OMP Declassified Part III (the Mikuni)
 

In the last OMP Declassified the Denso OMP oil flows were evaluated; in this post the Mikuni pump is evaluated. The Mikuni is much different than the Denso as it has two oil pumps (one large and one small), the stepper motor is rotary in contrast to the Denso's linear motor, and the position sensor is a rotary potentiometer rather than the Denso's linear sensor. Below are the two pumps side by side:
https://www.rx7club.com/picture.php?...ictureid=22829

Drive Side View:
https://www.rx7club.com/picture.php?...ictureid=22830

The following picture shows the Mikuni OMP disassembled. Note the two oil pumps (one large and one small)
https://www.rx7club.com/picture.php?...ictureid=22835

The next image shows the Mikuni pump stroke length means of adjustment and the position sensor:
https://www.rx7club.com/picture.php?...ictureid=22833

The two pumps can be switched from the drive side of the pump housing to the port side of the housing. The drive side rotates at one half the speed of the port side and the stroke length has a different profile and length between the port side and drive side. So one could swap the two pumps and obtain higher flow at low engine RPM's and lower flow at high engine RPM's or Lower flow at low engine RPM's and higher flow at high RPM's. The factory arrangement is the latter.

The following data provides the Port side pump flows by stroke length and position sensor output in Ohms. Note that I have given flows for both the small and large pump in the Port position.
https://www.rx7club.com/picture.php?...ictureid=22832

The next set of data provides the Drive side pump flows by stroke length and position sensor output in Ohms. Again I have given flows for both the small and large pump in the Drive position
https://www.rx7club.com/picture.php?...ictureid=22831

Now below shown is the data put together including output by E-Shaft revolution:
https://www.rx7club.com/picture.php?...ictureid=22834

The following chart puts the above data in graphical format. You can see the two different profiles that can be created by swaping the pumps. The Red and Brown lines are by pump drive revolution at different stroke length settings in Ohms and the Blue and Purple lines are by E-shaft revolution by stroke length setting in Ohms:
https://www.rx7club.com/picture.php?...ictureid=22838

For flows by pump stroke length and engine RPM the following maps are given (blue map has small pump on drive side and large pump on port side and red map has large pump on drive side and small pump on port side). The corresponding graphs are for each map:
https://www.rx7club.com/picture.php?...ictureid=22840
https://www.rx7club.com/picture.php?...ictureid=22837

https://www.rx7club.com/picture.php?...ictureid=22839
https://www.rx7club.com/picture.php?...ictureid=22836

Looking at the flow rates from the Denso and Mikuni pumps if the Mikuni pump is set up at the higher flow rate (factory setting) the Mikuni has about the same oil delivery at low engine load settings and significantly higher oil flow at the higher loads which makes the Mikuni probably a more desireable pump. There is a glitch in using the Mikuni in the 93 - 99 FD's; that is the position sensor will output different voltages from what the PCM is looking for. The Denso position sensor is 500-1800 Ohms and the Mikuni is 500-3400 Ohms. I have heard these can and have been used interchangeably but it appears for the Mikuni the PCM for the 93 - 99 FD will look to set it at 1800 Ohms at idle which will set a very high oil flow at the lower engine load settings; this is speculation on my behalf. Hopefully, someone who has been running one of the Mikuni's can chime in.

Great info, thanks for sharing. I suspect if you were really interested it may be possible to trick an ECU into using a Mikuni pump, but is that necessary for the PFC? I'm assuming that if you need the additional oil injection the stock ECU isn't going to be sufficient in terms of fuel and spark.


Have you also measured pump flow rate to back up your calcs?

how did you even get your hands on a Mikuni pump?

I assume they'll show up every now and again off used motors. Wouldn't mind having one myself, I'm sure they're CRAZY expensive new from Mazda Japan and I'm sure they'd be hard as hell to find used.

Regardless, EXCELLENT info, BIG THUMBS UP for taking the time to plot this out!

I'm not totally sure if the PFC will even care that there's a difference in the pump. Stock ECU might pitch a fit, but if you're at the point in modifying your car that you're thinking about swapping the OMP out, you most likely have a PFC at that point.

Dale

+1

reverse engineering factory stuff can be fun. it really forces you to think and do research.

So mazda thought the oil injection should double?
Is that why they switched over to the muniki?
or was it because the increase in Horse Power in the latter FD that they increased the omp flow?

Also whats up with the difference in the reservoir? are the latter FD front cover different?


http://i705.photobucket.com/albums/w...beoner/omp.jpg

Didn't flow oil but the pump is positive displacement so the calcs should be close.

Japan2LA sent it to me. He is one of our club vendors; great to deal with and excellent parts resource.

Looks to be only a difference in machining; will align with the cover OK.


Looking again at the position sensor and the difference between the two, it looks like they may be interchangeable:
https://www.rx7club.com/picture.php?...ictureid=22889

Nice work, ttmott.

Here's a little tech info on some of the changes to the version VI (99-02) engine, taken from an SAE article:

Great work. If I had known about the Mikuni, it would have saved me all the headaches of custom made oil return line, fittings, adapters and the like in order for the RA OMP adapter to work.

As others have said, thanks for the information. I don't have the engineering background like some but it's still fun to try and follow.

Thanks for the great info.

