MOP Adjustments
 

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.

https://www.rx8club.com/attachment.p...1&d=1182492219

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.

https://www.rx8club.com/attachment.p...1&d=1182492219

https://www.rx8club.com/attachment.p...1&d=1182492219


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.

Any suggestions are welcome.

I would start with the position sensor first like you suggested.
Like the KL Tb's is there a voltage reading that can be adjusted?
Would different spring rates affect the oil flow, more or less , sooner rather
than later.
And of course the more difficult one would be to have access to a lathe and
machine the pins a couple of thousandths. that is if you knew where on the pin
to machine.
You could put the pins in a dremel and use some sand paper. not as accurate but could also get it done.

Andy P. 93 GS 1.8T

From what I read the new flash increases the flow through the OMP.

If that doesn't solve the problem, then how about having RB reprogram it for you?

The set srew adjustment will just affect the oil flow at idle.

The sensor position is just like points right?

Changing that will only effect how fast it reacts, not increase the flow, Right?
Move points closer or farther out. Changes timing not flow.

Look at the needles. They are like motorcyle carbs. We have adjustments to increase flow.

You can create a notch in the needles.

Then you can lower or raise the height. Effectively chaging the flow throughout the whole range.


I think we need to look at the mechanical side and modify the needles.

You can put a notch in it to move the washer on the end to compress the spring more.

This is what I am thinking. Remove that washer on the end and use C clips like on motorcycle carbs. Make two more notches and you have something to play with.

Another way to cheat is to take the needles and regrind them. Make the taper differant. By reducing the thickness and taper you will flow more oil.

What do you think?

The position sensor tells the PCM at what position the volume cam is pointed.
Turning the sensor counter-clockwise will tell the PCM that closed is a actually little more open. It will also tell the PCM open is wider than it thinks.
The overall effect is that the range of the cam will be moved up scale. More oil will happen everywhere.

In theory, anyway.

I'm getting under there to adjust my wastegate tonight, so I'll take some scope measurements and twist it open a bit and see what happens.

I don't know anything about this particular stepper or what kind of PWM signal it's receiving, but theoretically speaking, you could put a device between the stepper and stepper controller that altered the PWM signal delivered to the motor itself to drive it to whatever position you wanted.

You'd also have to alter the signal sent back to the controller from the position sensor so it doesn't think that it's too far open. You could keep all of this in a pair of lookup tables.

Of course, adding an electrical device to the loop has its own risks and issues.

Someone here actually hooked up a second OMP that the PCM controls directly so it stays happy.
Then, you could use a stepper driver to alter the signal and drive the original motor however you wish.
That does add way to much complexity, though.
It think just altering the feedback signal will do the trick.

You've got to be careful with that though as you don't want to force the PCM to drive the motor too far or it'll be grinding up against the end of the travel, which could be potentially damaging, otherwise, I would say just put a voltage divider circuit on the output of the sensor to make the PCM think it wasn't delivering enough...

Well, looking at the pump I dissected, there is still a whole bunch of travel left at the open end.
The closed end has a stop screw.

Great info MM!!

I am going to look at the position sensor rotation as well to get the OMP to flow more throughout the range - great research!

Also, you may have discovered why so many people are running different rates - since the position sensor is adjustable, could be that they are set differently for some people.

is the stop screw adjustable--i am thinking it is? if it is --well hell--turn that damn thing! Shouldn't take much
olddragger

it will, hopefully enough. its like adding a washer or 2 to the mechanical ones.

I checked my oil level today and it actually changed from last week. Perhaps my OMP decided to just turn on all of a sudden. Werid. And of course it happens once I start to premix

I'll crank it on Monday night while I'm doing other stuff.

How is the calibration done for it? The sensor output would be different for each car, I would think it would move to the hard limit, and 'zero' itself from there.

Or is it like an inhouse factory done thing?

Thanks again for the info and ideas MM!.

So today, I adjusted my OMP position sensor as MM suggested. Here are my notes:

- It is easy to loosen the two screws from underneath and adjust the sensor. There appears to be about 30 degrees of movement possible in the counter-clockwise direction (more oil flow) and none in the clockwise direction. I used a 7mm socket instead of a screwdriver as it easier to reach with extensions through the fenderwell this way.

- I first moved the sensor as far counter-clockwise as I could for maximum oil flow - about 30 degrees. Unfortunately, this threw a CEL immediately upon starting the car and put the engine in limp mode as I suspect it took it slightly out of the normal adjustable range.

- So, I disconnected the battery to reset the ECU, and then backed the OMP sensor back (clockwise) about 5, maybe 10 degrees. This time when I started the car, all was well with no CELs. I took a short drive, about 5-10 miles, and it seems to be fine.

Now the fun part is to start monitoring the impact to OMP oil injection to see what the difference is - I an currently using about 1 qt/3000 miles (slightly more miles than I previously thought). I hope this increases the OMP flow significantly - I would like to see 1 qt/1500 miles to reduce my premix need, but we'll see.

I will provide usage data as I collect it.

