1G Machinegun Backfiring

[Nightfall Talon]

What I have - 1992 6-bolt TSi 5-speed AWD Talon, mostly stocker. Engine is freshly built from the ground up, driven around the block twice. EGR removed, vacuum hose clean up done.

Problem - Under load (in gear driving), repetitive rapid backfiring, feels like lack of power.

What I've tested so far - Checked plugs, boost leak test. (Came up in the search as the most common issues)

What do you guys think?

 

[motomattx]

Try it with the mass air sensor unplugged without making a bunch of boost, it sounds like a fuel delivery issue, as in it sounds like its lean.