What portion of the tune is the secondary fuel pump control controlled by? I have a 1998 3500 that I added a secondary tank to. It is running on a 411 pcm with an express van base tune. I swapped in the fuel segment from a 2001 suburban that had dual tanks. I was able to get the gas gauge to read the proper level between the two tanks, but I can't get the pcm to trigger the secondary fuel pump relay.