Each fuel pump assembly has a valve that prevents fuel from being pumped into the wrong tank. You can't just change the valve, the whole fuel pump assembly must be changed. The tank receiving the fuel when it shouldn't has the bad assembly, so you need to change the front pump assembly.

 

i didnt change the front fuel pump. i changed the rear. are you talking about the seletor valve?

 

i think you don't have a selector valve, you have 2 valves in each pump assembly. The fuel return valve is opened by the pressure the pump creates and should be closed when the pump is off. If it's not completely closed with pump off, fuel is retutning to both tanks at the same time, causing overfilling of unselected tank.

 

so how do i fix that? because i really wanna use both tanks, because im going into the desert to go dirt biking soon.

 

These valves are located at the top of plastic fuel pump shield, and it's impossible to get them out to clean/replace them. You may replace only that plastic shield in the front tank (if available w/o a pump) , or you may replace the whole assembly.

 

so this means i have to replace the front pump?

 

You have to replace the front fuel pump assembly. You may also want to save the old pump motor in case you'll need one in the future.

 

well i found out that the rear pump that i pulled out still works. the whole reason the pumps didnt work was because of a bad relay so since the old pump still works, should i take the the new fuel pump out and put it in the front, or should i put the old pump in the front tank?

 

If you're talking about your cross filling problem - not quite like that. If I remember it right, fuel pump assemblies have different plugs, so they're not interchangeable (but the pump motors are). It's not the pump's fault that you have this problem, it's all about check valves located somewhere under the plug inside of the top part (cap?) of fuel pump assembly. So you need to replace the plastic top of the assembly (not sold separately) to make fuel-back part of the system work right again. Or, if it's possible, wait until Monday, I hope to finally conduct the experiment on cleaning these valves with different chemicals this weekend (I also need to find a fuel pressure measuring tool to make sure it was successful, which is not very simple thing to do in here).

 

thanks for all your help man. I'm a total noob to working on trucks. so the check valve is in the fuel pump assembly? and a bad check valve causes cross filling? and the front and rear pumps are not interchangeable, because of the electrical plug? what causes the check valve to get stuck or go bad?