Skeene

Hey I have a 2003 chevy Silverado with a 6.0 in it. Im having issues im needing some help with I cant figure it out. It sat up for a few months, It cranked right up and ran very rough, spitting and sputtering, I only cranked it to move it. Then a few months later I go to crank it again and it would turn over but wouldn't even try to fire off. So I drained all the fuel, changed the fuel filter and put fresh fuel in it. It still would only turn over and not even try to start. So then I checked the fuel psi, it was a steady 58psi. I changed the crank sensor and the camshaft sensor, I had a nelson tuned computer in it, and I put the factory computer back in it, nothing same thing. I then put the Nelson tune pcm back in it. Now as soon as it starts turning over it backfires out the exhaust extremely loud one time then continues turning over without starting. No codes. Took the valve covers off, all looks good, checked fuses and the coils and harness all looks good. Anyone got any suggestions??

Thanks,

bbond105

Check the grounds on the back of the heads.

izaks

The harness for the coils sound like they have been reversed. (cylinders not firing in the correct order)
Try switching the harness around that plugs into the coils

Skeene

But the harness has never been unplugged.

sowbelle

clogged injectors
rodents

andy burdess

Check spark plugs