Well not a vapor lock issue. Fuel pump?

B

BlackRat

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Mar 27, 2008
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Well I built a return line and it is returning fuel to the tank as it should. I know this because I did not have the hose clamp tight on the return tube at the top of the tank.

This time the front bowls went dry within the first 5 minutes of driving. Runs fine siting at an idle in the yard and the bowl does not run dry. I noticed that my fuel pressure guage is reading what would be less than 5psi and probably closer to 0!!!! My assumption is I am getting just enough fuel for idle but running is way to taxing. The guage is between the pump and the filter so I know that is not where the issue is. The fuel pump is a holley high volume about a year old. I am thinking that it is time to switch to an electric FP. Before I make this jump is there anything else that these symptoms point to???

Thanks
Wade
 
DeeVeeEight said:
Clogged fuel filter, bent/kinked fuel line, old degraded rubber fuel line (swells shut), clogged fuel line and lastly - a long shot - a non vented gas cap.
Click to expand...

Steel braided fuel line and I checked it all while running the return line. Fuel filter is also clean. The filter comes after the pressure guage so what ever is happening is occuring before the filter. I have a custom ground Isky cam on what I think is called a 9000 core???? Someone had suggested that I may have rounded the FP lobe out if it needed a bronze tip????
 
Return style pump? If not, you need a regulator or a pill...at least some kind of restriction to keep the float bowls filled, can't just plumb a return line off the carb.
 
Twin_Turbo said:
Return style pump? If not, you need a regulator or a pill...at least some kind of restriction to keep the float bowls filled, can't just plumb a return line off the carb.
Click to expand...

TT I took a barb fitting and JB welded the end shut. Then I drilled a 1\8" hole through the center of the JB weld. From an earlier post by Lars this was how I understood to build it. ?????
 
First thing first then, did you verify the pump is pumping at all? Can you snap a pic of how you plumbed it all? No fuel filter before the pump right?
 
Twin_Turbo said:
First thing first then, did you verify the pump is pumping at all? Can you snap a pic of how you plumbed it all? No fuel filter before the pump right?
Click to expand...

Unfortunately the battery is dead on the camera but it is pretty simple. However the return line was an attempt at solving the problem but it didn't.

On my 850 Demon I put a "T" fittingon the line where it goes to the back bowl. So coming from the pump I have braided lin going to an elbow with the FP guage to the fuel filter to a "T" with the middle port feeding the front bowl and the back port going to the 2nd "T" that feeds the rear bowl and the back port of that "T" having the barb fitting with the 1\8" orifice. I have a rubber line then running from the barb fitting all the way back to the tank and connected to the return port on top of the tank.

I know that the pump was pumping as I left the clamp at the return port on the tank loose. This caused a small fuel leak at the back. The car also ran at idle in the driveway for 10 minutes and made it on a 5 mile ride where it drained the fuel bowl when I got on it and I had to really back down for the supply to catch up.

The feed line from the tank is a one peice braided line all the way to the Holley mech pump.

I just don't know where this problem came from. I never had it till 2 weeks ago and that is what lead me to try the return.

:(
 
Could be gravity feeding enough for idle and low demand, still no proof the pump is actually pumping a significant amount of fuel. Could be anything from a leaking pump to a fuel pump lobe issue. There's no long bolt in the front motor mount hole, long enough for the pump pushrod to hang up on and not return to the cam base circle right (severely reducing pump stroke)?
 
The fuel is perking under point of max suck from the mechanical pump, that means the pump never gets a full mouthful to push up to the carb....

the line gets hot enough, demand great enough...

I remember fighting this in the past.....tossed the towel and stuck in a electric pump.....fixed it....

same diagnostic position you in right now.....bad mammories....

:suicide:
 
A couple of things:

1. I don't think I've ever recommended a 1/8" diameter fuel return oriface. I usually recommend a .060" diameter oriface in a non-regulated system using a mechanical pump. Anything larger than that can deplete a diaphragm type mechanical pump at WOT.

2. You can run well with fuel pressure at the carb inlet as low as 3 psi. Anything lower trhan 3 psi will cause fuel starvation.

3. Pull the tank pickup sock off - it is the usual point of restriction.

4. You can easily check to see if the cam pump lobe is rounded off by removing the fuel pump, disconnecting the ignition coil, and placing your finger on the pump pushrid while someone "bumps" the engine over with the starter. However, this seldom occurs due to the relatively low pressure of the pump on the cam lobe.

Lars
 
lars said:
1. I don't think I've ever recommended a 1/8" diameter fuel return oriface. I usually recommend a .060" diameter oriface in a non-regulated system using a mechanical pump. Anything larger than that can deplete a diaphragm type mechanical pump at WOT.
Click to expand...

I don't even remember what size I drilled but is was larger than .060" ... guess it's time to get some more JB weld and a smaller dirll bit...
 
