So I just recently had to put a 1991 dodge d150 fuel tank in my 1988 dodge d100 and I had to replace the fuel pump with an aftermarket one in the fuel tank but my fuel gauge is all over the place. I can fill it up and it will show full but when I drive it 10 miles down the road and kill the truck and crank it back up it’s showing 3/4 of a tank and the within 3 days my fuel gauge is showing empty but i have only driven like 50 miles on that full tank and I have been filling it up every 200 miles and it is just right there I normally have about 5 gallons left in my tank by then. Any suggestions? Could it be because it’s a newer style fuel pump? I don’t know if the fuel gauge was right when I had the oem fuel tank and pump in because I had just bought the truck but tank had a huge crack in it so I never drove it until I put the new tank in.

 

Did you replace just the pump, or was it a complete module? (gauge stuff included....)

 

The fuel pump and sending unit is all one piece for the 91 fuel tank so I replace the whole thing it even had the float to tell you the fuel level I’m thinking either I got a bad fuel pump or the gauge itself is messed up or it’s something to do with the newer pump connected to the older gauge

 

Test the gauge. See what happens. What brand fuel pump did you get?

 

I will test the gauge when I have the time to but the brand fuel pump I used was “Airtex”

 

Airtex? Well then.... I think you just found your problem. They are NOTORIOUS for putting out crap parts. I won't use them. At all. Ever. I will wait a week from some other brand before I would install an AirTex pump.

 

thank you so much I’ll look into different pumps and see which one is gonna be best for me I wish they still mad mopar fuel pumps but I can’t find them anywhere

 

so did you replace just the fuel pump or the whole assembly? if you got the old fuel pump assembly you can pull the old gauge sending unit off the old sending unit and bolt it to the new pump assembly and test it with the gauge.

 

And don't even have to drop the tank..... unplug the current pump, plug in the old one (outside the tank, turn the ignition on, and move the float up and down, while someone watches the gauge. See if it does what it's supposed to.