Engine sputter and no power over 5000 RPM

[Paul G]

I have a problem to figure out. 1973 440 727 auto, mild cam in rebuilt engine, Eddy intake Holley 750 carb, duals with H-pipe.  Going to full throttle from a 30 MPH roll the trans dropped down to first gear like it should. The engine revved to about 5200 RPM and then started to sputter and lose power. The trans shifted to second, RPM dropped and the engine took off again. I didnt let it rev over 5000 again.

How high should the engine normally rev before it loses power?

I have a Holley Red electric pump. The fuel line to the carb has a tap with a gauge on it. The gauge reads about 1 PSI at idle. They had ran this B.S. return line set up through the fuel filter. The fuel filter has a single inlet with dual outlets. The smaller outlet went to the return line.  I blocked off the return line and the fuel pressure went up to almost 3 psi at idle. When the engine is revved fuel pressure goes up to maybe 4 psi.

What kind of fuel pressure should I expect ?

[firefighter3931]

Paul, your fuel pressure is way too low. You should be seeing at least 6psi at all times, particularly at wide open throttle. Sounds like the engine is starving for fuel. If your float levels are set correctly, it's a fuel delivery issue.

Ron

[Paul G]

There is no regulator in the system. The sending unit and sock were replaced this winter. The hoses are new. Is there a way to measure the output from the pump? Other than that could the pump itself be going bad?

[firefighter3931]

There is no regulator in the system. The sending unit and sock were replaced this winter. The hoses are new. Is there a way to measure the output from the pump? Other than that could the pump itself be going bad?

It's possible that the pump could be going bad. There's a test you can do to determine how well the pump is working. It's called the 1 gallon test ; drop your fuel line into a 1 gallon container and turn the pump on. It should take less than 30 seconds to fill the container.

There could also be a low voltage issue at the pump....make sure it's getting sufficient power. Another issue could be fuel line diameter....too big of a line will drop pressure. The fuel filter could also be creating some restriction. just some things to look at.

Ron


Ps. I'm surprised that you're not using a regulator...most electric pumps require one to keep pressure in check. What type of fuel pressure guage are you using....is it liquid filled ? where's it mounted ?

[Paul G]

Ps. I'm surprised that you're not using a regulator...most electric pumps require one to keep pressure in check. What type of fuel pressure guage are you using....is it liquid filled ? where's it mounted ?

I was just on the Holley site and they say with a Red pump a regulator is not required. The gauge is a little chrome one that came with the chrome fuel inlet line for the carb. It is a Marshall gauge, not liquid filled. I will try doing the gallon test and see what happens.

[Paul G]

Did the gallon test. Are you sure it should fill the gallon container in 30 seconds? I got about a quart in 30 seconds. So I took a look at the fuel pump since Holley says it's adjustable. I found a screw in plug that has a spring behind it. I stretched out the spring a little and got it up to 6 psi varying to 8 psi. I did the gallon test again and still only got about a quart.

[firefighter3931]

Did the gallon test. Are you sure it should fill the gallon container in 30 seconds? I got about a quart in 30 seconds. So I took a look at the fuel pump since Holley says it's adjustable. I found a screw in plug that has a spring behind it. I stretched out the spring a little and got it up to 6 psi varying to 8 psi. I did the gallon test again and still only got about a quart.

The pressure sounds good with the adjustment....but you're still not getting enough volume. The 30 second gallon is correct for a fast street car (high 11's - low 12's) so if yours was slightly slower i'd say maybe a gallon in 35-40 seconds max.  Either the pump is on it's way out or there's a major restriction somewhere in the system. You're only at 25% of where you should be.....

Did you remove the fuel filter for this test ? If not...maybe run the test without the filter or return line to see what you've got. Also have a look at the voltage to the pump.....make sure you're getting enough juice to power it properly.


Ron

[Chryco Psycho]

make sure the timing is not overadvancing as well & do you have the cam specs ? fix the fuel problem first though & see if the problem persists , sounds like the fuel is the issue from what you have posted so far though, is there any restriction or older hose in the fuel sysytem ?

[Paul G]

I checked voltage at the pump. With the engine running battery voltage is about 13.5, at the pump I am only getting about 12 volts. I am going to wire in a fuel pump relay since it doesn't have one. I guess the best place to get power for the fuel pump relay is from the hot side of the start relay on the firewall. I will run a new 10 or 12 gauge wire all the way back to the pump.

make sure the timing is not overadvancing as well & do you have the cam specs ? fix the fuel problem first though & see if the problem persists , sounds like the fuel is the issue from what you have posted so far though, is there any restriction or older hose in the fuel system ?

All the fuel hoses are new. The steel fuel lines are original. All 3/8" lines. On the Holley web site they say to use two fuel filters in tandem between the electric fuel pump and the gas tank. My fuel filter is placed up by the carb. Holley wants the fuel pump mounted vertically and lower than the fuel tank. My fuel pump is mounted horizontally under the trunk floor above the leaf spring. There is no clearance to mount the pump vertically lower than the tank because of the leaf spring.  ?

Should I relocate the filter between the pump and tank, and use two filters? Is it that important? Where is a good (better) place to mount the pump?

[firefighter3931]

You might have to fabricate a bracket to mount the pump lower. I wouldn't worry too much about filters at this point because fuel delivery (volume) is a problem. You need to correct that first.

Ron

[Chryco Psycho]

I prefer to have the filter after the pump near the front , it takes far less restiction on the suction side to starve the pump /engine for fuel

[Paul G]

I installed a relay today. Used 12 gauge wire all the way to the pump. It brought the voltage up to right at 13 volts at the pump. Did the gallon test again. I am getting about a half gallon in 30 seconds now. I am surprised 1 volt could make that much difference. I removed the fuel filter and still got about half a gallon. Moved the filter before the pump like Holley suggests and still get half a gallon. That puts the pump at about 60 gallons per hour when it's rated at 71. It maintains 5 PSI now as well. I need to go do some full throttle runs now and see how it responds. I was looking around under there by the pump. I could make an angle bracket and mount the pump under the frame rail just between the spring and the exhaust pipe. It will be easily visible from behind. That might look kinda cool.

[firefighter3931]

Hey Paul, that sounds like a step in the right direction.  Low voltage will certainly affect output, i've seen it happen before and that's why i suggested you check it.

Hopefully the relay and heavy wire does the trick. 


Ron

[Rolling_Thunder]

does ur car have a 3/8" line ?   if not - it should...   

[Lightning]

with him running a RB, wouldn't a 1/2" line be better for it, so the pump can pump where it's supposed to?

[firefighter3931]

Nuthin wrong with a 5/16in line.  I know lots of guys running in the 11's and one well into the 10's with a factory (5/16) line and HV mechanical pump. 


Ron

[mikepmcs]

 

[Paul G]

does ur car have a 3/8" line ?   if not - it should...   

Yes it does. When I replaced the fuel pickup and sender unit in the tank it came in two sizes. I have the bigger one which I believe is 3/8".

[Rolling_Thunder]

with him running a RB, wouldn't a 1/2" line be better for it, so the pump can pump where it's supposed to?

generally it is not needed on most street cars -  the silver 69 charger in the shop is getting a 1/2" stainless line (that i have to bend   )  where as the black 69 got a 3/8" because he has only a mild 440....       the silver one has a 700+hp 496...