420A 2GNT chasing a smoking issue

[zheter]

I did a compression test on my 8.8:1 low-compression 420A and got these results:

• Cylinder 1: 165 psi
• Cylinder 2: 180 psi
• Cylinder 3: 165 psi
• Cylinder 4: 180 psi

One thing I noticed is that after I stop cranking the engine, the compression gauge pressure slowly bleeds off.
I'm also chasing a smoking issue. After the car has been sitting, it smokes on startup, but once I start driving, the smoke goes away. After a couple of miles, it doesn't smoke at all.

I'm wondering what the most likely cause is. Could this point to worn piston rings, valve stem seals, or possibly the turbo oil seals? The compression numbers seem decent to me, so I'm not sure which direction to investigate first. Any advice would be appreciated.

 

[BLACK'98DSM]

The compression numbers are good. Not like fresh rebuild good, but far above service limits. The variation isn't preferable but it is consistent if you pair up the cylinders and shouldn't cause a misfire or other noticeable issues.

What you will need to do is some diagnosis. Normally a cold start smoking issue that clears up points to valve seals. There could however be an issue with oil rings only, in early stages.

What I would recommend is removing the exhaust manifold from the head and see if the exhaust valve stems are wet with oil. It's slightly labor intensive on a turbo build but will definitely tell you next steps or perhaps the culprit.