I have always felt that my '8, for whatever reason, consumed way less oil than it should for the kind of driving I engage in. After three different motors (each with a different OMP) and a string of PCM recalibrations, the oil consumption continued to dwindle to the point where, as it stands, my motor consumes no oil at all.
Now, I pre-mix fairly heavily (8 oz pr 14 gal of fuel, about 220:1), so I have been banking heavily on the insurance this provides. However, I was looking to discover a means to get the OMP to deliver more oil than it has been on its own.
I took apart one of the spare OMPs that I have laying around.
The OMP has a stepper motor that drives a geared cam that is regulated by a position sensor (interestingly enough, it is a throttle position sensor from the KL series of motors used in the MX6/MX-3/626/929/Millennia). When the PCM commands the valve open, it rotates in a counter-clockwise direction in a series of steps that are regulated in a servo motor fashion from minimum to maximum. This rotation turns and internal cam which, in turn, pushes open a set of spring loaded needles which have a "step" machined into them to allow a small amount of oil to get by (under pressure from the engine oil pump) and out to the metering nozzles.
Racing Beat provides a service where they enlarge the notch on one of the metering needles so that, when the needle is in its maximum "out" position, the amount of oil it delivers is greater. The two drawback I see with this are 1) They charge and exorbitant price for this service ($275) and 2) it only affects oil delivery when the OMP is at maximum.
What I am going to experiment with is adjustment of the position sensor
There is a lot of travel remaining in the "increase" direction (counter-clockwise). It seems to me that by just tweaking the position sensor a hair in that direction, one could increase the flow of the pump somewhat.
Phase 1 – MOP Basic Data Gathering (see post #1 for views)
Number of teeth on pinion gear: 16
Number of teeth on sector gear: 40
Degrees per step of stepping motor (pinion): 11.25 (1.5 times the original guessed value of 7.5)
Gear radius ratio (sector/pinion): 10 (actual best estimate 9.93)
Degrees per step for sector gear: 1.125
Mechanical Stop Thread size: 4-0.7 (4mm diameter, 0.7 mm pitch)
Equivalent steps for one turn of stop: 3
Total angular range of sensor: 19 degrees approximately.
Specific to the used MOP I acquired
Step number when sensor switch opens: 55
Steps before sector gear disengages from pinion: 72
Steps available before disengagement: 12 (assumes maximum steps commanded by PCM=60)
Number of turns of stop to cause disengagement: 4 (12/3)
Available range of sensor in counter-clockwise direction: 10.5 degrees approximately
Equivalent steps for this sensor range: 9.3 (10.5/1.125)
So it would appear that (but subject to further testing)
For this pump, the maximum number steps that can be introduced as a bias is 9, corresponding to three turns of the stop screw, and a complete counterclockwise rotation of the sensor. This might increase the steps to trigger the sensor switch by one (step 56) and it may throw a CEL. However from what appears to be known (OK if switch on between step 53 and 60) and what has been seen before, this is just a warning, and clearing it will cause the PCM to relearn the new position.
I made the rig shown in the picture using a cardboard box, freezer-wrap paper (writing on bottom of box still comes through) chopstick, sharpened nail, a couple of strong paper clips, and two SPDT switches. After wiring to the connector, I applied voltage and manually operated the switches to guide the current through the coils in the sequence needed to step the motor. The markings were put on after each step. The rig will be useful for observation in the vehicle, but I won't be able to get to that for a couple of weeks.
Yellow = A1
Red = A common
Blue = A2
Black = B1
Pink = B common
White = B2
Sensor Switch pin 1-3 normaly closed but open at "max" flow.
Very, very interested in motor position observations reveal during your road testing.
I determined that if the OMP position switch isn't turned far enough clockwise into the switch position range it causes the the PCM to go into the fail-safe/limp mode with no code. The condition is that on start up you have throttle for several seconds until the PCM decides there's an OMP issue, throws limp mode, and then you only have 11% throttle/4500rpm max in neutral. It stays in limp mode until you clear the PCM, but this situation will repeat until you adjust the position switch to the point the PCM is happy. This is an issue encountered by dannobre and several others and there's nothing in the service manual about it. The confounding part is no CEL code
and now you know the rest of the story …