DeCoY

Longer version:
I decided to check my compression on my JDM B18C today as a sort of "wellness check". I observed 120-140psi on cyl 1, 2 and 4 (I know these are low numbers but I live at high altitude so I think that can affect it some).
On cylinder 3, there is 0 COMPRESSION, the needle doesn't even move. I tested and re tested to make sure I wasn't doing something wrong, all the while getting responsive readings on other cylinders. Other than some minor idle/throttle issues every now and then, then engine pulls strong and I recently averaged 37 MPG on a road trip. Another observation is that with the engine running, if I unplug the offending spark plug, there is a noticeable difference in the sound of the idle. I thought if it really was at ZERO compression, it wouldn't make a difference to un-plug the spark wire.

Short Version:
Zero compression on one cylinder.
Car runs strong and does not sputter/backfire/smoke.
Removing plug wire from offending cylinder causes idle to drop/become rough.
Tested multiple times, switching from other cylinders showing readings.
No check engine lights or trouble codes.

Is it possible to have a cylinder at ZERO compression and only have minor symptoms???



Thanks for reading!

DeCoY

Follow up:
I decided to try a little experiment. I removed the plug wire from the offending cylinder, connected it to a grounded spark plug outside of the engine (as to not damage the coil) and I took it for a drive up the street. Not only did the car sound like a WRX but it was running like *** with a noticeable power loss and strong engine vibration.

I am convinced my zero compression reading on that cyl was somehow in error even though I tested it multiple times. I am going to buy a new compression tester and try again later.

Thanks for reading.

tallguy

Did you do a dry or wet test? Its hard to believe you have zero compression with no side effects.. like loss of power or excessive smoke. You could try a leak down test to see if you have air coming out of the throttle body,exhaust, or oil fill location.

DeCoY

I decided to purchase a new compression tester and retest.
The offending cylinder is now showing 70 psi dry, and 90 psi with some oil squirted in.
All other cylinders are showing 150 psi dry.

It would seem apparent that I have a "weak" cylinder. The car still drives well and seems to have enough power, but I am still very saddened knowing my engine is not at 100%

What would you do if it was your baby?

AYB18c

This is a tough situation because you say the car's running fine. So unless you're burning oil, it appears you don't have much in the way of symptoms....so why fix what you're not noticing is broken? At some point it's gonna be noticeable though, either losing oil or misfiring or something...but whether that happens in 10k miles or 100k miles is anyone's guess. Being that you're on H-T though you want your b18c to be the best it can be, so.....

If it's your "baby", rebuild it. Causes of low compression include (but aren't limited to) worn piston rings, leaking intake/exhaust valves, worn valve seals....other things come to mind like head gasket but I would think that would not just be localized to one cylinder.

If you're willing to do the work/spend the ime/money, pull the head & check the valves, replace the piston rings in that cylinder, check the piston/rod while you're at it for any craziness. put it all back together. profit.

DeCoY

I am willing to take the head off, but I need to be sure it is the head first. If there is damage to the rings/pistons/sleeves, it is probably not worth the time and money.

I will try and do a leakdown test in the near future to try and pinpoint the failure.

And yes, this car is my baby. I bought her in 2004 and I still love her just the same today as the day I first saw her lol. It's easy to see why: https://s4.postimg.org/ynmior75p/Civy.jpg