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This is my 1st time on this forum...Anyways, I wanted to see if anybody knows what the compression readings should be for my car. Also, I've ran compression checks on a few other vehicles, and sometimes there are special things you have to do to disable the ignition. So, the only thing I need to do is just unplug the coil pack in this car, right? Do i have to disable anything else, like the fuel system? Just wanting to do this right. The car is having serious problems and I think the engine may be shot. Thanks for the help...
 

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Eric's video:


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Unplug the primary connector at the coil pack.
Pressing the gas pedal to the floor while cranking will stop fuel flowing into the cylinders.


By the book:

2007 Pontiac G6 | G6 (VIN Z) Service Manual | Document ID: 417222
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Engine Compression Test
Charge the battery if the battery is not fully charged.
Disable the ignition system.
Disable the fuel injection system.
Remove all spark plugs.
Turn the ignition to the ON position.
Depress the accelerator pedal to position the throttle plate wide open.
Start with the compression gage at zero and crank the engine through 4 compression strokes, 4 puffs.
Measure the compression for each cylinder. Record the readings.
If a cylinder has low compression, inject approximately 15 ml (1 tablespoon) of engine oil into the combustion chamber through the spark plug hole. Measure the compression again and record the reading.
The minimum compression in any 1 cylinder should not be less than 70 percent of the highest cylinder. No cylinder should read less than 690 kPa (100 psi). For example, if the highest pressure in any 1 cylinder is 1 035 kPa (150 psi), the lowest allowable pressure for any other cylinder would be 725 kPa (105 psi). (1 035 x 70% = 725) (150 x 70% = 105).
• Normal -- Compression builds up quickly and evenly to the specified compression for each cylinder.

• Piston Rings Leaking -- Compression is low on the first stroke. Compression builds up with the following strokes, but does not reach normal. Compression improves considerably when you add oil.

• Valves Leaking -- Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you add oil.

• If 2 adjacent cylinders have lower than normal compression, and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the cylinders.
 

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Discussion Starter #3

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Did the compression test. weird readings...

Cylinder#[email protected] 70psi....Cylinder#[email protected] 100psi...Cylinder#[email protected] 120psi

Cylinder#[email protected] 180psi...Cylinder#[email protected] 180psi...Cylinder#[email protected] 180 psi....

I'm thinking head gasket. My brother thinks its a catalytic converter. There is a story behind this engine...Let's just say it wasn't taken care of very well in another's care.
What are your engine symptoms? Any codes?

Did you use a screw-in tester or hold-in-place type? I know bank 1 is tougher to test. Are you confident in those test results?

I assume those are the dry test results. How about doing the wet test now on bank 1?

How many engine miles? Since the bank 2 numbers are so high I have to suspect a technique issue. It's not meant as an insult.

A compression test just tells you the max pressure the cylinder can hold with the valves closed. The clogged cat wouldn't affect it.
 
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