So has anyone actually tried this? Do you need to run the newer/smaller injectors to run this pump? If I have a Power FC, it'll just plug right in and not throw any additional lights?

Not sure if you MUST change to the later injectors with the Mikuni. I have read reports of the the new(er), smaller diameter injectors plugging-up over time. Other than the smaller port, it wasn't clear why. It may have simply been from poor scheduled maintanence.
And yes, the PFC does not throw CELs and won't care what OMP you have. It won't even care if the OMP is working, or there at all. Because of that, even with the OMP some pre-mix a little to augment.

Shouldn't throw codes with a stock ECM either based upon it's VMOP output of about 1.1 to 4.1 VDC (See my previous post). The resistance measurements across the stepper motor is slightly out of family (~35 ohms vs. 16-31 ohms spec.) for the 93 to 99 but it shouldn't be a problem. I have a PFC so can't really test it in a stock configuration.

The injector port size was reduced (see Gomez's post above) to solve a technical issue regarding the engine vacuum non-boost modes from sucking the oil out of the injector cavities then during accelleration having no oil until the OMP could catch up. Most of us have the rubber filler under the check valve which should solve any potential issue in the oil refill lag with a large cavity. I don't believe we really had issues with the Denso pump and larger injectors so if you run the Mikuni pump you definately would not have any issues.

I have installed the late omp model(mikuni) together with the new injector grommets 3 years ago,with no problems whatsoever.Also,all the new mazda replacement housings come with the new grommets...

So I'm still not sure I understand the benefits of the newer pump as the signal values the pump is expecting (as you stated) has a different range for each pump style (new and old). Would you happen to have a flow curve for the denso pump to compare to the new style? And even if we CAN compare flow rates of the two pumps directly to one another, we still haven't factored in the influence of the updated nozzles, so we still don't know exactly how different the total flow per RPM is when you compare the entire package/setup (old vs new). I'm really interested in finding out however as Mazda seems to be heading down the trail of adding more and more oil (updated pump for 99+, rx8 gets two oil injectors, and supposedly the 16x will have 3). I have a hunch they know something we should know... but we still have to prove it.

Also, this kinda begs the question... what is on the 8? I know the 8 has two nozzles per rotor housing, so 4 lines total from the OMP. Now I'm curious :)

I think that is the omp unit he installed on my car. I was actually going to ask him what his thoughts are on this info.

As it ends up (see previous post from me) the VMOP is the same for both pumps so for the factory ECM's should not be an issue. For the PFC or other controllers the VMOP is ignored and the pump output curve can be changed in the software so again no problem.

I profiled the Denso pump in OMP Declassified Part II https://www.rx7club.com/3rd-generation-specific-1993-2002-16/omp-declassified-part-ii-895388/ so you could compare the two. If I have time I'll overlay the flow curves. The real benefit is the Mikuni can be set up to flow quite a bit more oil at high engine loads and pretty much match the Denso at low engine loads. I think they bring a lot to the table for those who do not want to premix and running chamber pressures higher than stock.

Tom

Thanks for the information! Yeah more oil at higher RPM's is a must... I'm just curious if it actually works out to more flow when the smaller nozzles enter the mix, but I have a feeling it does.

Also, looking at my 20b pump I believe its the same denso unit as the FD (but with a 3rd output). Now I'm interested in opening it up to see if anything is substantially different or just a 3rd port.

I am sure there is more to it than the 3rd port. The needle that fits inside sector valve / pump is probably a larger diameter for the additional oil volume required. Quite possibly also the worm gear ratio and / or the drive under the engine cover could be different. It would be interesting to add it to this data collection.

If it wont be destroyed by taking it apart I'm not opposed LOL Would give me a chance to clean out the internals

I have a question here... I took my spare OMP apart to mess around with it and i see that When the SECTOR VALVE NEEDLE is pushed all the way IN it cuts flow to the secondary hole in the SECTOR VALVE. Is it safe to assume that this secondary hole is opened up at higher rpms? If so what if i bore out the opening, will it increase oil to the housing injectors?

any thoughts?

sorry for the bad pics,camera phone...

Attachment 711925

Attachment 711926

I thought that also but a couple of things:
The small hole is drilled at an angle downward to as to not be in the area where the needle is.
The needle does not insert fully into the bore of the sector valve and it's maximum stroke is rather short; look at the height of the cams on the sector valve drive gears.
As the sector valve rotates the holes align either with the oil supply or the discharge ports.
Also as the sector valve rotates it moves up and down. The length of the up and down movement is dependent on the position of the linear (Denso in your case) stepper motor.
As the valve rotates and moves down the oil supply is open to the lower sector hole and the needle is retracted. This draws oil into the sector valve internal area.
The valve continues to rotate and then moves up in concert with the small upper hole aligning with the oil discharge port holes. As the valve moves up the needle is depressed into the sector valve forcing the oil out of the OMP and to the injectors.

you should try disassembling a series 5 FC omp. You can get them cheap. Those are the first electric OMP's to be fitted to an Rx-7. I wonder what the differences are between that and say these late model Mikuni pumps.

If someone will contribute one to the cause I'll set up and profile it's performance and add to this data. Same for the three rotor.... Taking them apart does no damage as long as they have been maintained well and the O-rings are still pliable.

same as the denso,, but 4 output ports