Two Fuel Pumps At Same Time ??

Current info: 1986 33' motorhome on P30 chassis with 454 Gen V engine and TBI system including OBD1 wiring harness installed from a 1993 C3500 HD. 1228747 ANRS ECM.


After two intank fuel pumps failed I installed a Carter P5001 external TBI pump and eliminated the intank pump using an extended pickup tube with strainer. I barely made it home from a ten mile road test. I watched fuel pressure drop from steady 12 to 8 or less PSI. It appeared that the fuel was overheating. The lines and pump were hot to the touch. Inline fuel filter was clean. I'm using 3/8" and 5/16" nylon pressure and return lines. Original supply line that fed mechanical pump to carb was 1/2". Might need to consider that? Now it looks like I have to remove the 60 gallon tank "again". New intank pump on the way.


My plan is to reinstall another new intank pump and use the Carter pump at the same time, if possible off the same relay. I welcome any comments related to what I'm about to do. thanks

UPDATE: New intank pump installed. Used seperate relay for external pump triggered by oem relay. Installed mehanical gauge inline between in tank pump and external pump just ahead of inline fuel filter. Both pumps run the required 2 seconds before startup.

Then after running for several minutes, the in cab electric gauge settled down to 12 psi. I crawled under and saw that the mechanical inline gauge stays at 0 psi. Maybe the rail pump pulls harder than the intank pump can build any pressure ??? Not sure about that !!!

Iv'e done a few short road tests, 10 miles total. All seems ok remaining between 11 & 13 psi. Finally settled down to a steady 12. Now I'm going to have to build up the courage to do a longer road test. Any thoughts on that pressure difference would be appreciated. thanks