Cool.
I'm under my car right now, doing a compression test and a de-carbon technique to measure the impact. I'm also fabbing my oil cooler fan brackets since the fans showed up last week.
I'll probably twiddle my position sensor around 10 degrees or so and see what happens.

You might want to pre-mix during the experiment just in case it doesn't go as planned.

I am still premixing 3oz if IRP with 2oz FP3000 per tank and will continue until I see proof that this adjustment has increased the OMP feed and I have calculated a new average feed rate.

I agree with your assessment though on the OMP operation and I don't see how this mod could flow less oil (although anything is possible I guess), but we just don't have any way to really know how much more it will flow with the adjustment as the ECU might pick up this change and just compensate for it (hopefully not though).

ecu does a self check of the mop periodically, its possible that you turned it too far, but that once it rechecks and rezeros itself you can go further

Let us know how the fans work out, I have been thinking about doing that also.

My electrical schematic shows that the sensor is just a switch. If that is the case then what probably happens is this:

At ignition on, the stepping motor backs off until it hits the minimum stop. It then reverses and counts the steps until the sensor switch changes state. At the factory, the sensor was positioned for X number of steps to the switch. Some allowance is provided in the programming to account for movement in this adjustment as a result of wear, vibration, etc as the vehicle ages. However too far a movement and a flag is raised, i.e. CEL.

My guess is that if the PCM does not get the correct number of steps, and if the error is not too great, then it will simply assume there has been a slight movement of the switch, and do exactly what it did before the switch was moved. That is it will provide the stepping motor with the number of pulses it is programed with to meet the lubrication requirements of the engine. The sensor is just a check that things haven't gone too far astray.

If you are correct and the ECU does not compensate the OMP base flow rate position based on the readings back from the position sensor, but just uses it as a relative position check, then moving it will not have any impact on oil flow at all.

While this is possible, I am hoping it is not and that the ECU will adjust the base rate setting based on the adjusted position sensor - we'll see.

could it be that your driving results in more blow-by and fuel dilution and making it appear as the oil level never goes down?

in some turbo rx-7's the oil level actually goes up!

can the set screw be moved? Do we want too?
olddragger

if you were to separate the 'saw arm' from the gear it meshes with, couldn't you turn the gear slightly (and then put the saw arm back in the same position) to pre-load the amount? then it would always be at a higher setting than it used to be (across the range). I'm assuming that simply adjusting the stop screw is not giving enough extra flow (or it can't be moved). The only danger here would be if it tried to move beyond the full flow point and the omp has a bad failure mode in this case (doesn't stop at max & something bad happens).

$.02

this is interesting to follow~

makes sense, would have to be very careful about how much to turn the set screw---IF it is adjustable--which I kinda think it is not. Moving the sensor as stated may be something of interest!! I have one of those cars that doesnt use oil unless i am on the track.
olddragger

The set screw controls minimum flow. It is adjustable, but I don't know what the net effect would be.
The relative saw arm to drive gear position is irrelevant since it is continuous. It is the servo function of the position sensor that gives it meaning.
The position sensor is not a switch. It is a pot and provides a position feedback function to the PCM.

I wish the damn OMP was in a more easily accessed position so I could play with all of the possibilities without hurting my back.

true that the position sensor gives it meaning, but wouldn't adjusting the saw arm or gear independently of one another skew the actual setting? it would mean that when the position sensor reported to the ecu that the mop was at setting "1" it would really be set to "2"...?

No, it would just continue to turn the motor until it hit the stop screw and set that position as zero.
This is why it is a long shot that setting the range of the position sensor to something higher than the OEM setting will yield a greater output since the PCM calibrates minimum on its own.
Perhaps a greater stop crew setting coupled with a position sensor turn is required for the desired effect.

What is this thing then?

That is the position sensor.
I don't know why it is labeled a "switch" on the diagrams, but it is a pot and passes a variable resistance based on position.

If the PCM only uses this resistance to show that the OMP has moved off of its stop, then it will be useless as an adjuster.
However, the tech training material refers to this system as a servo, which means a full-control feedback loop.

Wanna share with me/us?

hello? no one thinks this makes sense?

Neit....
 

....my level rises slowly for the whole period between oil changes.

(....but I DO pre-mix heavily.)

S

Not really.
Take a look at how the rings and seals on the rotors work in conjunction with the ports.
For blowby to substantially raise the oil level on the Renesis would require almost a complete failure of the cutoff ring.
People that are exhibiting an increase in oil level during normal operation are experiencing something else.

My theory is condensation - at least for Stealth. Since he is in the "waaay North" with generally cooler temps, he may not really ever get his oil that hot, which will cause some collection of moisture over time in the oil and cause oil levels to stay the same or actually rise (or appear to due to the added moisture).

