5.3 swap ran but now no spark/start issue
 

My 5.3 swap went fine, I have had it running and driving in the driveway. Did a little paint work on the rear frame and pulled it back in the shop. It stopped running, now it has a no start issue. No check engine light at start like it used to, it cranks but has no spark. I have fuel at the rail and sprayed starting fluid in the manifold still no start. Pulled plug confirmed no spark. Brand new PSI harness and computer were used. 12+ volts at the battery, drops to 10.5 voltage when cranking. Where else to look?

Re: lq4 swap ran but now no spark/start issue
 

Check to make sure all your fuses are good and also check to make sure all your grounds are clean and tight. Sounds like wiring issue to me and these are the two main culprits.

Re: lq4 swap ran but now no spark/start issue
 

Can you confirm you're seeing 10.5v or better at the pink IGN trigger line going to the ECM? The one that tells it the car is ON (as opposed to the main battery connection)?

Re: lq4 swap ran but now no spark/start issue
 

Turns out the ground on the cylinder head was a tiny bit loose. I checked them all over and over but just a half turn on the bolt and she fired right up again. Crazy how finicky it is. Also found out my front headlight harness is crap as well. Gotta love these things.

Re: lq4 swap ran but now no spark/start issue
 

The simplest things sometimes...Glad you got it sorted out.