And as it turns out, it's the same in the 1ZZ-FE, 2ZZ-GE, 2ZR-FE, and 2AZ-FE engines.
NOTE: Don't do this on a windy day unless you're sheltered from the wind/dust. Be careful of damaging the aluminum threads while the engine is hot (which is usually the intended time to perform testing).
1ZZ-FE COMPRESSION TEST METHOD:
[*] Disconnect negative battery terminal and push it where it can't flop up and hit the negative post.
[*] Remove the EFI relay in the engine bay fuse box.
[*] Remove decorative plastic cover (if equipped): 10 mm nut and bolt, plus weird plastic clips (x2) at exhaust side of the engine. No idea how to remove them properly, mine have been gone for about 5 years.
[*] Unplug ignition coils: squeeze the release tab and use the flat of a standard screwdriver to gently push the plug free if necessary. Don't push the blade under the lip of the plug, just use the broad, flat side. You can also use the flat to press down on the release clip if your fingers are too soft like mine. Again, DON'T PRY ANYTHING, you don't want to damage the plastic!
[*] Remove the two 10 mm bolts from the ignition wiring bracket and gently lift it so it's not obstructing the ignition coils.
[*] Carefully remove the four 10 mm bolts securing the ignition coils to the valve cover.
[*] Pull the ignition coils out and inspect them.
[*] Clean dirt/dust off of valve cover around spark plug holes.
[*] Blow the spark plug holes out THOROUGHLY with compressed air to prevent debris from entering combustion chamber.
[*] Remove spark plugs (plug socket 5/8 in I think. A deep socket will work as well, but you'll need a magnet or needle nose pliers to pick the plugs up and out). You'll need a fairly long extension, they are deep in there.
[*] Reconnect your battery.
[*] Drive-By-Wire: remove throttle body and intake tube from intake manifold, move TB aside. The TB has four 10 mm bolts/nuts securing it, the nuts will need a deep socket. I don't remember how to remove the stock intake because I haven't had it on for years. You can block the plate open, but it may be easier to disconnect it from the intake manifold and set aside.
[*] Drive-By-Cable: while cranking, fully depress the gas pedal.
[*] Gently thread compression tester gauge into the spark plug sockets. Do not overtighten, as aluminum threads are very soft while hot. Turn the gauge so you can watch it while cranking if you're working alone.
[*] You may need to hook the battery to a charger. Turn the key to the "start" position and watch the gauge. The gauge should rise quickly and evenly; something like 50 psi per "puff." You will crank the engine for four or five "puffs," although some manufacturers want you to wait until the gauge reaches the highest point it's going to. If it takes more than 4-5 puffs, you are probably in trouble.
[*] Repeat this test once more on the same cylinder. You will do this test twice on each cylinder, recording your observations. Record what you SEE, not what you want to see.
[*] To do the "wet" test, squirt a small volume of the proper engine oil into each cylinder; 2 squirts from an oil can, or two table spoons. Wait for a couple of minutes, so that the oil goes around the sides of the pistons. The idea here is that the oil will help seal around the rings. The oil cannot get to the valves to seal them, so you're only testing the rings here. When the rings wear, they don't press to the walls of the cylinder as well because they're less springy.
[*] Repeat the compression test on each oiled cylinder.
Today I ran one on mine (2006 base model with 95,000ish miles) during engine repair and engine performance 2 class:
1 was 155 psi (dry); 195 (wet)
2 was 180; 200
3 was 180; 210
4 was 150; 190
So it looks like I've got poor ring-to-cylinder-wall sealing. I'll probably have to rebuild the bottom end soonish? I don't know how soon, really. I'd like to have a clean work space and good lighting, as well as an engine hoist and all that jazz. I have overhauled the bottom end of an engine (LM7) before, but we didn't remove valves or anything like that, plus its heads are about as different as you can get and still have valves.
We ended up not doing a leak down since the instructor is having to do a live job from A/C repair, as well as a melted and heavily spliced engine harness on a 1998 or so GMC C3500.
On closer inspection, the way I was trying to pull it was correct, but I couldn't pinch the release hard enough with my bare hand to get it free.
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