Right fuel tank fills left tank

[srfinatsunset]

I have a 1980 c3500 with dual tanks I just put in new fuel sending units and hoses. Now with the motor running fuel from the right tank it goes to the left tank. The hoses are hook up probably. What would cause this problem. How do I fix it?

 

[da_raabi]

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[Iowan]

I haven't ever had an aux. tank but could the pump be reverse flow? Shot in the dark. Sorry I couldn't be more help.

 

[srfinatsunset]

The problem was pinched fuel line at the sending unit. When I put in new units I didn’t remove the bed. Well I left the fuel lines too long.

 

[highdesertrange]

the return lines are crossed? do you have return lines? highdesertranger