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Old 01-31-2016, 11:36 PM   #1
Ghia Nut
Scooby Newbie
Member#: 201302
Join Date: Jan 2009
Chapter/Region: South East
Location: Birmingham
2005 WRX Wagon
Aspen White

Default Compression numbers are crazy. Need some help here.

OK so my car is down for some maintenance. Doors replaced etc etc. Car was running fine save for a small valve cover leak and transmission leak which is now fixed. I asked my friends to run a compression test. The original numbers looked great at
1: 149
2: 148
3: 149
4: 148

My friends apparently did that with the fuel injectors firing into the engine.

They decided to run the test again after a day and the numbers came back a lot lot lot worse but no fuel going in.

They did both these tests with throttle body closed.

I was so dumbfounded by that that they tested with a different known good working compression gauge and I just got off the phone with them and they said it reverted to the lower numbers. So I'm at a bit of loss as to what I'm supposed to expect from this. All tests were with a cold engine. On the initial first test one valve apparently stuck a little bit then shot up to 149. I just don't understand how it can be a great reading then all of a sudden it goes to absolute **** once there is no more fuel being injected. Any help or advice would be great.
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Old 02-01-2016, 08:39 AM   #2
Scooby Guru
Member#: 70395
Join Date: Sep 2004
Chapter/Region: MAIC
Location: Da-boonies,Va

The motor should be warm and the throttle plate open with ignition and fuel disabled. Maybe you have a professional do the test. Feel free to Goggle "How to perform a compression test"
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