Cylinder Compression test question - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 03-28-2006, 11:23 PM   #1
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Default Cylinder Compression test question

4 Block the throttle wide open (how do i do this ?)
5 Disable the fuel and ignition systems by removing the ECM fuse and the IGN or C31 fuse. (i know how to do this just pull the fuse'* i got that) As an added precaution, detach the electrical connector from the coil pack. ( how do i do that ?)

These are the exact words for step 4 and 5 in my haynes repair manual for doing a cylinder compression check. My questions again are how do i block the throttle wide open? and what does it mean to detach the electrical connector from the coil pack? Is that just removing the spark plug wire from each coil in the coil module.
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Old 03-28-2006, 11:35 PM   #2
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Blocking the throttle wide open will prevent fuel delivery (this is a trick to remember if you flood your car). Do it with a stick on the pedal, or tie the throttle full open under the hood.

Disconnecting the ICM connector (main harness) or disconnecting all 6 coils. Either way.

Or you can pull your ECM fuse to prevent fuel delivery. This will NOT prevent spark, however. The first few seconds of spark are provided by the ICM before the PCM takes over.
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Old 03-29-2006, 01:31 AM   #3
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When I did the compression test on my old bonneville, I unplugged the ICM so there was no spark at all, I also had the accelerator sticked.
I can tell you, at a 152ish thousand miles, my old L67 had from 152-160 lbs in each cylinder.
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Old 03-29-2006, 01:23 PM   #4
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so with the car off in park apply the gas pedal to the ground and hold it down. Could i just put a brick on the pedal to keep it down
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Old 03-29-2006, 01:33 PM   #5
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I wouldn't. You need to be sitting there to crank the car anyway. Don't leave your fate in the hands of a brick.
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Old 03-29-2006, 01:39 PM   #6
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is the ECM fuse under the hood in the max relay center. And which IGN fuse do i pull on the driver side fuse 5A Ignition (Run), Automatic A/C Control, Base Cluster or fuse 1D Ignition (Run/Crank), Chime, Cluster.
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Old 03-29-2006, 01:40 PM   #7
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So how do i keep the pedal down to keep the throttle open
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Old 03-29-2006, 01:41 PM   #8
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Originally Posted by wf2tm51
So how do i keep the pedal down to keep the throttle open
Please...use your foot. Or find a way to keep it open at the throttle body.
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Old 03-29-2006, 02:03 PM   #9
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so when someone goes to crank it over just push the pedal down.
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Old 03-29-2006, 02:09 PM   #10
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Get yourself a helper. Put them in the car. Meanwhile..pull the ICM connector as mentioned. Take out all the plugs.

Have them hold the pedal to the floor. Then crank a little. check your compression. Move to next cylinder and repeat for all cylinders.

Put it all back together.
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