Fuel gauge / pump question
Thread Starter
Instructor
Joined: Sep 2000
Posts: 229
Likes: 3
From: NJ
Fuel gauge / pump question
So I am just about done with the installation of all Autometer analog gauges to replace the digital dash in my 88 coupe. The car also has an aftermarket external fuel pump installed.
Now, heres whats weird: I know the car has about 5 gals of gas in it, and the gauge reads about 1/4 with the car off. With the car in acc, the fuel pump starts and the gauge increases to about 1/3 full... then goes back down to 1/4 when the pump shuts off. When you crank the car and have it running, it reads just under 1/2 full.
I took the stock wire behind the dash for the fuel level sending unit. The guage is the correct 90 ohm that is used on GM cars.
Any ideas why this happens?
Thanks,
-JRW
Now, heres whats weird: I know the car has about 5 gals of gas in it, and the gauge reads about 1/4 with the car off. With the car in acc, the fuel pump starts and the gauge increases to about 1/3 full... then goes back down to 1/4 when the pump shuts off. When you crank the car and have it running, it reads just under 1/2 full.
I took the stock wire behind the dash for the fuel level sending unit. The guage is the correct 90 ohm that is used on GM cars.
Any ideas why this happens?
Thanks,
-JRW
Drifting
Joined: Apr 2008
Posts: 1,565
Likes: 2
From: Sparta Mo.
The gauge is correct, is the sender? My wifes car reads 1/4 when it's full and about 3/4 when it's empty. (it has a Mopar/Ford sender)
If it's the right sender, your return line might be right by the float. When the pump is squirting fuel back into the tank, it may be messing with the sender. There's a sump in the tank to keep the fuel by the pick up. If your pump is really pumping alot of fuel, it can't take it all and it's sending alot back to the tank. It may be filling up the sump area and not flowing back to the tank right away. When you shut off the pump the fuel level in the sump area goes down and the float returns to the actual fuel level.
If this is what's happening, just let it fly. You'll notice the sender will still work, but you're fuel level will drop like a stone from 3/8 to empty.
If it's the right sender, your return line might be right by the float. When the pump is squirting fuel back into the tank, it may be messing with the sender. There's a sump in the tank to keep the fuel by the pick up. If your pump is really pumping alot of fuel, it can't take it all and it's sending alot back to the tank. It may be filling up the sump area and not flowing back to the tank right away. When you shut off the pump the fuel level in the sump area goes down and the float returns to the actual fuel level.
If this is what's happening, just let it fly. You'll notice the sender will still work, but you're fuel level will drop like a stone from 3/8 to empty.
