Hello, I have a 1996 blazer and I just did the lower intake gasket on it. Put it all back together set the TDC and hanve it running but there is a knocking sounds now. Just wondering if it's a sensor that needs to be reset or something, any kind of help is appreciated. Thank you

Knocking is not good.
Is it deep inside engine?
Did the engine run with coolant in oil?
Coolant in oil will wipe out rod and main bearings.

Pull dip stick and see if oil has coolant in it.

On knocking noise remove one plug wire at a time with engine running and see if any change noise or remove noise.
If so rod bearing are shot.

Let us know what you find there.

It's putting a p0340 code

It's putting a p0340 code

Code 340 is a camshaft position sensor or wiring problem.

Check is cylinder for rod or piston noise by pulling plug wire while running.