Is there any way to tell if both fuel pumps are actually working? Such as datalogging? If so what PID's would show what I am looking for and what values should they be?
If either fpdm is unplugged the engine should still keep running, correct? My engine idles with 39 psi with the original fpdm (#1) unplugged and the GT500 fpdm (#2) plugged in. However, if I keep #1 fpdm plugged in and unplug #2, zero fuel pressure and the engine dies. I switched the fpdms around and it does the same. With Both #1 & #2 plugged in I measure 12v at the tank connections. My guess is a Dead pump?
Update:
One pump was dead. Wires were fine, there was power at the fuel pump connector for both pumps all along. Replaced the harness anyway and the pumps last night.
Now the sct x3 shows a FPDC of .18 at idle. Did a massive burnout and it never went over a .20 FPDC reading. Right where it should be.
Tip for the sct owners out there: the xcal3 reads FPDC/2. So the reading you get on your tuner is 1/2 of what it actually is. A .18 is really 36%.