I have a 1988 Chevrolet 3500 with a 454 and when you switch from left tank to right tank truck engine leans out...i have personally changed both pumps ( 1 in each tank) i have changed the switch valve and the switch in the cab, new lines from tanks to switch valve and for the heck of it i just changed the right tank pump again. The reason i know it leaning out cause you can hear the difference in the motor when switching and while watching my scanner i can see block learn(145) going up and the integrator staying low(128) on the right tank and the block learn and integrator matching on the left tank.....any ideas?
I'd take a look at the grounds for the pumps. If one of them is a little loose or dirty, it will affect the pump's ability to work correctly.
Good Luck and God Bless
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