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 OMP’s 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 engine’s 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; it’s all about LOAD.
https://www.rx7club.com/picture.php?...ictureid=22382


Limp Home and the Mazda ECM due to OMP indicated failure
The factory ECM continuously monitors the OMP’s 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 FD’s, 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 doesn’t 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 group….

+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

Some thoughts on OMP piping I didn't see listed elsewhere:
1) In addition to being opaque, the after-market stainless oil feed lines don't have the check valve at the top that the stock plastic lines. I'm guessing that check valve is there to help keep oil from draining out of the lines when the car is parked. The ability to see oil flowing in these lines does seem to be a useful way to check that the OMP is still operating. Although such an intermittent check doesn't seem like it would prevent engine damage. Anyway, after buying stainless lines, then reading here about the check valve, I decided to keep using the stock clear feed lines with the check valve.
2) Using the stock routing of the check valve vent lines to the intake might be better than routing them to the oil filler neck. If the check valves fail, there is at least some prayer that the engine combustion chamber will see some lubrication if the oil gets sucked into the intake, but no prayer if it goes back to the oil pan.
3) Here are three possible methods for making it possible to detect check valve failure, in addition to routing them to a separate catch can as others have done:
- Use clear silicone vacuum hose to route them to the intake. If the check valves fail, oil will be visible in these clear lines. HPS sells clear hose.
- If you don't like the look of clear hose, use opaque hose to route them to the intake but put a clear polycarbonate fitting somewhere visible in the line, such as McMaster 5117K97, so it is possible to see if oil is in the line (and thus the check valve has failed). Polycarbonate is a high temp plastic with excellent resistance to oil and gasoline, so should hold up.
- If you don't like plastic, plumb this inline brass sight glass into the line running to the intake - McMaster 5069K51. It is a little long at 2 1/4", but should be pretty sturdy.

I'm going to try the clear hose method.