fuel questions

URDONE4

URDONE4

Club Member
my notch is having some fuel problems and i need them fixed asap so i can go to the track and actually spray on it. when i start the car up the fuel pressure gauge shows 7 pounds then as the car warms up and get driven a bit it will drop to 6, however, when i was on the highway today to go to wild woodys, i saw the gauge stay around 3.5 pounds then down to 2 pounds. after shutting the car off for about an hour, it way back to 7 pounds and then to 6 but didnt dive to 3 like earlier in the day. the car has a sumped tank, electric pump, and a 351w in it. i want to get it fixed so i can get a new baseline at the track before i fuck with the motor again this winter
 
Couple of things to consider.
1. Is your gas tank vented enough, if not, you could be causing a vacuum within the tank that is restricting fuel flow. Then, after you park it, normal pressure returns to the tank thru what ever vent you do have, and everything seems fine.

2. Remember that it is fuel volume that really matters, there just isnt an easy way to show volume on a guage, so we use psi instead.. Pressure is nothing more than a restriction to flow, if youre drivng on the expressway, using a higher volume of fuel, depending on the type of fuel system you have set up, youre guage may be seeing a drop in pressure because the needle seat assembly is open, allowing fuel into the carberator bowls. Less restriction to flow(open seat), less pressure shows on the guage. You need to check your system to see how much fuel its flowing.
 
strtracer said:
Couple of things to consider.
2. Remember that it is fuel volume that really matters, there just isnt an easy way to show volume on a guage, so we use psi instead.. Pressure is nothing more than a restriction to flow, if youre drivng on the expressway, using a higher volume of fuel, depending on the type of fuel system you have set up, youre guage may be seeing a drop in pressure because the needle seat assembly is open, allowing fuel into the carberator bowls. Less restriction to flow(open seat), less pressure shows on the guage. You need to check your system to see how much fuel its flowing.
Click to expand...


As that is correct.. If your lossing pressure at a higher RPM cruising.. You most def will lose pressure under load at wot and then throw the demand of flowing fuel for the nitrous..

The loss of pressure does come from not enough volume of fuel being moved by them pump vrs. the actual usage of the engine. Get a bigger pump! expecially if you plan to spray it.

Second, If you have dumps. check the pump location, hot exhuast gases blowing on the pump will greatly increas a pumps temp.. simple eletrics now.. Heat up a wire and its resistance goes up ..so same input less output due to power loss thru temp.. Heat the pump up the armature gets hot power is lost\cannot be created equaly due to the temp increase.. flow goes down .. systems then becomes inadaquite.
 
strtracer said:
Couple of things to consider.
1. Is your gas tank vented enough, if not, you could be causing a vacuum within the tank that is restricting fuel flow. Then, after you park it, normal pressure returns to the tank thru what ever vent you do have, and everything seems fine.

2. Remember that it is fuel volume that really matters, there just isnt an easy way to show volume on a guage, so we use psi instead.. Pressure is nothing more than a restriction to flow, if youre drivng on the expressway, using a higher volume of fuel, depending on the type of fuel system you have set up, youre guage may be seeing a drop in pressure because the needle seat assembly is open, allowing fuel into the carberator bowls. Less restriction to flow(open seat), less pressure shows on the guage. You need to check your system to see how much fuel its flowing.
Click to expand...

so to check that venting can i merely remove the gas cap and check the gauge while it is running?
 
What kind of pump, where is it mounted, and do you have a return line? Your needle and seat assembly can exhibit some of the problems you're mentioning, but that will typically always start at normal PSI, then just get lower and lower.
 
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