So its kind of a long story I'll condense to the basics:
1994 S10 LS Swap with a Current Performance Wiring harness
2004 P59 Van ecm w/DBC/IAC controls

This truck has been swapped for 7 years. Originally it was a 5.3/4l60e. Over time things changed. This year I swapped to a 4l80e. I tried to segment swap my old ecm, and it bricked. When it did I swapped to a P59. I had to move some wires as well as add some grounds (could be issue #1) When the 4l80e was swapped in, the original harness was not made long enough for the vss to reach. My fix, was to dismantle a factory harness and add in the new vss/ turbine speed sensor from the van harness, so nothing has been cut, spliced or otherwise hacked up. Also a relay was added, which was jumped off a existing relay for a trans cooling fan. The fan shuts off when the truck is powered down like it should.

At this point the truck starts/runs drives as it should. If the truck sits somewhere between 1 and 2 days, it is somewhere between almost dead, to totally dead. I have used a test light to try and narrow down what is going on here and the best I can tell it is the ecm. I have checked all of the 12v+ sources and the Key on 12v+ sources and they all seem to be in the correct spots and doing what they should. So far, I disconnected just the ecm 1 night and the battery was fine the next day. I am going to look to see if I can get this to continue over a couple of days or maybe 3 this holiday week and see how it goes.

Has anyone had any issues with a ecm causing a parastatic draw like this? I can not find any info in the internet other than guys having their 12v+ and the 12V+ key on mixed up. I am wondering if possibly a segment flash may help fix this issue? I am also going to try to borrow a different ecm to just hook up, to see if the issue continues. ANY info is appreciated!

 

Start by measuring your current draw on the various circuits and you will have your answer because everybody else is just going to be guessing. A segment swap isn't going to cause your PCM to draw more current.

 

O Reilly rents a tool called Amphound
it really helps finding problems like this

 

I have tried to narrow down where the draw was specifically, however pulling out the fuses did nothing. I had everything out and still had the issue. One problem I have is I can't get a diagram from current performance as that's " proprietary information"
I did not mean to illude a segment swap would cause the issue, more to the effect if the ecm wasn't going to sleep, if perhaps a segment swap may fix it is all.

 

Just to update this thread, I did narrow this down to a bad ecm. I do not know what the problem is in it, but I do know it is in the blue connector. If I disconnect it, the drain goes away. I ended up swapping in a 2005 p59 I had, and it seems fine now. Strange, and a real pia to troubleshoot!