No compression in 2nd and 3rd cylinder in 1989 GMC s15

[vikasintl]

1989 GMC s15 automatic 4 cylinder ...

I found that there is very low compression in 2nd and 3rd cyl. like about 0 psi or 5 psi but 1st and 4th cyl. have 125 psi

is 125 psi ok or it is sill low?

also, truck was running ...can it run on 2 cylinders? not the best but was still running...never gave me any problem.

and is there any other reason why it shows very low compression in 2nd and 3rd apart from either valves or lower engine problem?

Before I take it apart...I want to make sure nothing else is causing this?

 

[2013Denial]

Low or no compression can be many different things. Bad valves, burnt valve seats, worn or broken piston rings, leaky head gasket, cracked head, burnt pistons, etc. You won't know what it is until you open up the engine to find out.

Some of these problems can cause pretty severe damage to other parts of the motor if continued to be run. The damage may already be done if the compression is that low.

 

[98trck]

I imagine you did compression test dry
put alittle more than a teaspoon of oil thru the spark plug hole and run the test
if the compression came up a lot the rings are bad
when you do the test you are suppose to have the throttle held wide open