compression test result ..confused

[dyerboy]

So, i have been trying to diagnose the engine loosing power over the last few weeks and finally got a compression test done at mazda dealer.

I fully expected it to fail but dealer assures me it is well within mazda acceptable levels.

From what i have read, i make it a clear fail.

Rotor 1 @308rpm.  
06.5
06.4
06.4

Rotor 2 @303rpm.  
07.5      
07.4      
07.2


Looking at the graph i would say its is well below.

Can someone clarify for me please.

[mikey-t]

8 is the highest you will get, most well used runners score 7, 6 is starting to wear and not too healthy but still running, anything in the 5s or below is looking at rebuild imminently

[dyerboy]

Thankyou for the reply

Are this values at 250rpm or is that bit not important?

[Prof]

There is a graph / equation for recalculating the value for 250 rpm.  Good figures are quoted for 250 rpm, a lower rotation speed during the test will give lower values, so you can \'factor\' them up accordingly.  Your test speed is quite a bit faster than 250, so those results need to be reduced to give the real picture, meaning your front rotor is more likely down in the bottom 6\'s or high 5\'s and that\'s not so good.

[Ashp1989]

I thought u did a comp test with no revs. Take the ignition fuse out. Pip from wgt did mine 2 weeks ago and both front and rear rotor were in the mid 7\'s that\'s on a 40,000 mile engine with no rebuild. I was quite happy

[steve garbutt]

Ash : when you crank the car its making revaluations, 250 rpm during cranking is the baseline.

Dyerboy : As Prof says you have to round down the results to 250rpm during cranking, when you round down your results that come out as, approx

5.44
5.34
5.34

6.52
6.42
6.22

[Prof]

I thought u did a comp test with no revs. Take the ignition fuse out. Pip from wgt did mine 2 weeks ago and both front and rear rotor were in the mid 7\'s that\'s on a 40,000 mile engine with no rebuild. I was quite happy

Compression test is done with the EGI fuse out (don\'t want fuel and spark), and with one set of plugs out (I take out both leading plugs), then you crank the engine on the starter. Because different starters / flywheels will spin the motor at different speeds, there is an adjustment table to normalize the values for 250 rpm. Don\'t forget, compression will be higher with a faster engine, and you have 3 chambers to measure per rotation, so no static test is possible.

[Prof]

This looks quite useful:
 
https://play.google.com/store/apps/details?id=eu.revolutionapps.rx8cc
 
and an apple one here:
 
https://itunes.apple.com/gb/app/id497387863?mt=8
 
For the RX8, but the maths is similar...

[dyerboy]

so as suspected, Mazda dealer cant understand their own figures.

Baaad neeeews.

Thank for the input everyone.

Looks like its rebuild time or conversion to flintstones style.

[Arnie_O]

This is happening more and more it seems.
I see lots of cars dealers have said are toast but their compression results say otherwise