fuel pressure changes...

rod · 10-27-2011, 06:16 PM

i race my '56 Nomad at night races [at las vegas] and never get to see the fuel pressure gauge [dark]. last wed. night, i hit the shift just right to have the track lighting hit the outside gauge. it happened very quick, i watched the pressure drop from 8 to about 4 and then back to 8.
i had just cleaned the Holley blue pump vanes and internal screen, replaced the filter, and just put a new regulator diaphragm in. all the line is aluminuuuuuum or blue flex.
i don't know if this has been an on going problem, if it is new or just a fluke happening.
i wonder if it might have been the toggle switch doing something weird.

thoughts?
thanks rod in AZ

FED 387 · 10-27-2011, 07:44 PM

take the screen out and get a spring from Moroso to boost the pressure might solve your problem----now pressure and fuel volume are 2 different things so if it runs OK at both pressures maybe no need to worry bout it

rod · 10-27-2011, 11:19 PM

changing to other parts might change things but not correct the original problem. and that serves no purpose.
thanks for the suggestions however.
rod in AZ

Lew Silverman · 10-27-2011, 11:49 PM

Rod,

Was there a reason you serviced the pump? Had you experienced a fuel delivery issue prior to replacing the parts in the pump? What I'm guessing is that you might want to get a bulb for the gauge so you can get a better idea of what the fuel pressure is actually doing. If it starts at 8 PSI drops to 4 PSI under load and returns to 8 PSI, there may be a pressure drop when the demand is highest, but you're going to need to see the whole run!

Lew

rod · 10-30-2011, 02:05 PM

i have thought a light for the gauge. the thing is, i have used this fuel system for years, trouble free. so.....
i checked everything simply as a preventative. maybe i caused myself problems.
i run pump gas [i could get this thing to 'ping' i i had to] but as you know this new pump gas is very hard on rubber, when the gas sets in contact with rubber for long periods of time.
thanks for the comment.
rod in AZ

Adger Smith · 10-30-2011, 04:12 PM

Quote"changing to other parts might change things but not correct the original problem. and that serves no purpose.
thanks for the suggestions however.
rod in AZ" End Quote
Rod,
What he was trying to tell you was those two areas of that type fuel pump could be a problem. He wasn't trying to just have you throw a parts change at it. You might have just thought you weren't having problems before or you have picked up your program to a point where the fuel delivery "IS" a problem.
1. The screens restrict flow volume and can cause air to get mixed with the fuel. Air plays heck with regulators, Needle/Seats & emulsion tubes in the carb.
2. The pump pressure needs to be higher(with Moroso spring) because when you are leaving the line or pulling a gear change the fuel in the line sees more negative g forces and the pump needs to push harder to get the fuel to flow forward to the regulator. This could be your real problem. You have to think of the fuel in the line going forward from the rear to the front as a solid and understand how G forces apply to it. The pump needs to be putting out at least 14-18 lbs (some will say more) to keep the fuel going forward to the regulator in a real hard running car.
If you suspect the switch or electical is a problem just wire in your digital multi meter to the pump and monitor the voltage to the pump during a run.
Don't be too quick to dismiss the ideas or suggestions of someone with many years of experience.

rod · 10-31-2011, 11:22 PM

lew and adger. i was a bit quick, sorry. i need to change my thinking
rod in AZ

Adger Smith · 11-01-2011, 12:12 AM

It was Dick, too (FED)
Your welcome.
Hope you can pick up your ride a little... :~)

10-27-2011, 06:16 PM	#1
rod Member Join Date: Dec 2009 Location: Kingman, NW AZ. in the middle of the longest stretch of Route 66 Posts: 314 Likes: 0 Liked 20 Times in 15 Posts	fuel pressure changes... i race my '56 Nomad at night races [at las vegas] and never get to see the fuel pressure gauge [dark]. last wed. night, i hit the shift just right to have the track lighting hit the outside gauge. it happened very quick, i watched the pressure drop from 8 to about 4 and then back to 8. i had just cleaned the Holley blue pump vanes and internal screen, replaced the filter, and just put a new regulator diaphragm in. all the line is aluminuuuuuum or blue flex. i don't know if this has been an on going problem, if it is new or just a fluke happening. i wonder if it might have been the toggle switch doing something weird. thoughts? thanks rod in AZ

