X2 in the Seafoam, it could just be a ring gummed or carboned up, at lease #3 increased in compression, ruling out a burnt exhaust valve!

 

Thank you so much, donbrew. I will retest it tonight. What Seafoam shall I use for the top clean? I found two: Seaform Spray and Seaform motor treatment.

 

Thank you very much, Oldblue. I bought both Seafoam Spray and Seafoam motor treatment just now. But would like to wait for your or donbrew's recommendation on which one to be used. Both says cleaning up carbons deposits.

 

I retested following the donbrew's post but it still showed the same result: #1, 2, 4 - 210 psi #3, 90psi (jumps up to 150psi after adding engine oil). To avoid my personal fault, my friend checked each steps I did. We retested #1,2,4 twice, each time got 210 psi with two gauges (one was loaned from Autozone, the other was owned by myself).

Ignore the gauge absolute measurement, #1,2,4 have the same pressure values while #3 has much lower one.

 

Pour a couple of oz into each cylinder let sit at least over night. Maybe do it again.

Worked for me when I had a frozen oil control ring.

 

I figured out they were pretty much the same. So I just poured the motor treatment into the well. I will update the result tomorrow. Now I am crossing my fingers.

 

Thank you, donbrew. Did it already. I will get back here tomorrow.

 

One more question, shall I change my oil tomorrow?

 

I would, or pour the rest of the bottle into you oil, run it for a day or two the change your oil and filter.

 

Update:

I saw all the seafoam was soaked this morning. Then I put everything back and started the car, saw little bit smoke (not too much). After idling a little while (5-7 minutes), the engine code P0303 came back again. I cleaned up the code and started driving. During the driving, when the speed was low, the code came back again. I will drive one day and do the oil change tomorrow.