Finding a direct replacement, and/or helping people find one who truly need one is helpful. It is not helpful in not redirecting guys like Bose and McKennaR who are obviously on the wrong track in search of alternate sensors.


Hopefully these comments will also be helpful:

- Don't waste your time measuring resistances and the like from sensors that look similar. They are usually variable resistances. Even if they were on/off switches, the switching position on the OMP is very specific to the RX8.

- If you believe your sensor is bad, test it by placing an ohmmeter or other continuity device across the pins and rotating the shaft engagement until it changes state (conductivity/no conductivity). You may hear a click. You can probably rotate it while still engaged to the shaft after removing the attachment screws.

- If it is electrically defective, why not try a DIY repair job? That would be helpful even if unsuccessful by at least documenting what you found inside.

 

As Delmeister has repeated ad-nauseum, our MOP sensor appears to be an on/off switch, not a potentiometer or variable resistor... unless the one I tested was broken, which I doubt.

I removed the bolts holding the switch onto the MOP and rotated the switch by hand clockwise when viewed from the switch side of the MOP. To keep the probes in place during all of this rotation, I used a spare connector and back-probed it.

Throughout its sweep of approx 90* clockwise, I got a constant continuity between the two outer pins up until I hit approx 70* of rotation. From then on the circuit was open until it wouldn't turn by hand any more at 90* from the start point (roughly). The center pin is a dummy, as even when I applied voltage, there was no measurable output from this pin as there would be in a potentiometer.

For kicks I measured resistance all the way until it hit open circuit to see if it would increase in a linear fashion until the circuit opened as a variable resistor would.

It did not. FWIW, it was around 60 Ohms with a "jitter" of +/- 15 ohms while the rotation was in progress. If I stopped the rotation, resistance would return to ~60 ohms.

Conclusion: It's an on-off switch with "on" (complete circuit) being the first 70* of rotation and "off" (open circuit) being the last 20* of rotation. Roughly.

Now, a question:

Does the RX8 PCM care what the resistance is when the circuit is closed? Are there any tolerances there?

 

PS. The reason I was barking up the physical dimensions / fitment "tree" is what's the point of digging around the internets for a switch that's electrically identical but physically different and thus won't fit?

 

When you are looking for an open/closed state, and an open state is millions of ohms, then 60 ohms, or several thousand ohms for that matter, is essentially zero ohms, or closed. You always have to allow for switches having some variable contact resistance. As in digital electronics, you never have pure 0 and 1 state signals. Anything between, say, 0 and 0.3 might be considered a 0 state, and anything between, say, 0.7 and 1.0 would be considered a 1.

Once you understand its unique electrical characteristics, you would appreciate the near impossibility of finding an alternative with both electrical and physical matches (if you found one you would have found the switch, not an alternative).

 

I sifted through this thread but never got the answer I was looking for .


Does anyone know if Adjusting the OMP ECU settings above the factory max. of '60' , will actually increase the flow ?

 

supposedly it can go as high as 70 or 72, saw it somewhere

also thought it said you can go too far, like it unscrews or something, so I just never went past 60

 

Looking a the first photo on this thread you can see there is maybe another 10-15% of rotation available before the pinion drops off the wheel.

But do we know that it will actually flow more when adjusted to say 70 ? The cam that determines how much stroke the pistons have will have a max. position as well.

 

No it won't. I studied that thing extensively and here is a plot of my data.

 

racing beat played with a modification to increase flow some years ago--but stopped offering it shortly afterward.

 

Delmeister seems to be the only one with a straight up answer ... - Many thanks

 

he was the one I was working from memory on

 

Unfortunately, I didn't check to see if the pinion would re-engage the sector gear after disengagement. And at the time I had the means to drive the stepper electrically on the bench. I didn't understand the interconnected relationship at the time and was concerned that disengaging the pair would throw the relationship off. It would not have. Later I forgot to test it.

 

if it doesn't flow any higher after 60 steps as you stated/tested then there's no point going there

 

Correct. It's just curiosity.

 

I just got my rx8 running but goes into limp mode looked under hood and my mop sensor is missing anyone have a extra one laying around?

 

Say what?
If fell off?

Should be a large oil leak there I would think?

Are you sure it's the MOP?

 

There won't be an oil leak, but losing a sensor has got to be a first.

Club member ayrton012 had one. You can try to PM him, although he hasn't been active for a couple of months.

 

yeah got the car not running, as a project it was a auto converted to 6spd
bypassed the clutch neutral safety switch got it started drove it 20ft and then went into limp mode opened hood and saw the mop position sensor wasn't there.
oil doesnt leak cause its just position sensor

Ok ill try to contact him thanks for the help

 

where are you located?

I've got a spare. In Ontario Canada

 

im in san diego California would you be willing to ship?
In the fsm wiring diagram it shows it as being a normally open switch
has anyone measured the value at what point the switch is closed?

 

IIRC, the switch changes state around step 52. It has some slop, the computer just wants to see something happening around there.

Your best bet is to just set it at the adjustment mid-range and see what happens. The first post shows the sensor is turned slightly clockwise. I've seen the same thing in other pictures. Ideally, you want to be around the middle of the acceptable range.

IIRC once the computer accepts the step number of the transition, it does not check again for a few driving cycles - I believe 12 or so. Therefore changing the sensor position looking for an optimum may not make any difference immediately. Disconnecting the battery after each change may force a check of the sensor position.

 

It does the check every time the car is started...so if it is out of whack it will limp mode on you quickly

What I have found works the best is to turn the stud on the pump clockwise till it stops...set the switch so that it just engages the switch....and that seems to work. If not...just move it slightly and check it...reset the ecu..start the car and after about 30 sec if you still have throttle it is good. If not...turn it a bit more....etc until it works

Sometimes it will work and then fault...just a tiny bit more and you are golden

 

Take a look at the attached page from the factory manual. See the numbers 52 and 12, and the reference to the battery?

 

Could be...but if it limps it will do it every time you try a reset...so effectively the limit is useless once it faults.

 

Could Be? Have you got a better source?

Of coarse if it goes into limp mode it will stay in that mode until it gets the acceptable number of steps. You can make adjustments here and it will check after each ignition cycle. That's a given and not what I was talking about.

I said that once you get it to accept a position, you can disconnect the battery and make another adjustment in the process of optimizing the position. It will then do a check on the first ignition cycle after a battery reconnect. Otherwise it will check on the 12th cycle (and maybe fail you if the position is right at the hairy edge, and you are far from home).