Cody Red

So I went by the nearest Mazda yesterday to do an 'under the table' compression test (under fear that the numbers may be low, and not wanting Mazda to see).

we only had time to do the test to the front rotor, using the RE compression tester.

Rotor 1:

250 rpm:

Chamber 1 - 7.9
Chamber 2 - 7.9
Chamber 3 - 8.0

I know these figures are pretty good (right?) because when I searched for another compression thread, i read that 6.5-8.0 is good. Is this correct?

Now, what are the chances that rotor 2 will be bad? I ask because at some points when driving the car, i feel some power loss when pulling in second and third. As well as low rpm's at stops. Sometimes experiencing 500rpms and up to 700rpm (varying) with the a/c off. Also when gear changing at WOT (2nd, 3rd) it'll misfire and then start to accelerate.

I don't know if it helps, but after long drives my exhaust note begins to get deeper, and sometimes sounds more irregular than deep. 9/10 times the exhaust pops when changing gears (idk if that helps).

It's an '04, with 24,3xx miles, original motor, my last oil change was to 5w20 in which it needs an oil change soon. I've had a high flow cat on since about 15k miles, and I have a feeling it's going out. But with the more on-going problems I am having with the car (transmission is fuct (dealer won't warranty, a/c not always blowing hot when the weather is cold, this on going **** with powerloss and low rpm stuff) i am starting to feel the need to trade it in before anything worse happens.

Any thoughts, suggestions?

Thanks for reading.

Go48

The "minimum" spec is 6.9 kgf-cm2 at 250 engine cranking RPM. "Standard" is 8.5 at 250 RPM. Standard difference between "chambers" is 1.5, and standard difference between rotors is 1.0.

So, in order to evaluate the health of your engine, you need to know the engine cranking speed at the time of the test and you need to know the comparable numbers from the other rotor. Higher or lower RPM can make a difference in the numbers presented by the tester. Assuming the engine was cranking at about 250 RPM, your numbers look very good. Your "power loss" may be due to low compression or to something else, but you won't know until you finish the test.

As an aside, do you have an aftermarket oiled air filter element? If so, your MAF sensor may be oil-fouled causing incorrect readings being sent to the PCM and causing the problem.

Cody Red

the intake is a REVi.

Go48

Remove your MAF/IAT sensor (see the Factory Service Manual) and check for oil on and up inside the sensor. If you find oil, very carefully clean it with something like CRC Mass Air Flow Sensor Cleaner. Do a search of the DIY section for information on how to do that.

Edit: Check out this thread: https://www.rx8club.com/showthread.p...&highlight=MAF

Cody Red

btw, is kgf-cm2 the same as kPa?

i'm assuming so.

Go48

Nope. See the attached image.

EDIT: Wikipedia definition:
Kilogram-force per square centimetre

A kilogram-force per square centimeter (kgf/cm2), often just kilogram per square centimeter (kg/cm2), is a unit of pressure using metric units. Its use is now deprecated; it is not a part of the International System of Units (SI), the modern metric system. The unit is similar to the English unit psi (lbf/in2). In SI units, the unit is converted to the SI derived unit pascal (Pa), which is defined as one newton per square meter (N/m2). A newton is equal to a kg·m/s2, and a kilogram-force is 9.80665 newtons, meaning that 1 kgf/cm2 equals 98.0665 kilopascals.In some older publications, kilogram-force per square centimeter is abbreviated ksc instead of kg/cm2.

Aren't you glad you asked:

I8U

iTrader: (1)

If those numbers are considered "standard" then I must the best f'ing motor ever built...I have an '04 with 23k+ on it's second motor and my numbers were:

rotor 1 @ 267rpm
9.7, 9.6, 9.6

rotor 2 @ 263rpm
10.2, 9.7, 9.9

I've only used 5w30 full synthetic, and changed ever 4k miles...also, run 5oz of premix ever other tank. Recently installed HKS HiPower and K&N V2 intake.

Go48

Yeah, even with the higher cranking rpm, those numbers are unusually high. See my graphic. Would you mind providing a bit more info on how the test was conducted? Like for example, what tester was used, where was the test done, was the engine warm, gas pedal to the floor during the test, etc. Thanks!

I8U

iTrader: (1)

Sure, the test was done at my local dealership using whatever tester they normally use, the engine was very warm since I had to drive almost an hour to get there and they took it out for a test drive. It was on the diagnostic machine for about 30 minutes running before they decided to do a comp check. As far as the gas pedal, I'm not sure...I only the have reading that they wrote down on the service ticket.

Also, the previous compression check that was done 4 months ago produced numbers pretty close to ones that came up now.

tdiddy

Those numbers are close to what I saw at the same milage.

Rotor #1 - 9.6, 9.9, 9.7 at 274 RPMS
Rotor #2 - 10.0, 9.8, 9.7 at 270 RPMS

Go48

Many thanks for the info!

claus

BTW, PREMIXING really helps with the compression numbers !!!