10-27-2011, 07:44 PM	#2
FED 387 VIP Member Join Date: Jun 2006 Posts: 3,416 Likes: 522 Liked 330 Times in 178 Posts	Re: fuel pressure changes... take the screen out and get a spring from Moroso to boost the pressure might solve your problem----now pressure and fuel volume are 2 different things so if it runs OK at both pressures maybe no need to worry bout it

10-27-2011, 11:19 PM	#3
rod Member Join Date: Dec 2009 Location: Kingman, NW AZ. in the middle of the longest stretch of Route 66 Posts: 314 Likes: 0 Liked 20 Times in 15 Posts	Re: fuel pressure changes... changing to other parts might change things but not correct the original problem. and that serves no purpose. thanks for the suggestions however. rod in AZ

10-27-2011, 11:49 PM	#4
Lew Silverman VIP Member Join Date: Mar 2010 Location: Newport News, VA Posts: 1,435 Likes: 371 Liked 129 Times in 59 Posts	Re: fuel pressure changes... Rod, Was there a reason you serviced the pump? Had you experienced a fuel delivery issue prior to replacing the parts in the pump? What I'm guessing is that you might want to get a bulb for the gauge so you can get a better idea of what the fuel pressure is actually doing. If it starts at 8 PSI drops to 4 PSI under load and returns to 8 PSI, there may be a pressure drop when the demand is highest, but you're going to need to see the whole run! Lew __________________ Lew Silverman #2070 "The Wagon Master" N/SA

10-30-2011, 02:05 PM	#5
rod Member Join Date: Dec 2009 Location: Kingman, NW AZ. in the middle of the longest stretch of Route 66 Posts: 314 Likes: 0 Liked 20 Times in 15 Posts	Re: fuel pressure changes... i have thought a light for the gauge. the thing is, i have used this fuel system for years, trouble free. so..... i checked everything simply as a preventative. maybe i caused myself problems. i run pump gas [i could get this thing to 'ping' i i had to] but as you know this new pump gas is very hard on rubber, when the gas sets in contact with rubber for long periods of time. thanks for the comment. rod in AZ

10-30-2011, 04:12 PM	#6
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: fuel pressure changes... Quote"changing to other parts might change things but not correct the original problem. and that serves no purpose. thanks for the suggestions however. rod in AZ" End Quote Rod, What he was trying to tell you was those two areas of that type fuel pump could be a problem. He wasn't trying to just have you throw a parts change at it. You might have just thought you weren't having problems before or you have picked up your program to a point where the fuel delivery "IS" a problem. 1. The screens restrict flow volume and can cause air to get mixed with the fuel. Air plays heck with regulators, Needle/Seats & emulsion tubes in the carb. 2. The pump pressure needs to be higher(with Moroso spring) because when you are leaving the line or pulling a gear change the fuel in the line sees more negative g forces and the pump needs to push harder to get the fuel to flow forward to the regulator. This could be your real problem. You have to think of the fuel in the line going forward from the rear to the front as a solid and understand how G forces apply to it. The pump needs to be putting out at least 14-18 lbs (some will say more) to keep the fuel going forward to the regulator in a real hard running car. If you suspect the switch or electical is a problem just wire in your digital multi meter to the pump and monitor the voltage to the pump during a run. Don't be too quick to dismiss the ideas or suggestions of someone with many years of experience. __________________ Adger Smith (Former SS) Last edited by Adger Smith; 10-30-2011 at 04:19 PM. Reason: sp

10-31-2011, 11:22 PM	#7
rod Member Join Date: Dec 2009 Location: Kingman, NW AZ. in the middle of the longest stretch of Route 66 Posts: 314 Likes: 0 Liked 20 Times in 15 Posts	Re: fuel pressure changes... lew and adger. i was a bit quick, sorry. i need to change my thinking rod in AZ

11-01-2011, 12:12 AM	#8
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: fuel pressure changes... It was Dick, too (FED) Your welcome. Hope you can pick up your ride a little... :~) __________________ Adger Smith (Former SS)