SOHC to OHV 4.0 Swap, PCM shutting off fuel pump/injectors

[gkorgood]

Hey all, long time lurker but just made an account to ask this, because I'm at a loss. Swapped my known good 4.0 OHV out of my crashed 2000 4x4 into a newly acquired 2002 FX4 which had a blown head gasket on its 4.0 SOHC (but ran *just* well enough to get it on and off a trailer). Both manuals, swapped PCM appropriately, using the 2002 body side connector to the 2000 engine harness. At first the starter wouldn't fire, we were able to ground the starter relay from where it was trying to get ground from the computer through the body to engine connector but the 2000 doesn't have that pin. We've confirmed we have crank and spark, and that the fuel pump and its relay work by jumping it directly. When key is in the run the fuel pump relay immediately clicks on and off (not the 2-3 second prime we're expecting, a rapid double click, on-off). We think the computer is shutting off the fuel pump, maybe because of something with PATS (the 02 has it, but the 2000 didn't) but we can't seem to confirm that or think of anything else it could be. Can't check OBD2 codes because the OBD system doesn't seem to be getting the right handshake to initiate, we think that might also be related to PATS. Any help you gurus can provide is greatly appreciated.