Question on loosing fuel pressure going down track.

Jeff Stout · 01-20-2020, 06:13 PM

With a quality gauge mounted in front of me on windshield I can watch fuel pressure going down track. What is happening is the pressure is going from 6 lbs to 3.5 lbs. at finish line. I do NOT have a return. I used a good quality pump (dont remember what name brand is in this car) with -8 up to regulator and -8 from reg to carb. My thought is I need a jetted -4 return line at regulator so I can adjust regulator and maintain 6 lbs at finish line. I have plenty of -4 line and would need to only buy fitting that holds jet and my time to run it in car.
Would this help the problem or 3.5 lbs. is enough for a slow car?

Bobby DiDomenico · 01-20-2020, 06:59 PM

Main thing is to keep the bowl full enough so the jets are covered. What car/carb?

Kenny Wigington · 01-20-2020, 07:07 PM

You may be having a voltage drop issue. The bigger the feed wire, the better, and closer to the battery, The better you will be. Double check your ground connections, to the pump and relay, too. 10 gauge to pump, at minimum, and 8 would be even better.
If you have a good meter, try to read the voltage, thru the relay, it might show you a problem there.

Jim Wahl · 01-20-2020, 07:13 PM

Quote:

Originally Posted by Kenny Wigington

You may be having a voltage drop issue. The bigger the feed wire, the better, and closer to the battery, The better you will be. Double check your ground connections, to the pump and relay, too. 10 gauge to pump, at minimum, and 8 would be even better.
If you have a good meter, try to read the voltage, thru the relay, it might show you a problem there.

Either this or your old pump is just worn out! Jim

.

Chevy55 · 01-20-2020, 09:20 PM

From Areomotive

At the track, from the launch to mid-track, fuel pressure is steady, but then down track, it falls 2 PSI or more, what’s wrong?

The first thing to be blamed is usually the regulator, but in fact this is a strong indication of a fuel supply problem. If for some reason there is insufficient volume available from the fuel pump to feed the engine, fuel line pressure can drop to the carburetor. Even with a static regulator, a significant drop in line pressure affects flow through the regulator, causing regulator pressure to drop. Do not automatically assume the pump is bad or inadequate, inspect and resolve any supply line issues to the pump, ensure the tank is vented and the vent is functioning, and be sure to check the fuel pump wiring, along with the overall electrical system performance. Finally, if you still have problems, contact Aeromotive for a proper flow test you can perform in the field to verify if your fuel pump is performing properly.

jim morgan · 01-20-2020, 09:38 PM

Or maybe you don’t have a problem, Before all this high pressure,high volume systems
I had a max wedge , Carter electric and manual pump had 6 pounds thru the lights at 2 pounds went 127.5 mph that’s 30 years ago, is your car nosing over, ?

Jeff Stout · 01-20-2020, 10:08 PM

Quote:

Originally Posted by Bobby DiDomenico

Main thing is to keep the bowl full enough so the jets are covered. What car/carb?

Olds 307 large q jet

Jeff Stout · 01-20-2020, 10:11 PM

Quote:

Originally Posted by jim morgan

Or maybe you don’t have a problem, Before all this high pressure,high volume systems
I had a max wedge , Carter electric and manual pump had 6 pounds thru the lights at 2 pounds went 127.5 mph that’s 30 years ago, is your car nosing over, ?

With it being a fairly new combo to me. My opinion is that it is not nosing over as the mph matches the et. Side note is the o2is going from 13.5 to 11 in high gear.

Greg Hill · 01-20-2020, 11:17 PM

What brand of pump do you have? A q-jet is notorious for being hard to keep supplied with fuel. When I built my car it had a 780 Holley and I was using a Mallory 140 pump and a 3/8 fuel line from the tank to the regulator and everything worked great. When I switched to a q-jet combination I ended up switching to a Barry Grant 280 pump and a 1/2 inch line from the tank to the regulator to get it to run right. The amount of fuel to a q-jet is critical.

