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Compression Testing
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Old 15 Feb 2010, 07:01 PM   #1 (permalink)
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Compression Testing

Level of Difficulty
* * *
A test to see for various reasons especially head gasket failure, basically like a heart monitor you see what way the engine running wise,
1)Make sure your starter and Battery are in good condition
2)Warm the engine up to normal operating temp
3)Disconnect the fuel pump and start engine till it dies
4)Disconnect the ignition system I have the singe coil pack so unclip the connector
5)I started on 1 and 3 cyclinder side so took the airbox out but let the maf sensor still connected
6)Disconnect the fuel injector clips from injectors from all cylinders
7)Take both spark plugs out screw in the compression tester
8)Then put the accelerator pedal to the floor so the trottle be wide open then start engine till engine turns over, time it round 7-8secs starting the engine be plenty, mark the reading
9)Do the both cylinders just like this
10)Next the other 2 and 4 cylinders
11)Take plugs out
Might want to do the 4th cylinder first, take wiper water bottle out, mark down the reading
12)Next take battery out put the compression tester in No.2 cylinder, fit battery again as hard to get at with battery in. So battery connected again same again turn engine over for 8secs while your accelerator pedal to the floor fully down
Once you have all the values they should all be even where mine sitting, their different spec readings for different shape Imprezas but with the readings you got they should be all round same mark if they a very big difference you will have to look further into it as engine has a problem
13)Dont forget fit all plugs bit easier to fit a hose to hold plug and fit it by hand so cross threading the plugs be a lot less chance then
14)Connect the fuel injector connecters
15)Leads back in right order
16)Coilpack fitted and connected
17)Refit everything you took off
18)Connect the fuel pump and job done


Last edited by stiimpreza1984; 10 Apr 2010 at 04:35 PM.
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Old 16 Feb 2010, 08:59 AM   #2 (permalink)
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Re: Compression Testing

Nice. Another good bit of info for me to store in my bookmarks. Got loads of tech info now off you guys
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Old 16 Feb 2010, 11:53 AM   #3 (permalink)
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Re: Compression Testing

Nice even figures across the pots there.
Subaru servicing, repairs and diagnostic fault finding help available.
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Old 19 Apr 2014, 07:11 PM   #4 (permalink)
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Re: Compression Testing

Very useful guide there, well done & thank you!

Well, bearing in mind the motors done nearly 240k, but has been looked after by one owner, here are the results. (Started turbo corner then worked around anti clockwise.., teas nearly do e and haven't time to google locations & firing orders!)

Turbo corner: 149
Power steering revs: 147
Battery corner: 146
Screenwash corner: 143

As previously stated, there were no signs of head gasket failure either from the exhaust, no bubbles in the tank, no sweet smell in exhaust, and no overheating. After the compression test (done dry but after warming up to normal op temp with FOT) im wondering if the usual oil & coolant port has got a slight crack in it? If so, if I bypassed the heater matrix first, could I get away with using some steelfix rather than rip the engine apart as it's only going to be more of a fun plaything/hill climb project?
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