I have a 2005 Trailblazer with 4.2L, 85,000 miles.

I took a compression reading and came up with the following:
1: 40psi
2. 120 psi
3. 125 psi
4. 122 psi
5. 120 psi
6. 124 psi

The #1 cylinder is obviously the problem. The spark plug had a bit of oil on it.

Is the consensus that the problem is in the head / valve train? Or the piston / rings? Would it have anything to do with the variable timing solenoid?
I am wondering if doing a head job will fix this issue, or if I need to go full engine.

Also, I don't have a cylinder leak down tester.

Thanks in advance.
J
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There is only 2 ways to determine top end or bottom end issue. The easiest is a leak down test. Since you do not have one then you need to remove the head for inspection to see if you can see the problem.