Example - For someone who does a lot of city driving; ever notice the oil level never dropping (or very little) looking like you don't use any oil; and if you take a long trip (3-5 hundred miles - or track the car), that at the end of it it looks like you used a lot of oil as your oil level has dropped a bunch (a quart or more); that will be mostly from condensation burnoff with less than thought actual oil usage. This occurs because mostly city driving never gets the oil hot enough, long enough, to get rid of the moisture and provides the appearance of no oil burning or actual gains until you do a long trip or have a track day to burn off the moisture that collects.

This is just one of the reasons that it is very difficult to accurately measure oil usage in an 8 unless you have a separate tank - and even then the oil in the tank can collect some moisture over time if not used timely.

Possibly, though a lot of water accumulation usually shows itself as spooge, rather than fluid.
I don't have much experience with those kinds of temps and humidity. In Maryland, I never experienced that, though.

all of this is of great interest---i wonder why racing beat went the way it did on omp modification. Do they know something we dont? Probably. Do the good folks working with this know something RB doesn't----maybe.
Would it be easier to just do the mechanical thing with the jets?
olddragger

Well, I think the idea with RB is to just increase the flow in the high-load regions and leave everything else unaffected.
This would make sense, if the OMP is working the way it is supposed to.
I contend that mine is not.

bingo Ray you are reading my mind. i am much more mechanically minded than electrically minded anyway
olddragger

Ray's solution is most likely the best.
I am just looking to get my OMP to deliver that "advertised" amount of oil.
Really, I'd like to see it deliver ANY oil.

if you run the older turbo engines rich, and dont have a good pcv setup, the oil gets diluted with gasoline, and the level on the dipstick will stay the same or go up slightly. the extra cutoff seal in the renny, in theory fixes this

Plus, any blow-by on the compression stroke is going to go out the intake port and any on the power stroke will go out the exhaust port.
Those are uncovered by the side seal as it goes by. One or the other is almost always "open" inside the side seals.
Only at TDC are no ports available to the sides of the rotor.
At the point of maximum dynamic pressure, the exhaust port is exposed to the side of the rotor, inside the side seal.

In any case, assuming a working MOP, and even given the possible differences from car to car on how much oil is actually delivered on an absolute scale, it sure would be neat to have a sCANalyzer or electro-mechanical gauge to see MOP performance in real time wouldn't it? Any 'tappable' PCM signal available to feed such a gauge or gauge driving circuit? Just brainstorming...

There is nothing actually "measuring" the amount of oil going in.

All the PCM knows is the position of the stepper motor in the pump. It would be nice to know actual flow values.....


And even nicer to know the load/?? values the PCM uses to decide how much oil to inject.

Maybe the Cobb guys have had a look at that table :)

Understood, but if you knew your OMP was at least working (whatever you guys determine that means flow wise) wouldn't it be nice to know what it is doing (or trying to do) on a relative scale?

-C

From the information provided so far, it seems that to get a higher flow without maching things is to:
- crank the stop screw down so that the reference zero is at a higher flow,
- rotate the sensor the same effective angular distance in the same direction.
As far as the control system is concerned, nothing has changed but in reality there is an offset to higher flow for all position settings.

How much oil flow is involved? In a steady run, say a liter is burned every 1800 miles. Traveling at 60 mph, that's about 0.56 cc per min. If the gas milage is 4 liters per 20 miles, 360 liters of gas would be consumed which is the gas to oil ratio.

It would seem almost impossible to blindly control (because there is no feedback on actual flow) a flow of a few drops per min through a needle valve under engine pressure (~50psi). The actual orifice size must be really small and any change in this (dirt, wear) could greatly affect flow. Also because the oil moves so slowly, it's temperature must be more reflective of the engine bay temperature rather than the temperature of the engine itself. The oil viscosity changes significantly over the ambient temperature ranges these cars can operate in, and so presumably would the flow characteristics.

Maybe the flow is on/off rather than steady. For one thing it would help clean out any debris.

Theoretically......
 

It is still only a theory that the servo takes a "reference zero" from the stopscrew......it has never been observed, nor is there any evidence of the ECU self-calibrating the sensor in that fashion.

.....it's just a theory until someone 'scopes it in action.

S

exactly stealth--no proof yet but a dang good progress to better understanding and possible fix. I am cautiously optimistic that the set screw thing may work to a certain degree. I will not have time to fool with this until almost august
olddragger

How many options are there for the ECU to know where the sector gear is in real terms? It can't be the sensor because the sensor gives position relative to the sector gear. Do you think it is in silicon memory - that from the day the car leaves the factory, to 20 years hence when it is junked, it will rely on remembering how many steps the motor was delivered, given all the electrical glitches and possible missed steps along the way . Obviously not because there would then be no need for a position sensor. The only place left is the mechanical stop, the only reliable place to get a reference.

Although not entirely relevant, as far as I know all stepping motor systems have a home position for reference.

Edit: The comment I made about the sensor is incorrect. Once fixed to the frame, the sensor indicates absolute sector gear position just as the stop screw does. It's primary drawback is that it is electrical and more easily displaced than the stop screw. Movement of either one gives indication of position from the new location. Move them both the same amount in the same direction and the ECU doesn't know anything was changed (I think).