well i just did a comp test and got 50psi per rotor, im pretty sure thats a fail, or is there anything that could cause a false reading, im pretty sure my intake mani is leaking but im waiting on the new gaskets to come in

 

If the starter turns slowly (battery is weak) you could get a lower reading than normal. Is this an original engine?

Did you record the reading for each face of both rotors? What's the difference between each face?

 

the car had just shut off, battery was good, i held in the pressure release on the guage cause my roomie wouldnt let me take the shrader valve out, and both rotors bounced to 50psi max, with litte variation on the two, and im not sure if the engine has ever been rebuilt or not

 

hm... seems like compression is NOT the problem.

 

What do you mean "Bounced" to 50 PSI?

Try doing the test without holding down the valve and see what the highest reading is on both.

 

holding the pressure release on the gauge is not the proper way to do a compression test. your readings are inaccurate. take the schrader valve out or go rent a pressure tester and take it out and redo the test properly.

 

yea i thought something was up with the reading cause there should be some sort of fluctuation if the psi is that low. and when i say bounced i mean every time a rotor face would make compression it would move the needle up until the face was no longer making compression and it was released out of the gauge.

 

well what you are doing by holding down the release is allowing some air to bypass before getting to the gauge at all, skewing your readings lower than they actually are.

by removing the schrader valve in the hose to the gauge it allows the pressure to go to the gauge and peak the needle and dump the air back into the housing once past peak. this will give you an accurate pressure test reading for each rotor face.

 

how many miles mine that has 180k compression is low, other s4 110k has good compression, in denial still on the 180k car

 

odo says 193k

 

Before you do anything drastic, like rebuilding the engine, spend a few bucks and have a proper compression test done with a tester designed for rotary engines. You must normalize any numbers you get by using the charts in the factory service manual. In order to do that, you need a tester that will provide the engine rpm at the time of the test. Even though you think the "...battery was good.", it may be old and weak and not fully charged resulting in an engine rpm significantly less than the 250 rpm used by Mazda to specify acceptible compression.

 

the battery is good, it was installed at the beginning of summer and was just tested at my college (im a auto student) after work tonight i am def going to dig deep into it and see what i can come up with, now im not getting spark from either coil like the cas went bad

 

did u do this test with wide open throttle?

 

Holding down the valve will show you if you have a busted apex seal, because you'll get one bounce and 2 very little bounces.

If you want accurate compression readings for each chamber, you'll need something fancier as others have suggested.