Rebuilt engine wont run. Has compression, Spark and fuel?

[blades11b]

I've seen many threads on LS1 tech about having the coil assemblies on the incorrect side and it running like shit. Try it out to rule it out.

For sure. I do believe some of the early LS's did have the wiring different so that the coil packs were actually only meant for one side. These however are the same PN and wired the exact same. (I had them off to check the circuits) but to be sure I did try switching sides and made no difference. Also keep in mind that like I said, there are scenarios when it will actually run.

[blindsquirrel]

Actually a further detail, instead of just key-on while measuring voltage drop, the coils should be firing, meaning check it while cranking. It maybe isn't obvious but the less current being pushed through what you're measuring, the less of a voltage drop you will measure. This is exactly like plumbing just with electrons instead of water. Voltage drop = pressure drop. If you measure a pressure drop in one section of plumbing, you have found a restriction.

Have you tried the quick-n-dirty, adding +12v straight from BAT+ term and GND straight from BAT- term to the +/- wires in the coil harness? That's a good first step before checking voltage drop, as if you can bypass a part of the harness and it suddenly works, then you know there is a problem there that can be pinpointed with further checks like voltage drop.