6 psi fuel pressure with engine off??? - Team Camaro Tech
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post #1 of 28 (permalink) Old Oct 14th, 09, 07:39 PM Thread Starter
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6 psi fuel pressure with engine off???

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.
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post #2 of 28 (permalink) Old Oct 15th, 09, 04:28 PM Thread Starter
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Re: 6 psi fuel pressure with engine off???

34 looks and no comments?? Somebody must have a fuel pressure gauge in line with a Holley 4150.

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post #3 of 28 (permalink) Old Oct 15th, 09, 04:35 PM
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Re: 6 psi fuel pressure with engine off???

I can't say if it's normal or not but will say that mine does the same thing and has for years. Even after a few days they'll still be a few lbs.psi on my gauge. I do not have a return line on my car. So based on my experience would have to say it's normal.
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post #4 of 28 (permalink) Old Oct 15th, 09, 04:52 PM Thread Starter
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Re: 6 psi fuel pressure with engine off???

Thanks, Bill. I'm also a little worried about the 12 psi while running. I've ordered a GM pump to try out. I currently have the replacement from Auto Zone.

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post #5 of 28 (permalink) Old Oct 15th, 09, 06:10 PM
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Re: 6 psi fuel pressure with engine off???

Are you sure the gauge is good 12 psi seems to high for me.6 to 7 psi is what I run on my 850 Holly.My gauge stayed on 6 psi for a while but now returns to zero I guess this was for about the first 500 miles.

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post #6 of 28 (permalink) Old Oct 15th, 09, 06:30 PM Thread Starter
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Re: 6 psi fuel pressure with engine off???

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.

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post #7 of 28 (permalink) Old Oct 15th, 09, 06:36 PM
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Re: 6 psi fuel pressure with engine off???

I wouldn't worry about the static pressure, but is the fuel emptying into the carb bowl and over flowing into the intake?

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post #8 of 28 (permalink) Old Oct 15th, 09, 07:14 PM
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Re: 6 psi fuel pressure with engine off???

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%20P...Carbureted.asp

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post #9 of 28 (permalink) Old Oct 15th, 09, 07:38 PM Thread Starter
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Re: 6 psi fuel pressure with engine off???

Quote:
Originally Posted by Everett#2390 View Post
I wouldn't worry about the static pressure, but is the fuel emptying into the carb bowl and over flowing into the intake?
I don't see any evidence of fuel spilling over into the intake. Wouldn't the pressure bleed down if that were happening?

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post #10 of 28 (permalink) Old Oct 15th, 09, 07:42 PM Thread Starter
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Re: 6 psi fuel pressure with engine off???

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Originally Posted by Steiner View Post
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%20P...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

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post #11 of 28 (permalink) Old Oct 15th, 09, 07:56 PM
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Re: 6 psi fuel pressure with engine off???

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Originally Posted by reelknots View Post
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
If it's a 7-9 psi pump, it's already too much pump. I would assume that it is a pump designed to be run with a regulator and would be surprised if the paperwork that came with it didn't say anything to that effect. Even Dominator carbs are rated for a max pressure of 7.5psi. Running it on a 600 carb with stock smallish jets the pressure is going to be high at idle as there is no load and very little fuel required. Running at a fast idle still doesn't require much fuel but you're running the pump faster and there's nowhere for the extra flow to go. Your floats should be shutting down the bowls so there's just nowhere for that fuel to come in and the pump is pumping against the closed inlet valve. I wouldn't be surprised if running at that high of a pressure for too long wound up messing up an inlet valve so it won't seat properly so getting the pressure down would be a good thing.

You will probably be good with the AC pump. The Summit 110gph small block pump runs at the perfect pressure of 6psi for my carb (I have a 4150-based 670 Street Avenger). It's only around $55 I think. You probably only need the 80gph model with a 600 though if you're not running more than 400hp or so as it would be plenty.

A regulator is a little less than another pump though.

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Last edited by Steiner; Oct 15th, 09 at 08:08 PM.
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post #12 of 28 (permalink) Old Oct 15th, 09, 08:24 PM Thread Starter
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Re: 6 psi fuel pressure with engine off???

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

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post #13 of 28 (permalink) Old Oct 15th, 09, 09:01 PM
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Re: 6 psi fuel pressure with engine off???

Quote:
Originally Posted by reelknots View Post
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

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.

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post #14 of 28 (permalink) Old Oct 15th, 09, 09:21 PM Thread Starter
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Re: 6 psi fuel pressure with engine off???

Quote:
Originally Posted by Steiner View Post
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.
That's the one, and my 350 is supposed to be 300h.p. but I'm looking for a nice Sunday cruise vehicle that looks original and not anticipating doing the quarter unless I put it in my bucket list!! I'm hoping the AC pump I ordered will put this issue to bed. I appreciate your comments that re-inforce my thoughts or provoke more.

Regards
Steve

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post #15 of 28 (permalink) Old Oct 15th, 09, 09:27 PM
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Re: 6 psi fuel pressure with engine off???

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/

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TKO 600-Moser 3.42-Detroit Truetrac
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