problem need help

i put a ls1 out of a 98 corvette. i got it from a guy that had it in a 57 Chevy. it came with a stand alone harness and the original comp. when i start it it runs for a couple seconds and shuts down. im getting a code for anti theft. the guy before must have had the vats bypassed some how and was wondering what i have to do to fix this problem im stumped and any help will be good.

If it fires and dies immediately thena it's most likely a vats issue which would need to be dealt with by a tune

thats what it dose but it ran in that 57

check fuel pressure while firing the truck, see if the fuel pressure maintains as it dies. Also, check the voltage going to the pump and see if the voltage drops at the same time it dies.

yea i checked that it maintains voltage and pressure i thought it was a fuel problem cuz it was shutting down so i wired it to the ignition.

alot was tuned out of the pcm but im getting codes for evap anti theft and coolant temp the temp sensor has no wireing in the harness so it wasn't tuned properly

then you still have anti theft on the computer. eliminate it all and u should be good to go.

When vats cutts off fuel, its shuts down the injectors. I was just trying to eliminate the fuel pressure being an issue. Gonna be a tough one to diag over this if it is not vats.
just make sure theres not vats still on the comp. thats what it sounds like it is.

thanks ill have to call nelson tommarow

good choice on getting a tuned PCM with the VATS turned off. NP will do a hotrod tune for a very good price. Tell them what you want turned off like rear 02s and they'll take care of it. Later, if you want a real tune they will discount the price of the full tune. Just go for the full blown tune and be done with it and you get lifetime updates as long as you don't go full on rediculous with engine mods like FI.