New compression readings

EUGENE PARKS JR

MEMBER
2006 CADILLAC DEVILLE DTS
V8
2WD
AUTOMATIC
81,000 MILES

After explaining my vehicle had lost compression to cylinder #6 and mechanic was talking about tearing down the engine or even replacing it, you requested the compression readings yourself.
I personally checked all eight cylinders. All were
175 dry and 180 wet. But the #6 cylinder was 0 dry 0 wet. I removed the valve cover and it all looks like new due to always maintained. Nothing look out of normal.
Now, where do I go from here?

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

Hi Eugene,

That is great. If you have no compression on this cylinder then it has clearly failed. I attached a guide of the reasons for low compression.

I would do two things from here. First, run a cylinder leakage test. This will tell you if it is a valve and which one, or if it is a head gasket, or piston rings.

The way to do this is to put air pressure in the engine with it on TDC on the compression stroke. This way, the cylinder is supposed to be sealed to build compression and if you apply air pressure you will have air escaping the source of your issue. Either the intake (intake valve), exhaust (exhaust valve), valve cover or oil fill location (piston rings), or lastly the coolant reservoir (head gasket). I would not put full air pressure to the chamber because you could close a valve if it is too high. All you need is about 15-20 PSI. If you don't hear air anywhere, then increase it 5 -10 PSI until you hear air escaping one of these places.

Second thing is to put a borescope down the spark plug hole to see if you can see any damage. If it is not making noise when it is running then you may not see anything.

Depending on where you hear air coming out, it will dictate what your next step is in repairing the vehicle.

Let me know what you find and we can go from there. Thanks

https://www.2carpros.com/articles/the-reasons-for-low-compression