6 psi cylinder two

Tiny
PINEIRO11
  • MEMBER
  • 2009 GMC ACADIA
  • 3.6L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 97,000 MILES
Mechanic says 6 psi in cylinder 2. He recommends a new engine. Is this true?
Friday, January 31st, 2020 AT 7:03 AM

4 Replies

Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

I would ask him to do a wet compression test and then report back with that reading. This will tell you if the loss of compression is due to worn out piston rings or something else, but basically, right now, that cylinder is dead.

Thanks,
Alex
2CarPros
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Friday, January 31st, 2020 AT 11:33 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon,

With only 100,000, it may be worth fixing. A lot of shops do not like to do this repair so they just want you to replace the engine.

Why does it have low compression? Part of the diagram is telling you the failure. Is it valves or is it a piston or rings?

https://www.2carpros.com/articles/the-reasons-for-low-compression

Roy

Engine Compression Test

Tools Required

J 39313 Spark Plug Port Adapter

A compression pressure test of the engine cylinders determines the condition of the rings, the valves and the head gasket.

1. Run the engine until it reaches normal operating temperature. The battery must be at or near full charge.
2. Turn the engine OFF.

Important: Remove the powertrain control module (PCM) and the ignition fuse from the instrument panel (I/P) fuse block.

3. Disable the ignition.
4. Disable the fuel systems.
5. Remove the spark plugs from all cylinders.
6. Remove the air duct from the throttle body.
7. Block the throttle plate in open position.
8. Measure the engine compression, using the following procedure:

1. Thread the J 39313 into the spark plug hole.
2. Thread the compression gage into the J 39313 .
3. Have an assistant crank the engine through, at least 4 compression strokes, in the testing cylinder.
4. Check and record the readings on the gage at each stroke.
5. Remove the compression gage from the J 39313 .
6. Remove the J 39313 from the spark plug hole.
7. Repeat the compression test for each cylinder.

9. Record the compression readings from all of the cylinders.

The lowest reading should not be less than 70 percent of the highest reading.
No cylinder reading should be less than 965 kPa (140 psi).

10. The following are examples of measurement problems:

When the compression measurement is normal, the compression builds up quickly and evenly to specified compression on each cylinder.
When low compression is caused by the piston rings, compression is low on the first stroke and tends to build up on the following strokes, but does not reach normal. Compression improves considerably with the addition of oil. Use approximately 3 squirts of oil from a plunger-type oiler.
When low compression is caused by the valves, the measurement is low on the first stroke and does not build up even with the addition of oil.
Leaking head gaskets will provide the same results as worn valves but engine coolant may be identified in the crankcase. In addition, a leaking head gasket will give low readings on paired cylinders.

11. Remove the block from the throttle plate.
12. Install the air duct to the throttle body.
13. Install the spark plugs.
14. Install the powertrain control module (PCM).
15. Install the ignition fuses to the I/P fuse block.
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Friday, January 31st, 2020 AT 11:41 AM
Tiny
PINEIRO11
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Thank you for your time! I'll give my husband this information and keep you posted.
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Friday, January 31st, 2020 AT 12:07 PM
Tiny
ASEMASTER6371
  • MECHANIC
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You are welcome.

Always glad to help.

Roy
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Friday, January 31st, 2020 AT 12:10 PM

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