Team Camaro Tech banner

6 psi fuel pressure with engine off???

8K views 27 replies 9 participants last post by  reelknots 
#1 ·
I noticed that there is 6 psi of fuel pressure to my Holley dp after the engine has been off for a few hours. Is this normal? I just changed from a fuel pump with a return line to the correct pump for my car. I didn't have this static pressure before...I guess because of the return line on the pump. My next move was to install an inline filter with the return line, the way it was originally equipped although I read that this was only on Q-Jets which mine was originally. Any comment or insight would be appreciated.
Thanks
Steve
 
#6 ·
I believe the guage is good. It read 0 this morning after sitting all night. Started it up, pressure was 8 to 9 then rose steadily up to 12 on fast idle. After the engine was off choke and idling at 800, the pressure came down to 9 to 10. I shut it off and the pressure stayed until I bled it. I ordered another new pump this time from a chevy dealer.
 
#8 ·
12 psi? Holy cow. Is this a mechanical pump and if so what's the gph rating? Usually anything over 110gph requires a regulator regardless of its rated pressure. My 110gph Summit (Holley) pump runs at 6psi and does not require a regulator.

They make several regulators for the 4150 an all of them have a max output of 9psi. A 4150 is supposed to have 5psi minimum and 7.5psi maximum. There is a specific one for the return line pumps.
http://www.holley.com/types/Fuel Pressure Regulators - Carbureted.asp
 
#10 ·
12 psi? Holy cow. Is this a mechanical pump and if so what's the gph rating? Usually anything over 110gph requires a regulator regardless of its rated pressure. My 110gph Summit (Holley) pump runs at 6psi and does not require a regulator.

They make several regulators for the 4150 an all of them have a max output of 9psi. A 4150 is supposed to have 5psi minimum and 7.5psi maximum. There is a specific one for the return line pumps.
http://www.holley.com/types/Fuel Pressure Regulators - Carbureted.asp
Yea, I seen the specs on the 4150 fuel pressure...that what is making me nervous. This is a brand new 4776-s 600 cfm and I don't want any problems with that. The fuel pump is the mechanical type from Auto Zone. It's rated at 7 to 9 psi....so what is happening when I se 12 psi!!! I ordered a AC 40726 pump from my Chevy dealer today. I hope this helps.

Thanks for the comments
Steve
 
#12 ·
Thanks, Steiner for your insight. This began when I noticed the pressure going to zero with my original mech fuel pump which had a return to the tank. When I pinched the return hose the pressure went up. Upon investigating on this site and the AIM, I found that my engine should have a two port pump (no return) and an inline filter with a return line. But this is only when the engine has a q-jet carb...since my car has a holley, I've tried to use the 302 as a model (small block with a holley). So I purchased an aftermarket replacement from AutoZone. This is the correct pump for a 350/300 h.p and a 302. So, either this pump is squirrelly and the new AC pump will be OK or I have some other problem.
If need be, I'm thinking of putting in the in-line filter with the return...but putting a regulator in the return line.
By the way, the instructions for the pump do not call for a regulator.

Thank you for your advice.
Steve
 
#13 ·
Ah, I see. All I can offer there is that those Holley's were 780cfm models and I have no idea what the pressure requirement was then but I'm with you on being nervous and would certainly try to keep it where Holley says it should be now.

I looked up that pump. If it's the $20 one, it's rated at 40gph which according to Holley's calculator is enough to feed close to 500hp at WOT.
 
#15 ·
Carter makes some nice musclecar pumps with the original look and style.

Here's the small block one. The gph rating is wrong...it's actually a 37gph I believe. Pressure is good though.

http://www.summitracing.com/parts/CRT-M6624/
 
#17 ·
Also keep in mind that fuel pressure gauges are notoriousely inaccurate. Particularly if they are fluid filled or inexpensive. Could be a bad gauge causing the 12 PSI reading.
 
#18 ·
If you purchased the fuel pressure gauge from autozone, I am 100% sure that the gauge is reading entirely wrong.
I have see their gauges (spectre brand) read over 9psi on stock fuel pump cars, the pressure also will make the needle bounce from 0- maxed out when the pump is pumping fuel.
 
#19 ·
I purchased the gauge from a local speed. It's a liquid filled Marshall gauge. I replaced the original gauge from Summitt because it bounced too much. I think the gauge is accurate since it read much lower on the second mech pump ( 0 - 1 psi ). I'm on my third pump now and waiting for my fourth to arrive!
 
#24 ·
I'm on my third pump now and waiting for my fourth to arrive!
The liklihood that you got one bad fuel pump is low. Three is impossible. I think there is something else going on that throwing money and fuels pumps at will not help.

I would think if there was a true 12psi while running it would push the fuel past the needle and seat and you would have extremely poor performance.

If the car is running fine then take the gauge off and don't worry about it. I raced mine for 10 years with no fuel pressure gauge. :D
 
#20 ·
Agreed. I got the Spectre dual-feed line from Autozone as a temporary/semi-permanent :))) fix because Classic Industries shipped me the wrong Holley dual-feed line and I got impatient and picked up the Spectre one from Autozone. It includes a little screw-in fuel gauge. Anyways, when running, the needle bounces around quite a bit, mostly between 4-7 PSI when idling.

It's been off for over 2 hours and I just went out and checked on it - it's still reading 6 PSI.

If it matters, I'm running a new (rebuilt?) Carter mechanical pump.
 
#22 ·
Agreed. I got the Spectre dual-feed line from Autozone as a temporary/semi-permanent :))) fix because Classic Industries shipped me the wrong Holley dual-feed line and I got impatient and picked up the Spectre one from Autozone. It includes a little screw-in fuel gauge. Anyways, when running, the needle bounces around quite a bit, mostly between 4-7 PSI when idling.

It's been off for over 2 hours and I just went out and checked on it - it's still reading 6 PSI.

If it matters, I'm running a new (rebuilt?) Carter mechanical pump.
LOL what else is new?
I bet if you tapped on the gauge the needle would fall back to 0 because it's just hanging in place.
 
#25 ·
The specs for the fuel pump he purchased state its running pressure is 7.5 to 9 psi which is too high for the carb (5-7.5 max) regardless of what the gauge says.
 
#26 ·
Just to clear up the number of pumps...I replaced the first pump because the pressure was close to zero. When the second pump went from 8 psi the first day to 1 to 2 after a few days...I replaced it but found out the first two were the wrong type anyway. They had a return line which is incorrect for a 69 350. So I went with the correct one from Auto Zone which is when the 12 psi started. I ordered one from my Chevy dealer which will arrive next week. So far I've spent $20 on the pump installed now and will pay $40 for the AC pump from chevy. So, I'll be out $20, which is OK if I correct this problem. If this doesn't work....I'm putting a regulator in the line.
Thanks for the comments
 
#28 ·
Just wanted to update you on recent developements. I put the new AC Delco pump on today...started the engine and....8.5 psi...Well at least it didn't climb to 12 when the engine warmed. I removed the guage and checked it against my vacuum/fuel pump guage and it was right on, so I went to my local speed shop and picked up a Holley regulator. I'm thinking this is going to be a pain trying to figure out where to put this thing. So I'm standing there and decided to start it up again...6.5 psi and holding steady!!! Shut it off....started it up...6.5 psi. So now I'm confused but happy I don't have to install this regulator. I can't explain what happened other than maybe this pump is a good one and somehow there was some vapor pressure in the line the first time...it's all good now but you can bet I'm going to keep a close eye on this pressure. Maybe now I can tune this carb like I was trying to do a couple weeks ago.

Thanks for the help
Steve
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top