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OMP Declassified (tying up loose ends)

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Old 12-01-11, 08:33 PM
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OMP Declassified (tying up loose ends)

I thought I would wrap up some work I have been doing on understanding the OMP. This is the last in a series investigating the Oil Metering Pump.
See FYI:
https://www.rx7club.com/showthread.p...P+declassified
https://www.rx7club.com/showthread.p...P+declassified
https://www.rx7club.com/showthread.p...P+declassified

OMP and Oil mass delivery algorithm
In doing quite a bit of data logging and some chassis dyno time I have basically unraveled the algorithm the ECM uses to determine the amount of oil the OMP injects into the engine. Below I overlaid the output in volts of the OMPís position sensor with a curve based upon engine sensor output variables (specifically RPM and intake manifold pressure). You can also see a second to third gear shift in the graph with the corresponding drop in engine load. Incidentally, if the engineís torque curve is overlaid with a curve that is derived by multiplying RPM and Intake manifold pressure the curves would be virtually identical. This validates that engine load profile can simulated mathematically by using RPM and manifold pressure. So, in one extreme the engine could be turning 3000 RPM with high manifold pressure and be injecting a lot of oil and conversely the engine could be turning 9000 RPM with low manifold pressure and be injecting the same amount of oil; itís all about LOAD.



Limp Home and the Mazda ECM due to OMP indicated failure
The factory ECM continuously monitors the OMPís output position sensor (VMOP); it compares this voltage to an expected value based upon what the ECM has set the pump volume at via the stepper motor in the OMP. If the expected values do not match within a tolerance the ECM sets the OMP to the minimum oil injection value and the car to a limp home mode. I have tried to understand why a minimum oil injection value is set rather than a safer maximum value but can only surmise it is for emissions reasons.

The fatal flaw with the PFC
The OMP is a highly reliable component and physical oil injection failure is virtually nonexistent. If one has the opportunity to utilize the Mikuni OMP found in the Series 6 and later FDís, reliability is even higher. Regardless, oil injection is critical to the lubrication of the engine combustion chamber seals. Without additional oil the engine will surely self-destruct. With that said, a failure in the OMP will go virtually undetected with the PFC as the ECM. I have tried to induce the Exhaust Overheat light by disconnecting the OMP electrical but doesnít seem to come on. For those without a PFC the Exhaust Overheat Light is used as the Service Engine Soon indicator. Consequently, there is risk, a minimal risk, but still a risk. I have resolved and would recommend to periodically review data logs to ensure VMOP is changing with engine loads as it should.

Oil Injection Essentials
A significant component in the health of the oil injection system is the oil delivery lines, check valves, orifices, and air source. One area I have seen that would be of concern is loose bayonet fluid fittings. The total volume of oil flow is very small and a leak at a fitting would starve the critical oil to the engine; if there is an oil film or visible oil at the bayonet fittings get it fixed; maybe simply tightening the fitting. The second and probably highest failure rate component are the little check valves that thread in above the orifices in the rotor housings. If these check valves fail and they do quite often the oil will be blown into the primary turbocharger compressor inlet (if you have the stock configuration) rather than injected into the engine. I believe this may contribute to more engine failures than many other things. I would consider the check valves a standard replacement item whenever the engine is apart. Lastly, the air supply to the check valves must be filtered clean air. The check valves are sensitive to dirt and contamination and will not close properly if there is dirt on the seat. Also, the metering orifice that is pressed into the rotor housings is very small and with oil on it dirt can easily accumulate and plug the orifice again closing off or restricting the oil flow into the combustion chamber.

Hopefully this is a benefit to the groupÖ.
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Old 12-01-11, 08:54 PM
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Originally Posted by ttmott View Post
ssions reasons.

With that said, a failure in the OMP will go virtually undetected with the PFC as the ECM.
+1. This is why i leave my stock clear OMP oil lines exposed so that i can see the oil flowing from time to time and make sure the OMP is working, so with that said I never realy understood why guys get stainless steel OMP lines. Here is a video of my lines, i was playing with he vaccum to the oil injectors you can see the oil fluctuate..

http://s705.photobucket.com/albums/w...t=df9e716a.mp4
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