2nd Generation Specific (1986-1992) 1986-1992 Discussion including performance modifications and technical support sections.

How to check for good compression on S4 13B motor on the ground?

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Old Apr 27, 2010 | 03:45 PM
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From: Lafayette LA
How to check for good compression on S4 13B motor on the ground?

So I have a motor out and on the ground that a customer gave me to put in his car, and he says its good... However, I would like some sort of way of checking before I just go put it in. I do NOT have the mazda compression test tool, so I will need another idea other than that.
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Old Apr 27, 2010 | 03:50 PM
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From: KCMO
Bolt up a bellhousing and starter, use a standard piston compression testor, just hold down the air bleed and check for consistent pulses, should be very close on both housings.
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Old Apr 27, 2010 | 07:20 PM
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^ Yep. Prop the throttle plates open and add a small amount of oil into the combustion chambers through the exhaust ports / spark plug holes. If it's bone dry inside, compression numbers will come out low. Just don't add a ton. If you add too much, it will produce artificially high numbers, and hide potential problems.
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Old Apr 27, 2010 | 07:26 PM
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to spin the engine jump the the starter with a car battery, and use piston ccompression guage as said before
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Old Apr 28, 2010 | 01:22 AM
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so does this method work with the electronic testers that mazda used to use? I know there was a nice one that printed everything out, and, I think, one that just showed the numbers on LED
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Old Apr 28, 2010 | 01:28 AM
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Originally Posted by AUGieDogie
so does this method work with the electronic testers that mazda used to use? I know there was a nice one that printed everything out, and, I think, one that just showed the numbers on LED
Yes, the tester will just read the compression numbers as long as the engine is turning....
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Old Apr 28, 2010 | 01:34 AM
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kinda what i thought.
I't to bad those things arn't cheaper. It would be great to know what all the numbers are instead of just watching it go bump. bump, bump
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