A little background...03 5.3 put in a 70 C10 using stock harness and fuse block for wiring. The motor was started and has run a dozen times in my shop while moving around and driven in parking lot. Last week I got it out and drove it around the parking lot at the shop...couple of donuts later and I pull it back in for some paint work. Everything was running fine when parked. Next day or two, fire the truck up to move and its running rough, like a misfire. This occured the next couple of times that it ran, and this week it won't hit a lick. Scanned today with HPtuners with no real results. No DTC's, all readings that are present while not running are there and not abnormal. I have pulled the plug wires and I'm getting spark, I pulled the fuel rail and witnessed fuel injector spray on all 8 injectors with a healthy fan of spray. Fuel pressure is at 58 constant...on and on. Any ideas would be greatly appreciated.

 

Compression?

 

Getting spark on all 8 cylinders ?

 

the above events described are as far as we got yesterday. I checked 1 plug wire on either side for spark but didn't check the other 6. One suggestion has been severely fouled plugs not letting if fire. They are the plugs that came with the motor which were on the list to change out, just not on the top of the list. I will change them next and see what happens. Its just weird that it was running fine, running rough, not running, and no codes. Thanks for the replies

 

Probably no help, but it sounds like it's flooded.

 

I didn't notice that ↑ before, I guess I am Captain Obvious now.

 

Look at tps voltage. If its high and your not giving it gas, it won't start.