i have a 98 blazer. 4.3 vortec the heads blew so i had the heads replaced by someone not a certified mechanic.. first mistake.. but there still is no compression.. it was reading 22 on the first cyclinder. and 25 on the next. not sure if the heads were put on wrong or what. what could cause this again.

 

Lots of things can cause loss of compression in a cylinder, all of which tend to be expensive:

Cracked head
Head gasket leak
Valves bent or burnt, seats not sealing
Cracked block
Cracked or burnt pistons
Broken or burnt piston rings

The time to diagnose the problem is before you tear it apart, with a cylinder leak-down test. Such a test won't always pin-point the exact problem, but it'll tell you which direction to look...ie whether the problem lies with the head/valves/gasket or with the piston/ring/cylinder wall.

You really haven't posted enough information to make an educated guess as to what the problem might be... although with two dead cylinders, I'd have probably opted to swap out the engine rather than just change a head.

Having work done by a "non-certified" mechanic doesn't necessarily mean much. I know lots of guys who are excellent mechanics but aren't ASE certified, mostly because their regular job is in a different field. I do quite a bit of my own work and I'm not ASE certified.

 

true about the mechanics..

well the heads where cracked and i had them replaced with all new gaskets etc the heads were bought from a salvage yard and the guy said he was gonna have them tested. but i dont think he did. i also replaced all other parts cause the mechanic said that was probably the problem. ign control module. new pcm. ign coil, water pump, timing chain, plugs wires, cap rotor, so should i have the engine tore down again and checked. with all those new parts im really upset cause im a female and i had a feeling he would have taken advantage of me.. cause now i cant get ahold oh him.

 

Sounds like you have no choice if you want you truck running. There are a lot of good mechanics & garages. Find one & take it to them and let a GOOD MECHANIC that stands behind his or her work.