Sorry Lars. I got the design from you but must have seen the 1\8" somewhere else.

Before I was running about 5-6 psi at idle. Now it is barely moving past 0 if at all so there is definately a restriction or failure somewhere. Is the pickup pretty easy to remove? If so that seems like the next thing I need to check before ultimately switching to an electic FP.

Thanks
Wade
 
Some time ago, I disassembled an old stock C3 fuel pump (destroying it in the process because I had to grind off the crimped metal at the diaphragm) to see how the return feature was implemented...

The return port was simply fed through an orifice of .058". Knowing the benefits of the return line, I added a return line to an old Edelbrock high volume fuel pump (originally 2-port) using this sized orifice and it works fine.

Cheers!
 
Well I pulled the pick up and it looks brand new. Sock was there and soft. No cracks or disentigration. The tank was new when I bought the car and it looks like the pickup was replaced as well. O ring was like new as well. I drained 5 gallons of Shell gas out of the tank before removing the pickup. When I disconnected the line it flowed strong with no restrictions.

So:
1. I have built a return line. Problem still exists.
2. Pulled the pickup and it looks like brand new.

Tonight I am going to blow the fuel line out with my air compressor. I think I am at the point where I need to just listen to mrvette and put an electric pump on this thing! I just wish I knew why this all of a sudden started to happen!!! This drives me nuts!!!

Lastly, Lars since we know the return line did not fix the issue is the 1\8" hole to big? I might as well reduce it now if so.

Thanks
Wade
 
BlackRat said:
Well I pulled the pick up and it looks brand new. Sock was there and soft. No cracks or disentigration. The tank was new when I bought the car and it looks like the pickup was replaced as well. O ring was like new as well. I drained 5 gallons of Shell gas out of the tank before removing the pickup. When I disconnected the line it flowed strong with no restrictions.

So:
1. I have built a return line. Problem still exists.
2. Pulled the pickup and it looks like brand new.

Tonight I am going to blow the fuel line out with my air compressor. I think I am at the point where I need to just listen to mrvette and put an electric pump on this thing! I just wish I knew why this all of a sudden started to happen!!! This drives me nuts!!!

Lastly, Lars since we know the return line did not fix the issue is the 18" hole to big? I might as well reduce it now if so.

Thanks
Wade
Click to expand...

Wade, be glad to tell you what happened to ME years ago, damned if I know, just know that electric pusher pump in the rear solved the problem forever....been my solution for cars for decades now, and of course with FI, it's a obvious....

:hunter:
 
Gene,

Where did you mount the pump? Any pic's? Also just to clarify you are using a Carter pump with no regulator and the mechanical FP was removed and blocked off correct?

Thanks
Wade
 
BlackRat said:
Gene,

Where did you mount the pump? Any pic's? Also just to clarify you are using a Carter pump with no regulator and the mechanical FP was removed and blocked off correct?

Thanks
Wade
Click to expand...

The problem was years ago on a 400-455 Pontiac, and so the fix was the Carter pump, I did it again to a Qjet car, years later, and the pump was too much so a regulator was put in, no more knocking the seat off the valve....

as I recall 4 psi kept it pretty happy....I know a AFB is fine with whatever the pressure was on the Carter pump....I dunno jack about Holley....

IMO, find a long wire and a friend's pump, coathanger that thing in there, cut/splice the fuel lines, jump the wires to the battery/starter and go for a ride.....pump in back near tank....
proves the point before you break your ass any damn more over this shit.....

GOD how familiar this all sounds....de ja vu all over again....:friends::stirpot:
 
I had a car come in that had similar symptons. Problem was in gas tank. An old cork gasket from the gas cap had broken into pieces and as the car ran would get suck up by the pickup tube and clog the sock. With the car running look in the gas tank for any obstruction or materials in the gas. DO NOT USE A MATCH OR LIGHTER to help you see better...
 
BlackRat said:
Well I built a return line and it is returning fuel to the tank as it should. I know this because I did not have the hose clamp tight on the return tube at the top of the tank.

This time the front bowls went dry within the first 5 minutes of driving. Runs fine siting at an idle in the yard and the bowl does not run dry. I noticed that my fuel pressure guage is reading what would be less than 5psi and probably closer to 0!!!! My assumption is I am getting just enough fuel for idle but running is way to taxing. The guage is between the pump and the filter so I know that is not where the issue is. The fuel pump is a holley high volume about a year old. I am thinking that it is time to switch to an electric FP. Before I make this jump is there anything else that these symptoms point to???

Thanks
Wade
Click to expand...

Buy a 1982 vette sending unit and mount a 1984 "g" code camaro/firebird low pressure pusher pump in the tank. Then use a 84 "g" code mechanical pump and you wont have a fuel problem again. GM did this on the 84-86 5.0 h.o f-bodies to cure vapor lock and it worked quite well, I had one and it never had issues. Maintained like 4-6 psi.
 
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