Q: Installed mew battery in 06 trailblazer now it wont start it cranks but wont start

This may be related to many different possibilities, some of which may be related to a lack of spark or possibly timing issues and some of which may be related to a fuel delivery problem or a combination of both. Things like ignition coils, crankshaft position sensor, spark plugs, spark plug wires or ignition module are all components that help to create spark and control ignition timing which may cause the motor to not produce spark or the correct timing needed to ignite the fuel in the motor.

In the case of a fuel delivery problem, this may be related to low fuel pressure, faulty or dirty fuel injectors, a faulty or dirty idle air control valve (this relays information about air intake to the computer which makes fuel adjustments), or potentially a faulty fuel pressure regulator or fuel pump. Fuel delivery problems will typically not allow the proper amount of fuel to be delivered to the cylinders which results in a lean fuel condition which can cause backfiring or simply cause the motor not to start as a result of fuel starvation. In some cases too much fuel may be supplied to the motor causing too much fuel to be introduced to the motor faster than what it can burn it. This results in the motor being flooded with too much fuel also causing it not to run properly. Any of the above possibilities can create an imbalance in the proper air/fuel ratio as well which will cause the motor to run very rough or not at all. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.