What do my compression test numbers mean?

As the other person said, your 4th cylinder is trashed. A compression test measures the amount of air pressure your cylinders along with your air/fuel mixture and helps your mechanic determine if, and where you may have engine problems.

Simply put:

Air and gas go into the engine cylinders. Your piston then pushes down into the cylinder where it creates compression (pressure). Then your spark plug ignites, causing a small explosion that forces your piston back upwards and in turn powers a crank which eventually feeds down through your transmission and provides power.

Since the cylinder is sealed, the used gasses from the explosion are removed by your exhaust valves, which feeds into your exhaust.

The amount of air/fuel mixture in the cylinder coupled with the pressure from the piston pushing down creates what is called a "compression ratio". If your cylinder isn't able to produce the correct ratio, (due to the incorrect amount of fuel or air)you lose power. I would venture you have a pretty severe leak somewhere in that cylinder which is why you have 0 compression.

I would assume your mechanic did a leak down test as well? This test focus's solely on the cylinder (excludes air/fuel ratios), and should be able to tell you where in your cylinder/engine there's a leak.

I would be saying that you have a set of head gaskets blown besides other things.For one it seems you might need a valve job and or a valve job and piston rings replaced.But in the long run not knowing how many miles you have on the car I would be saying your better off getting a rebuilt engine and putting in or have this engine rebuilt.You have a 25 pound difference between the highest reading and lowest reading that tell me that its time for a rebuilt engine because you didn"t say how how many miles you havre on this engine.But my strong point is replace the engine other than having the top end rebuilt along with the piston rings.You have a blown head gasket because of the readings I am looking at on one of the cylinders that has 0 reading.Your compression test tells you how many pounds of pressure you have in the cylinder or cylinders for up to how many cylinders a person has in a engine weather being 4,6 or 8 cylinders.You woyuld be better offf getting a new engine but beware there might be a core charge on the old engine for the new engine.hgm20002000@yahoo.com

cylinder 4 is shot(bad rings, bend valves, hole in top of piston...) Cylinder 8 is about right. The others are a bit low but at least they are in an acceptable range of each other. You are only running on 7 cylinders. May be time for a rebuild.

burnt or bent valve, hole in piston ,melted piston,no compression rings left

did you do a wet test on that cylinder to see if it changed