sbrmechanic

Finally mustered up the courage to do a compression test in fear of seeing something unpleasant, and that's what i got, 45 on all six rotor faces, but hey at least its even right? Reading up on some of aaroncakes articles i found that the compression should be above 70 at LEAST, i know i could use a rebuild, but my car runs really well, idles great, and starts right up when hot, did i mess up the compression test?because i feel like it shouldn't run as well on 45 psi

Hiko

iTrader: (2)

Was the throttle open or closed? Only thing I could think for the low numbers, but I'm no guru.

Molotovman

iTrader: (49)

Did you test with a warm engine from the trailing plugs with the throttle wide open?

lastphaseofthis

iTrader: (8)

you mean leading.

stevensimon

iTrader: (11)

how strong was the battery?

also you get better results if you remove the valve in the bottom of the tester than if you just hold the button down. if you just held the button down, you are probably 90+psi

Molotovman

iTrader: (49)

No, I meant Trailing.

lastphaseofthis

iTrader: (8)

you get higher readings from the bottom plug hole. that is the leading hole. the hole size for the trailing is tiny, and restricts air.... how much is debatable.. which would be stupid to debate, when you can just test and get that facts.

that being said, i've never seen REAL numbers from a piston guage, i see bounces to up to 90 psi, even on new engines, or leave the valve in without pressing the button and see a maximum pressure up to 120-130. i want a fancy electronic rotary one like twisted's but haven't got my hands on one yet.

Molotovman

iTrader: (49)

Lol, if you're right explain to me why thè TR-01 instructions tell you to use the trailing hole.

lastphaseofthis

iTrader: (8)

honestly the FSM says to the use the trailing as well. so whether or not you would get a different reading is a moot point, as the fsm also provides the number to compare to.

you win.

Ps, i'm still gonna do it on leading. C=<

RotaryEvolution

iTrader: (30)

apples to apples, i use the leading hole.

philiptompkins

iTrader: (4)

I've never held the throttle open before and have gotten well over 110 on a good motor before (using twisted's gauge)
I didn't know the throttle mattered.

RotaryEvolution

iTrader: (30)

it makes a minor difference but rules out improperly adjusted throttle plates as a cause of low compression.

sbrmechanic

engine was warm but i was using the trailing holes with a closed throttle, about 120 was the final reading if i let the engine keep spinning without depressing the release valve, will redo the test with the leading hole and throttle open

RotaryEvolution

iTrader: (30)

considering your peak is nearly 3 times what your pulses were i would say the initial test wasn't done right or there was a restriction on the gauge.

i always remove the schraeder valve from the line and not the "hold open the release button" method as some others imply works. it may work but the readings are always extremely low and give almost no real info. if this is how you did it then your compression may in fact be perfectly fine, maybe even better than average.

considering the engine starts and runs fine i would probably bet the latter to be true.

nycgps

iTrader: (4)

I always use leading hole

I know FD and FC FSM said to use trailing, but Rx-8 service manual said to use either one.

honestly, i think the Leading plug position looks like a better position to measure compression than trailing imo. that's just me.

plus I use the authentic mazda re compression tester for the test. I'm sure its accurate

sbrmechanic

thanks for the input guys