I put 5 stock ecu in my previous rebuilted motor and can't get the fuel pump to prime. Here where it gets weird, the fuel pump will prime using a PFC. So what do you think could happen?

 

Any ideas why the stock ecu wouldn't prime the FP and the PFC will?

 

I guess I got one of those problem nobody ever had or heard of?

 

Check the plugs on your crank angle sensors and if you haven't yet jump your fuel pump 2 make shore it works .

 

Could also be a Relay or fuses.

 

Do you have a pressure gauge on your fuel line?
If not you need to get one to confirm that "priming" is the problem.
Cold start "priming" is not a common problem in August.

If you jumper the fuel pump (use the test plug by the battery), does it pressurize the system. If not then you probably have a bad fuel pump or pump wiring.

If you then remove the test jumper does the pressure drop rapidly?
If so then you may have leaking injectors or the pump is not holding pressure (bad o ring in the pumps outlet connection).

Cold start fuel enrichment (aka priming) has to be tuned on the PFC. I don't think that this is your problem in Kansas in August.

I don't think that the PFC manages the turn on of the pump any differently than the stock ECU. The pump does not turn on until the starter is engaged.
If the system holds zero pressure once the pump is turned off then you have to crank the engine until the pump can pressurize the system.