How To Check Your Engine's Compression

[Keeper]

so, where's the cas?

front of the engine, left side of car, round thing at the front of the exhaust cam

[Keeper]

im going to give the electronic method a go tonight,

disable idle adjustment from engine and check the drop in rpm in each cylinder, measure it and see what makes the least difference.

in theory this should tell me if i have 1 cylinder that is crap right?

didnt work

[turbo_brian]

Nobody has mentioned the wet/dry arguement yet, so here I go with the spanner in the works.

When I do a compression test (usually I only bother on cars I am buying), I do 2 tests, a dry, followed by a wet test.

I do as mentioned in Manual method, remove the ignitor, spark plugs, set WOT, also remote the fuel pump fuse, and test cylinder by cylinder with my readings written down.

Then I get a bout 10ml (cap ful) of CLEAN engine oil into the cylinder hole and leave it for a minute or 2 so that the oil can spread to the edges of the piston and form a thin layer and SEAL the piston ring area.

Then I re-test as above, and re-record the results and figures.

The reason for doing this is because in Dry testing, you get figures based on what the piston is pushing up, minus any pressure lost through the rings, and any pressure through the valves.

In Wet testing, you get the piston pressure minus any pressure lost through the valves, so it gives you a little bit extra in information.

If you see MASSIVE difference in figures from a wet and dry test, it means the rings are worn, and you would have gotten low-ish readings from the initial test.

If you see almost no difference, it shows the rings are in very good condition, not loosing much pressure at all, but if you still have low readings, you might need to check your valves and seats.

I last did a compression test on a Toyora Soarer 1JZ.

Dry:

1: 165 2: 163 3: 167 4: 165 5: 164 6: 168

Wet:

1: 169 2: 168 3: 172 4: 168 5: 167 6: 172

This test shows that in both figures the engine is healthy, there isn't a huge difference in figures from piston to piston, and the figures are high enough to show there isn't much pressure loss or wear and tear.

The wet figures are all around 3 - 5PSI higher than the dry figures, so there is a small amount of pressure lost on the rings, but not a great deal, nothing to be concerned about.

It also shows that the vavles are sealing nicely, and are not an issue, I was happy with these figures, and purchased the car

B.

[errno]

hey guys sorry to bump a real old thread

just wanna make sure im gonna do this right

firstly is this compression gauge going to be suitable: http://imgur.com/bzHN3.jpg

secondly, would i be right in thinking a good way to crank the engine to get a reading would be

- disconnect CAS + coilpack loom

- depress accelerator fully for WOT

- turn key as if i was starting the car

- go check reading on gauge, do this for dry and wet test as poster above.