Help diagnosing CEL 0042

[sapper12b]

So I have not been able to drive due to medical issues for a while so I decided to tear into the ole girl. Before I started she ran just fine, no CEL, one minor leak. The mods I did on the motor are as follows:

FP Manifold
Evo3 O2 housing
3" exhaust
Revised lifters
Speed density setup( was running GM maf/maft)
Took off intake manifold to tap for map sensor
Aluminum radiator
Quick disconnect injector clips
FMIC
ECM link v3 lite
I went to start it up and for one my battery was pretty dead, but it eventually fired up. It ran on its own, but threw that code. I let it run for maybe 1 minute and shut it off to research the CEL and didn't find much. I know the ecu is good as I just got it back from the guys and ecm tuning not long ago. I need to know what I should test first, I am kinda lost. Still learning these DSM as I go. Any help is great.

 

[Rs AWD]

fuel pump.. i think that means the fuel pump isn't seeing a consistent 12V for the most part. do you have an aftermarket fuel pump or at least a re-wire kit? maybe the battery was dead for to long and isn't charged all the way.