Mazda 6 3.0 V6. Cylinders 2 and 4 have no compression and the other four do. What would cause this?
This could be caused by any number of problems. The most common are probably:
- Stuck or burned valves
- Blown head gasket
- Burned piston
- Damaged piston rings and/or cylinder wall
Is there any other history of this vehicle that might give some more clues?
But before you do anything else, please double-check your compression tests. I find it odd that there are two cylinders with ZERO compression.