The fuel injectors may need to be cleaned and even the fuel rail. Fuel pressure regulator could also be a problem.
You need to let us know what year your truck is and if you have no spark, start from there to troubleshoot, might be the ignition module
Looking for a Used Blazer in your area?
CarGurus has 1,349 nationwide Blazer listings starting at $1,995.
Search Chevrolet Blazer Questions
Chevrolet Blazer Experts