My buddies 88 FC is having a starting issue after a motor swap. The original S4 block was going bad so we put a used S5 block in better condition. Everything on the block is S4 from the original motor except for some headers.

The motor cranks fine, has spark, but the fuel pump isn't activating with the ignition key for some reason? However if you jump the 2-pin yellow check connector to prime the fuel system the pump turns on. I pulled off the pressure line after the fuel filter to confirm its pumping fuel to the rail but there is nothing coming back through the return line. Is this normal? I tested the main relay and checked fuses.

So basically the issues are: Ignition isn't activating the fuel pump so it wont start and there is no fuel returning via the return line.

Help, suggestions appreciated folks

 

If the car is not running then "normally" you have to turn the key to start to turn the pump on. Key to on and engine not running will not in itself turn the pump on. You would either have to jump the connector or physically push open the AFM flap to trick the pump to turn on w/key to on and engine not running.