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Compression on 5.7 EFI

Old 05-15-2007 | 10:20 AM
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Default Compression on 5.7 EFI

What should the cylinder compression be on a 5.7L 350 EFI motor (1999)
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Old 05-15-2007 | 10:53 AM
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dumb question, but I've only done compression checks on 2 stroke motors with kill swtiches, but what is the best way to disconnect the coil to avoid sparking/coil burn out when doing this test?
Please be specific, I'm in learn mode here!
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Old 05-15-2007 | 11:06 AM
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As long as your kill switch is in the off position, you should be fine. I just ran a compression check a couple of weeks ago with no problem.
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Old 05-16-2007 | 09:25 AM
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I don't have a kill switch.
Anyone on the proper compression numbers on this motor?
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Old 05-16-2007 | 09:37 AM
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Just take the coil wire off. The PSI should be around 140-150.
As rule of thumb all cylinders should be with 10% of each other.
You don't want to see 150 in one and 90 in another
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Old 05-16-2007 | 09:42 AM
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By coil wire, I want to clarify. Is this the wire that goes from the coil to the distributer?
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Old 05-16-2007 | 11:57 AM
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On an engine equipped with the Delco EST distributor I usually remove the two harness connectors at the distributor, for T-bolt systems, I just take the wires (purple) wires off the positive side of the coil. Just removing the coil wire is not a good idea.

For a good compression test you should have a fully charged battery and the throttle plate wide open. It's ok to do it on a cold engine. You probably should see about 170-180PSI on an EFI small block. Big block would be more in the 145-165PSI range.

Dave
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