04' Sport Trac 4.0L 0psi in cylinder#3

[Shelby302]

Was out driving (Doing bout 60-65) when it started to run a lil rough (aka fighting to keep itself running). Couldn't figure out why, Then I did a compression test & 0psi in #3. So I now assume a valve is stuck open. Someone told me there could be a hole in the cylinder & I do not understand. How could that happen? All other cylinders perform without missing a beat. Before I pull the engine, I was wondering if anybody has any knowledge of this motors common problems related to this or has pointers for me.

 

[koda2000]

Was out driving (Doing bout 60-65) when it started to run a lil rough (aka fighting to keep itself running). Couldn't figure out why, Then I did a compression test & 0psi in #3. So I now assume a valve is stuck open. Someone told me there could be a hole in the cylinder & I do not understand. How could that happen? All other cylinders perform without missing a beat. Before I pull the engine, I was wondering if anybody has any knowledge of this motors common problems related to this or has pointers for me.

I recommend you get a bore-scope and have a look inside cyl #3. That will tell you if you have a valve or piston problem,.

Whichever it is, it's going to be a pretty extensive repair.

 

[icthusrulz]

You can also do a “leakdown” test on it to tell you where the problem is (I say “leakdown” test, but with 0psi compression you can probably just blow compressed air into the spark plug hole with the spark plug removed). You listen for air escaping the cylinder when it’s at Top-Dead-Center (compression stroke) to find the leak.

Hiss from the intake = Intake Valve Leak
Hiss from the exhaust = Exhaust Valve Leak
Hiss from the open oil cap = Piston/Rings Leak

Did your PCM throw a cylinder 3 misfire code?

 

[Tech By Trade]

Bet if you pop the valve cover on that side you will see exactly whats going on.

 

[boominXplorer]

+1 on valve cover. I'd put money on a broken valve spring.