Compression testing

[Dras]

I am looking at the workshop manual at the section regarding compression pressure check. It all looks pretty straight forward but I do have one question.

Keeping in mind that for this test you need to remove all of the spark plugs and disconnect the crank angle sensor, the manual states 'crank the engine with the throttle valve fully open'.

(I can just picture me holding the removed throttle body in my lap in the cabin, holding it open with one hand and turning the key with the other and looking puzzled. If I was better at drawing I would include a picture.)

This has me a little confused. Do I need to re install the intake manifold after removing the spark plugs? Is this just so the air entering the engine is filtered? If so, what about the spark plug holes?

If disconnect the crank angle sensor stops the ECU from carrying out ignition and fuel injection, the only thing I am achieving by cranking the engine is turning the starter motor. I just can not see any good reason for the intake manifold having to be reinstalled or opening the throttle valve if the intake manifold is not installed.

[Bennoz]

lol, stupid asian manual.

You do 1 cylinder at a time. Disconneting the crank angle sensor prevents the engine from starting - as even with only 5 plugs connected it will still fire & run rough.

Also pulling the intake off is the same as having the throttle wide open.

All you want to do is have the starter rotate the motor whilst you do each cylinder, whilst it is just breathing air, replacing the plug of the previous cylinder as you go.

[Dras]

Really, most things I have read seem to suggest that all the spark plugs should be removed.

[Bennoz]

My bad, you are quite right.

[I8A4RE]

Absolutly.... remove all plugs and intake manifold. Its best if you have a friend help but it still can be done by yourself.

If your doing a compression test, I highly recommend you do a leakdown test as well. Depending on what your testing for, it is much more informative when diagnosing.