saefty switch?
or is it safe to spray the nos if the fuel solenoid has around 10 psi since the supply is before the regulator, but the carb only has 4-5 psi since its after the regulator and im getting that 4-5psi reading on the gauge?
id rather figure a way to get the pressure up a bit though.
here is a bootleg schematic of my setup

thanks again
Chris

 

How close to a source of heat is your fuel pressure gauge, and is it liquid filled. If you have a liquid filled guage close to a source of heat, sometimes the gauge will not work correctly. On liquid filled gauges there is a small rubber plug on the side of it, when the gauge is hot and not showing proper pressure push on the side of the gauge a little to let a little air into it, the gauge should come up to proper pressure.

If this is your problem I had the same one. I could not figure out why the gauge would show proper pressure when I first started the car, then would go down when hot.

 

thanks 69 N.O.X. RATT, ill give that a try since mine is a liquid filled gauge and has that rubber plug. But im not too sure thats the problem....I rerouted my fuel lines over the blower duct for the heater and a/c and mounted the guage on the firewall. And, the FP safety switch is setting off a warning lightin the nitrous mastermind telling me the pressure is too low anyway, but its definitely worth a try....anyone else have any ideas.
here is how the lines are ran, notice the main inley goes into the bottom of the regulator, but before the regulator there is the "T" supply for the solenoid, and then an outlet going back to the tank and a supply to the carb with a gauge, the FP safety switch, and then the double pumper fuel line:

here is how they are routed over the ducts away from the heat.



[Modified by 74VETTE, 11:39 PM 7/8/2002]

 

I would also check voltage at pump when having pressure problems. Those holley regulators are known for pressure creep, they are not much just my 2 cents!!!

 

I'm looking at the pictures in the post, wish you guys would use smaller frames so I would not have to scroll. Anyway the type of regulator in the picture is a back pressure regulator and should not have a return to the tank unless it is very, very tiny. The back pressure regulator use the spring to open the valve, pressure in the outlet side of the regulator is applied to the diaphram and as the output pressure increases it will close off the valve. When pressure decreases it allows the valve to open and add more pressure. These type of regulators need no return line. The type of regulator found in most of your FI application works the oposite way. The spring holds the regulator closed, input pressure is applied to the diaphram when the input pressure is high enough to over come the spring it will open the valve and this excess pressure is relieved back to the tank, this one needs the return line. If you have the back pressure type, such as the one in the pictures, plug the return, you don't need it.

 

Excuse me, I looked at the picture again. That IS a back pressure regulator and it is hooked up wrong. The incomming pressure from the pump comes in the bottom, the regulated output pressure comes out of the two sides, BACK pressure regulator. Presently, what your gauge is seeing is the pressure that is returning to your tank. You can leave the gauge where it is, but you need to move the carb feed to the other side of the regulator and eliminate the return line. The output of this regulator is what is regulated, not the input.

 

thanks dry seals...
you seem pretty sure its a back pressure regulator, so im gonna presume that as well. it is a holley 12-501 to be specefic.
the gauge is actually on the same fittings that supply the carb....maybe you are seeing the line going to the fuel solenoid?
but anyway, like you said, I have a incoming fuel going into the bottom of the regulator, one side of the regulator going to the carb (and FP gauge in the NPT fittings) and the other returning to the tank (1/8 NPT).
the pump is a holley black pump rated @ 140 GPH (free flow) or 120 GPH at 9 PSI.
Do you think it would be safe to run this pump w/o a return line? If so, I could do away with the return line and put the supply to the fuel solenoid on the other side of the regulator and set it higher since it wouldnt have a return line. or would it be better to make a smaller return line somehow?
I really appreciate your help dryseals! its got me going in some direction now...let me know what ya think...
Chris

 

Took a trip to the Holley site, they show the pump and regulator in the setup as I described. My only concern is dead heading the pump. A return line is a good thing as it keeps the fuel circulating and cooler, but this realy requires a different type of regulator. Holley shows the pump being dead headed so it may well take the torture. I once had an MGB that had a pressure switch built into the fuel pump that would not allow the pump to pump past a fixed pressure, it would shut it self off and restart when the pressure droped off. Try re routing your lines without the return, bottom of regulator as feed from the pump, gauge and feed to the carb as one, plug the other side of the regulator. Turn on the pump but do not start the car, if the pump shuts down after a pressure builds, then they have the internal shut off. If it keeps spinning, it does not, but they may have a built in bypass to keep the pump from dead heading. I do not have a Holley pump or I could tell you for sure. The biggest problem with this type of regulator and a return line is there is no way to control the return volume. You could add a small valve on the return and restrict the flow but under high demands this return could hurt you. This is why the factory uses the other style.
Hope this helps.

 

Ok 74vette, here we go. If you are running stock fuel lines and your planning on spraying your ZZ4, forget it. If you are drawing fuel from the stock location, meaing the top of the fuel tank, there is a sock located in side the tank that will sometimes collapse, this causes the pump to be under load constantly and eventually will loose prime, especially in very hot weather. A simple solution is to install a Jegs or Summit sump in your tank that will allow the system to gravity feed itself. You can also weld a fiting in the bottom of your tank that works just as well. Then run 1/2 fuel line from the rear to front and get rid of those stock lines. Another tip, if you havent already done it, purchase a second nitros solenoid in order to prevent backfires. Trust me it helps..Good luck :cool:

 

dryseals, how do you think it would work out if I threw in a "T" right after the pump so it circles back to before the pump, so it doesnt just dead head the pump. Or what about "T"ing in a return before hte regulator and using the stock return line, but rather than going back into the tank, go back right before the pump like i said before?

tiresmokin75-427, on my '74 the main supply from the tank is on the bottom, the same spot as the fuel gauge sending unit. If I can maintain 6-7+ psi, do you think the fuel lines would still be suffucient for the nitrous? Also, why do you suggest buying a second nitrous solenoid?? Im still new to the nitrous picture, so why would it cause backfiring.
Thanks!

 

Hey 74vette, What ive seen happen is after you go through a few bottles of nos, the nitros solenoid can stick. It's scary because sometimes it will stick in the closed postition and you get fuel with no-nitros, and then all the sudden the solenoid releases and you get nitros at an improper mix with fuel causeing a backfire, which blows out the top of the carb. I called nos when this happened to me and they recomended at kit that they sell which includes a purge valve and a second nitros solenoid. Since installing it, I haven't had any problems with my big-shot. I don't have a scientifac reason why the larger line works. All I can is my friends at the local speed shop recomended 1/2 line when running nos with only one fuel pump. Most of my friends use nos and they say that the best way to run nos is to use two electric pumps, obviously one completely dedicated to the nos. This is the way Im going with my current project. I also use the same holley regulator you have and sometimes they do act a little strange with pressure readings, but so far I have had no major problems. Back to that fuel line, we used a 12,000 psi air brake line, with Aero-Quip reusable hydraulic fittings to plum the chassis.
It sounds cheap but it more than meets NHRA requirements and its 1/2 the cost of braided steel. Aluminumn is nice but I wanted a flexable safe fuel line Under the hood I have all Russell anodized fittings and braided steel, but since you can't see the fuel line under your car, well let's just say I needed the money saved to buy other parts. take it easy, Joe

 

wow...sounds like the engine compartment would look very cool with the anodized fittings!! I actually have a purge kit right now so I might be set so far....im gonna stick with my fuel lines right now, but im going to be checking the plugs after each run for the first few times to make sure all is ok.
good luck with your project!