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Your piston or rings or cylinder wall is shot. Time for another motor.

 

x2 - higher compression reading with the addition of the oil indicates rings or cylinder wall issues.

 

 

I'm not so quick to jump to conclusions. I agree the compression test jumped with oil, but it was relatively equal across all 4 cylinders. To say the rings in all 4 cylinders are shot, invalidates the "dry" compression test readings which showed an issue in #4, and also the CEL which triggered only at #4. My conclusion is that the rings and cylinder walls are worn, but still in working condition. And I further conclude that something up top (i.e., valves) might have an issue in #4, which was shown by the dry compression test.

Bottom line...I'm NOT throwing an engine in it (tons of $$$), before I try other things. Heck, I'd throw 4 new injectors, 4 new coils, 4 new plugs, and pull the head to clean the valves WAY before I decided to scrap the engine. I'm not jumping to that conclusion.

 

You could try soaking the cylinders with something like SeaFoam overnight. If you are lucky it can loosen up coked rings, multiple treatments may be needed for best results.

There are scopes available for less than $20 that attach to your smart phone.

Nobody is saying all 4 are bad. When #4 jumped from 93 to the same range as others is the thing. Not that all 4 are similar when wet. That pretty much rules out bad valves leaving the part that is affected by being wet, the rings.

Of course, it could be operator error. run the compression several times with a battery charger hooked up to get many revs and a good seal in the plug hole.

 

I ran the dry and wet tests on all cylinders several times. So there's no issue there.

Perhaps there is a piston problem that I can't see yet, but I'm going to try everything else before scrapping the engine.

I'd like to ask more about the walnut blast...

1. I'm assuming the valve stays closed while blasting. That said, how does walnut blast cleaning the thin face that mates and seals against the head?
2. What about the exhaust valves? Are there concerns about them needing blasted?
3. Is microscopic walnut media left inside going to hurt the engine?

 

RJ RS SS 350 is the authority on shell blasting but, exhaust valves burn hot enough to keep them clean. Microscopic walnut shells will burn off, probably a decent idea to change the oil after.

Amazon has several borescopes under $20, I have seen them for under $10.

 

A cylinder leakdown test would tell you where the compression loss is.

 

Duh! I completely forgot about this idea! You're right!

 

The wet test already ruled out valves/head gasket/injector seals. Maybe you'll find additional leaks.