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

low compression! help

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Old Mar 20, 2011 | 02:00 AM
  #1  
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CA low compression! help

so today i decided to do a compression test to see where my motor stands.
seeing if i did this correctly (removed both top plugs and stuck the tester in one rotor at a time.)
and when i cranked the engine i was getting 70-80 on each pulse.
i was reading that the readings can be inaccurate if your plugs are carbon fouled.

does this make any difference? or does it mean my cars gonna blow any second?

is there any way i can fix this without rebuilding my engine.

i dont understand why the compression is coming up so low, because the car drives fine (other than the flooding).

and even if i were to get it rebuilt karack is too far (vegas) and i dont think i can make it.

any help would be great.
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Old Mar 20, 2011 | 07:22 AM
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If you really doubt the numbers, take it to a Mazda dealership and pay for them to do a compression test. Their tester is going to be more accurate.
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Old Mar 20, 2011 | 10:05 AM
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70-80 pulses is really low.
My S4 does 80psi on all faces and its really struggling compared to 3 years ago when it had 90psi on all faces. I have 155k miles on the engine, but its been beaten to death lol

I would say get it rebuild.
Either get new housings or get the housing refinished so when you install new apex seals, the compression should be 110+
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Old Mar 20, 2011 | 10:14 AM
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If the car drives fine, it could continue to run like this for years. There's no reason to immediately worry.
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Old Mar 20, 2011 | 09:30 PM
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Install a fuel cut switch and go on about your business.

http://www.rotaryresurrection.com/2n...ooding.html#a5
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Old Mar 20, 2011 | 09:49 PM
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Originally Posted by jackhild59
Install a fuel cut switch and go on about your business.

http://www.rotaryresurrection.com/2n...ooding.html#a5
i do have a fuel switch wired directly to my fuel pump.

oh and another question can a vacuum leak affect your compression readings? i think i have a turbo or an exhaust leak also im not sure. but yeah can they affect compression a whole lot?
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Old Mar 20, 2011 | 10:24 PM
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Nope.
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Old Mar 20, 2011 | 11:06 PM
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technically a huge vacuum leak, like having the intake ports open to the atmosphere (no runners or anything) could potentially give you higher readings, but it could be negligible compared with the increase you'll see from properly warming up the motor first and holding the throttle open while you crank. but a regular vacuum leak? see above.
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