Alan Nyhus · 01-21-2020, 07:59 AM

Take the line off at the carb, run the fuel pump for a full minute and measure the volume it pumps. Do this with the gas cap on and off to see if there's a difference. -Al

01-20-2020, 06:13 PM	#1
Jeff Stout VIP Member Join Date: Dec 2001 Location: phoenix Posts: 1,407 Likes: 53 Liked 654 Times in 254 Posts	Question on loosing fuel pressure going down track. With a quality gauge mounted in front of me on windshield I can watch fuel pressure going down track. What is happening is the pressure is going from 6 lbs to 3.5 lbs. at finish line. I do NOT have a return. I used a good quality pump (dont remember what name brand is in this car) with -8 up to regulator and -8 from reg to carb. My thought is I need a jetted -4 return line at regulator so I can adjust regulator and maintain 6 lbs at finish line. I have plenty of -4 line and would need to only buy fitting that holds jet and my time to run it in car. Would this help the problem or 3.5 lbs. is enough for a slow car?

01-20-2020, 06:59 PM	#2
Bobby DiDomenico Senior Member Join Date: Jun 2002 Posts: 907 Likes: 85 Liked 88 Times in 45 Posts	Re: Question on loosing fuel pressure going down track. Main thing is to keep the bowl full enough so the jets are covered. What car/carb?

01-20-2020, 07:07 PM	#3
Kenny Wigington Senior Member Join Date: Sep 2004 Location: Cumming,Ga. USA Posts: 967 Likes: 36 Liked 60 Times in 12 Posts	Re: Question on loosing fuel pressure going down track. You may be having a voltage drop issue. The bigger the feed wire, the better, and closer to the battery, The better you will be. Double check your ground connections, to the pump and relay, too. 10 gauge to pump, at minimum, and 8 would be even better. If you have a good meter, try to read the voltage, thru the relay, it might show you a problem there. __________________ 2894 STK

01-20-2020, 09:20 PM	#5
Chevy55 Member Join Date: Nov 2014 Posts: 304 Likes: 606 Liked 167 Times in 83 Posts	Re: Question on loosing fuel pressure going down track. From Areomotive At the track, from the launch to mid-track, fuel pressure is steady, but then down track, it falls 2 PSI or more, what’s wrong? The first thing to be blamed is usually the regulator, but in fact this is a strong indication of a fuel supply problem. If for some reason there is insufficient volume available from the fuel pump to feed the engine, fuel line pressure can drop to the carburetor. Even with a static regulator, a significant drop in line pressure affects flow through the regulator, causing regulator pressure to drop. Do not automatically assume the pump is bad or inadequate, inspect and resolve any supply line issues to the pump, ensure the tank is vented and the vent is functioning, and be sure to check the fuel pump wiring, along with the overall electrical system performance. Finally, if you still have problems, contact Aeromotive for a proper flow test you can perform in the field to verify if your fuel pump is performing properly.

01-20-2020, 09:38 PM	#6
jim morgan Member Join Date: Dec 2003 Location: Wilson NC Posts: 105 Likes: 281 Liked 51 Times in 8 Posts	Re: Question on loosing fuel pressure going down track. Or maybe you don’t have a problem, Before all this high pressure,high volume systems I had a max wedge , Carter electric and manual pump had 6 pounds thru the lights at 2 pounds went 127.5 mph that’s 30 years ago, is your car nosing over, ? __________________ Jim Morgan 1916 , 9916 STK

01-20-2020, 11:17 PM	#9
Greg Hill VIP Member Join Date: May 2006 Location: Louisville , KY Posts: 1,994 Likes: 63 Liked 270 Times in 68 Posts	Re: Question on loosing fuel pressure going down track. What brand of pump do you have? A q-jet is notorious for being hard to keep supplied with fuel. When I built my car it had a 780 Holley and I was using a Mallory 140 pump and a 3/8 fuel line from the tank to the regulator and everything worked great. When I switched to a q-jet combination I ended up switching to a Barry Grant 280 pump and a 1/2 inch line from the tank to the regulator to get it to run right. The amount of fuel to a q-jet is critical. __________________ Greg Hill 4171 STK

01-21-2020, 07:59 AM	#10
Alan Nyhus VIP Member Join Date: Dec 2002 Location: Lower Dakota territory Posts: 1,163 Likes: 1,013 Liked 761 Times in 225 Posts	Re: Question on loosing fuel pressure going down track. Take the line off at the carb, run the fuel pump for a full minute and measure the volume it pumps. Do this with the gas cap on and off to see if there's a difference. -Al __________________ "That'll never work....."