well I checked all the grounds, removed them and wire brushed them, even switched the ECU with a 5.3 and did the VATS relearn, still no start.

I did find a plug that is unplugged, it is near the brake booster, its white with 2wires going to it, and its fairly long. It goes from near the brake booster to past the passenger side of the intake manifold. Anyone have an idea what it connects to? unfortunately I do not have a picture, but I did look on my friends 5.3 and he did not have the plug.

edit - nvm, I think the plug is for the underhood light.

I did take a log of it while it was cranking. Its showing my MAP is @ 100% when cranking. Swapped it out with a known good MAP sensor and still 100%. I will upload the log next. I also had the throttle wide open so the flames would come out the throttle body, otherwise there would be flames coming out the manifolds.

 

attached is the log. Anyone mind taking a look at it and seeing if anything looks out of the ordinary ?

I am thinking the timing could be off now, but I remember being precise with it when I did it. I followed the book to a T. The heads I had someone else put together, not sure if the rocker arms being torque over 22ft lbs can cause issues.

 

Last post for the night. I tinkered with it some more. Still no ideas. Could the rockers being too tight cause it to backfire through the intake ?

Cranking with throttle wide open = fire through intake.
Cranking with throttle closed = fire through exhaust and loud bang/ popping

Also - the SES light is on, but no codes are showing.

 

So I found some bad ground wires. Fixed those and she wanted to start. I got a feeling the timing may be off so I started pulling the front apart to get to the chain. Is it possible the crank is at 12 o'clock, but its not TDC ?

 

Did you do a cam swap on the 5.3? Or is it just a stock motor?

 

Yes, it has a LS6 cam in it (cam was free). Future plans are to boost it.