Home compression test results
 

Hey everyone, my warranty expires Saturday. So I decided to do a home compression test. I don't suffer from any of the classic signs, but I just wanted an idea of what shape my engine is in.

My results:
R1: 100, 100, 100 (105 with valve installed) rpms 330
R2: 100, 100, 100 (110) rpms 332

Acording to the chart I'm below minimum compression for my rpms. Should I call in and try for a new engine? I don't think I will qualify since I have no starting/running issues. I average high 15mpg(mostly stop n go) and can get 22mpg if I'm driving all highway.

Your thoughts?

-Shawn

Sorry posting from my phone, here is the chart I'm using....
https://www.rx8club.com/attachment.p...6&d=1266716801

I recently took my car to the dealership to get a compression test (I was not having any starting issues either) before the warranty expires and it failed the test. Now I am waiting to get a new engine so it might be a good idea for you to give it a try (they are probably going to tell you that they need to do the test though).

do you have a rotary comp tester? if not what did you use. if you do have one would you consider renting it to me?

^ You can use a normal compression tester but you have to remove the check valve in it and then there is a certain way to do it.

1.3,

I would take it in and tell them you have noticed your mileage dropping and a loss of power. Another way to see if your low on power is to do a 3rd gear highway pull (not race) from 50MPH-80MPH against another stock 8. On my last two engines (don't laugh) the loss of power was very gradual and most owners would not recognize it as a problem. On my last motor I did notice a lull in the power band but not really a loss of power. We do regular cruises here and on a few occasions I would have trouble keeping up with the other somewhat stock 8's pulling onto the highway, etc. so I knew something was up.

could you please enlighten me on how to test my motor with a normal comp tester, or is there a thread on this subject

This is not RX-8 specific but gives you a general idea.

http://www.rx7.org/Robinette/compression.htm

I used a standard compression tester. I have a obdll reader that does live data feed (how I got the rpms)

I have gone against my buddies 05 6spd many times now. He has a few mods: lighted flywheel, rp mid pipe (gutted), Ms cat back, bhr ignition, and short shifter. I stayed on his side everytime (I was stock at the time) he has about 40k on the original engine.

As far as mpg, it has only increased since I got the car.

The car starts in under 2secs regardless of engine temp, or how long it's been since I shut it down.

I do have every single receipt for everything I did myself (oil/coolant/oem ignition system/engine mounts/ect) and it's all logged on mymazda.com.

The main problems are: I use 10w-40, no start/run issues, it's a 120mile trip to go, getting off work to go, I'm catless. Im being promoted again and start a new location tomorrow, with a new scheduel. So I feel like the odds are against me....

One other thing... I used the trailing holes for the test. I did search but found only one post that mentioned which to use (leading or trailing) so I hope I got that part right...

Call the dealer, tell them you are going to drop the car off the night before the service date.

Get a friend to drive with you.
Drive to dealer, leave car in parking lot, and drop keys into service slot with envelope written up with your contact information, and the service desired (compression test).
Leave oil change and service history on passenger seat, and leave a note in the key drop envelope that the service history is on the passenger seat.
Have friend drive you back home.

Call dealer up on day of service and see if they ran the test.
If they say yes, all's good.
If no, ask if they will get it done today or the next.

Once they have the test done, then you will know where you stand.

BC.

Unfortunately, The above never took place.... Work never let me off, and I wasn't able to find someone willing to bring me drop it off and bring me to work while its in the shop. Today is the last day, guess I'm gonna ride this engine to the ground. If it last about a year (10k-12k miles) I will be able to save up for another better built one. As long as its not giving me issues, I'm not really to concerned at the moment. I'll just continue to monitor it.

need to do this on my engine as well, which fuse will disable ignition?

You can unplug the ESS, or unplug the coils. If you unplug the EES you will not be able to get a rpm reading when testing. I was unable to find a fuse that disables the ignition and still allow the car to crank.

Isn't there a fuel pump fuse you can pull, that would do exactly that?

BC.

Honestly, I rather disable the ignition than the fuel. I've been shocked by a GM 3.4L v6 ignition coil.... It will never happen again, that shit hurts!

ok so I did the test tonight. I used regular compression test gauge from AZ

when holding the pressure release valve open needle would evenly bounce each time to:
R1(front): 60, 60, 60psi
R2(rear): 60, 60, 60psi

these seem awfully low!?

pressures with release valve closed needle would hang around:
R1(front): 100, 100, 100psi
R2(rear): 90, 90, 90psi :-(

don't know what my rpms were but looking at the compression chart 100+psi should be good ballpark for a wide range of rpms?

what do you guys think?

Can't say much without a rpm reading, do you know anyone with a obdll that does live data feed?

All you have to do is plug in the scanner and crank with the gas pedal fully depressed to get your average cranking rpm. Shouldn't make to much of a difference between the plugs being in, my cranking rpms are nearly the same with The plugs in or out.

But those numbers look a little scary :uhh:

when you got your 100psi reading was that with pressure release valve open, in another words did the gauge needle sweep 0 to 100 psi for each rotor face?

even without knowing my cranking rpms difference between R1 and R2 pressures is what worries me.

I used this as a guide for my testing:

Compression test using a piston engine tester:

1. note battery strength. A weak battery will yield low compression results.

2. Remove R1 and R2 upper plugs.

3. remove fuel pump fuse.

4. have a friend floor the accelerator pedal, opening the throttle for more airflow

5. insert your tester into the leading hole

6. hold the valve on the side of the tester open

7. have your friend crank the car over for 5+ seconds.

8. observe the needle bounces. You should see 3 in succession without skips, even bounces, in roughly the 30-35psi range.

9. let out on the valve now, and let the tester reach an overall compression value for all 3 faces(highest of 3 will be displayed). 115+ is like new, 100-115 is healthy, 90-100 is getting weak(1 year or less in most cases) below 90 could blow at any moment.

10. repeat for opposite rotor. Note difference in overall compression between rotors, which should be no more than 20psi max.

Yep, i got 3 0-100 sweeps.

That is pretty much how I did mine. Except I had disconnected my coils (for my own safety).

If there is a harbor freight near you, they sell a rpm reader that you point at the crank pulley to get a reading, just seen it, never tried it.

Maybe your tester had a leak? I would test again to be sure. If you get the same numbers it's time to start gathering everything you need and go to a dealership. Be prepared to spend about -$200 for the test. I would call first to set up an appointment.

I doubt I had leak since it would hold 100psi on R1 and 90 psi on R2 without release valve open and when we stopped cranking. Bummer..

Well then, I think it would be worth going to Mazda for an official test. Sorry :(

Here I am, a year and a half later and about 13k miles. Did another home compression test today. Used the same gauge and same method.

Results...

R1: 95, 95, 95, (100 valve on) RPM 278
R2: 97, 97, 97, (102 Valve on) RPM 284

Still got some life left in my dirty old rotary. :D:


And I got to touch a apex seal again. ;)

need to do mine again..as long as she starts quickly when hot I think we are fine.

Funny thing is, when I use the compression app to normalize the rpms to 250 it shows I've actually gained compression.