3rd Generation Specific (1993-2002) 1993-2002 Discussion including performance modifications and Technical Support Sections.

Is OMP Working?

Old 09-01-18, 04:41 PM
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Is OMP Working?

A little nervous here... recently replaced engine, new OMP lines. Nearly 2K miles on new crate engine (almost 115K miles on car). Dipstick indication has not moved since the engine install; still at full. I jumped the "Ten" to "GND" ports in the Diagnostic connector and turned the ignition switch to the RUN position, and the engine check light went on for 1-2 seconds and then went off and stayed off, indicating no stored error codes. That's all well and good; I should have seen a code 20 If the OMP electrical stuff were bad, but why is the engine not using ANY oil? The original engine used about 1 quart between 3K mile oil changes. I pre-mixed with TC-W3 oil for all fuel fill-ups since new for break-in, but wife (owner) wants to quit that beginning at next fueling.

Is the new engine just that good? Or is the OMP somehow not doing its job?
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Old 09-01-18, 05:57 PM
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Lots of possibilities.

-What ECU are you running? I don't believe any non stock ecu will throw check engine light codes?

Now the complicated part because you mention a new crate engine. Mazda changed the OMP system in 99 and I believe new housings are coming with the newer style non slotted jets. See picture here: https://www.rx7club.com/3rd-generati.../#post11943897

The new style jets are accompanied by a rubber o-ring, different injectors with a smaller opening orifice, and a higher flowing OMP.. These all should match for the system to work 100%.

Old style
-Slotted brass jet
-no-ring seal
-Large orifice injectors (no longer available from Mazda and used ones may be non functioning)
-Lower flowing OMP

New Style
-Non slotted
-o-ring sealed
-Smaller orifice injectors
-Higher flowing OMP

As you can see it would be easy for parts to be mixed up between the systems. This could result in a system flowing lower or greater amount of oil. There is also the OMP settings in an aftermarket ECU that could skew oil delivery as well.
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Old 09-01-18, 06:15 PM
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Originally Posted by Brekyrself View Post
Now the complicated part because you mention a new crate engine. Mazda changed the OMP system in 99 and I believe new housings are coming with the newer style non slotted jets. See picture here: https://www.rx7club.com/3rd-generati.../#post11943897
every rotor housing made since 1999 has been the newer style.
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Old 09-01-18, 07:32 PM
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-What ECU are you running? I don't believe any non stock ecu will throw check engine light codes?
OEM ECU.
The new style jets are accompanied by a rubber o-ring, different injectors with a smaller opening orifice, and a higher flowing OMP.. These all should match for the system to work 100%. ... As you can see it would be easy for parts to be mixed up between the systems. This could result in a system flowing lower or greater amount of oil.
every rotor housing made since 1999 has been the newer style.
Arrgh. As far as I know Yoshiya at Neptune Speed bolted the original oil metering pump to the new rotor housing and installed my new OMP lines. I will check with him. Thanks for the tech input... I had no idea there could be a mismatch. I appreciate your help!

After reading your linked thread, it would seem that the new rotor housing injectors would result in reduced oil input to the housing when receiving oil from an original (1994) OMP. Assuming the oil supply available to the OMP is not changed, the new injectors being 0.8 mm diameter versus the old ones being 2 mm would restrict oil flow out of the OMP considerably. I don't really care much for the reduced oil flow (if I'm right) but our car is a street machine with stock hp, so maybe I can stop pre-mixing with nothing terrible happening other than maybe reduced apex seal life. Does that sound right?

Last edited by wstrohm; 09-01-18 at 08:15 PM.
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Old 09-02-18, 10:01 AM
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Originally Posted by wstrohm View Post
Does that sound right?
no, every engine made after 1999 has the newer oil injection nozzles, and they have been just fine with the old style metering pumps.

if anything its better, Mazda found that with the old setup the engine could suck all the oil out of the metering nozzle and then it would be dry for a while. the new ones are smaller, but oil better

"Apex seal lubrication has become a critical issue. In a race engine, oil supply to the rotor housing by means of injection was precisely monitored and controlled, whereas in the production unit, a larger amount is supplied, just to be on the safe side. Some of the lubricant is fed into the trochoid chamber through a metering nozzle. The previous nozzle's oil passage was 2.0 mm (0.08 in.) in diameter. Negative pressure created in the rotor chamber would cause all the oil within the nozzle to be sucked out.
When the engine accelerated rapidly, oil supply could not keep up with the speed. To prevent oil starvation, the previous system supplied a larger amount of oil to be on the safe side. In the new metering nozzle, the passage diameter has been reduced to 0.08 mm (0.003 in.), halving its volume of 0.0005 L (0.03 cu. in.). A new rubber seal is also inserted to fill a gap within the nozzle body where oil used to be sidetracked. Now, there is still some oil left within the nozzle after each suction, so that the lubrication system responds to the apex seal's requirement."

from '99 FD3S
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Old 09-02-18, 10:34 AM
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Premix. Even if you OMP works. If your wife doesn't want to do it at the gas station, you can do it later.
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Old 09-02-18, 12:55 PM
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Once again, thank you for your comments. I would like to point out an error from the linked thread quoted here:
The previous nozzle's oil passage was 2.0 mm (0.08 in.) in diameter. Negative pressure created in the rotor chamber would cause all the oil within the nozzle to be sucked out.
When the engine accelerated rapidly, oil supply could not keep up with the speed. To prevent oil starvation, the previous system supplied a larger amount of oil to be on the safe side. In the new metering nozzle, the passage diameter has been reduced to 0.08 mm (0.003 in.), halving its volume of 0.0005 L (0.03 cu. in.).
According to Mazda's illustration in post #50 (attached), the reduction in nozzle diameter was not from 2 mm to 0.08 mm as quoted, but from 2 mm to 0.8 mm (0.0315 in). Since volume in a cylinder of fixed length is a function of the square of its diameter, the volume in the nozzle was reduced to (.8/2)^2 = 0.16 or 16% of its original volume, not 1/2. (A reduction to 0.08mm would have been essentially blocking all oil!)

In any case I am inclined to accept TomU's advice to continue premixing... just because.

[Edit: I just noted that the reduction in diameter was only done over about 2/3 of the nozzle's length. The reduction in volume is therefore less... I didn't compute that.]
[Edit 2: Assuming 2/3 the length of the original nozzle was reduced to 0.8 mm, and the bottom 1/3 was left at 2 mm, the final volume would be 0.16{(2V)/3)} + V/3 = 0.44 V or 44% of original volume.]


Last edited by wstrohm; 09-02-18 at 01:25 PM. Reason: Variation in diameter noted.
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Old 09-02-18, 01:01 PM
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Originally Posted by wstrohm View Post
In any case I am inclined to accept TomU's advice to continue premixing... just because.
the cool thing is that if you miss a tank here and there its totally fine
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Old 09-06-18, 09:17 AM
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I wouldn't worry about it. If it's not in limp mode, you're fine.

A large portion of the oil consumption in the rotary engine is from oil leaking past the oil and gas seals, based on Mazda's study on the Rx-8. So it makes sense that a new engine with the new orifices would consume far less oil.
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