Generation III External Engine - put headers on car wont run

after installing the headers and high flow cats i turn the key it doesnt seem to want to fire right away gotta hold the key for a couple second i looked over all the coil packs, spark plugs, ground wire to the motor,starter wires,02 censors,alternator,battery,fuses.when i turn the key itll turn over and fire up for a second a die,i know im getting fuel and spark the exaust gets hot.Any ideas greatly appreciated

You seem to have covered the basics. Are you getting an SES light? If so, check the Codes. May give you a direction to look into.

coolant temp sensor

coolant temp sensor



It is easy to break if it is aged and the plastic housing is brittle.

Could also be the crank sensor if you knocked it off and didnt notice u did. That's been known to happen