Scotty I have a 99 Chevy express 3500 cargo van with the 350 vortec this is the second time this has…

Scotty I have a 99 Chevy express 3500 cargo van with the 350 vortec this is the second time this has been doing this it started about a month ago and wouldn’t run for 2ish weeks then ran for 3 days and it’s doing the same thing when turning over it will turn over then bang loud and shake the van then start grinding I have had the same code and it’s just a bad sensor so I know that’s not the problem I have fuel and spark “found that out the hard and painful way” have have tested the starter at my place and at the auto parts store works fine when not attached. Motor turns over by hand so it’s not locked up. And when it does start it runs just beautifully no knocks no ticks 490k miles.

Would love to figure this out and what is causing it even when connected to another battery and jumping this vehicle it does the exact same thing just a lot louder of a bang
https://www.themaven.net:443/api/media/289FE4ED-1763-4A61-86ED-566FF687E065

bang means raw gas it getting into the exhaust and then blowing up. Bad ignition systems, leaking fuel injectors, or internal engine wear like worn valves do that. From your description, check ignition and fuel first

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