S5 omp

[Pete_89T2]

Originally Posted by tweiss3

Thanks, for the replay, it makes a bunch of sense. What does the feedback signal look like? I'm curious now.

If you reverse engineer the FSM test procedure, it's easy to figure out that the OMP feedback loop is implemented with a potentiometer that varies it's resistance based on the stepper motor's position. The problem is the FSM doesn't elaborate on what that resistance is for each of the stepper motor's 4 possible positions - all it does is give you some min/max resistance values to measure across the OMP connector terminals when it's in a static condition (i.e., disconnected) to judge it as good/bad.

Also, the S5 FCs, all FDs & FE's ECUs vary OMP oil delivery settings as functions of not just RPM, but engine load, and perhaps some other conditions depending on the model year/ECU version. Without knowing precisely how Mazda mapped this function into the ECU (which sensor inputs matter, under what conditions?) it makes it very difficult to come up with a good feedback sim/stim to wire in and fool the ECU to stay out of limp mode. To reverse engineer this, one way might be to get someone with the same year/model '7 that still has a working OMP, and rig up a way to measure voltages across the OMP feedback potentiometer on a running car with a high-impedance DVM (high impedance so you don't effect the system's operation or the measurement). Stick the car on a dyno, and start data logging those voltages as functions of everything else you can possibly measure at the same time (RPM, MAP, etc.). Then you would have to analyze the data and try to reverse engineer the resistance vs. OMP setting curve.

Another thought might be testing by substitution. Get same '7 with working OMP, disconnect the 3 pin OMP feedback connector (I'm assuming S5 T2, don't know if the OMP wiring is same on FDs & FEs), and replace it in the circuit with a fixed value resistor. I'm thinking you get a bunch of fixed value 1/4 watt resistors that range in value from the min to the max values listed in the FSM OMP feedback test, start at the low end and work your way up to the high end. At each iteration, go for a test drive that runs across the car's RPM range under different loads. If/when it goes into limp mode, record (1) the resistor value you used (2) At what RPM it went limp, and at least have an estimate of engine load when it went limp - if you can monitor MAP (i.e., boost/vacuum gauge), that will work - high boost = high loads, deep vacuum = low loads. Based on the data you collect, it might be possible to design a sim/stim box to fool the ECU.

Of course all this crap is very time consuming, so the most expediant fix is just replacing the OMP with used/new after verifying that your wiring is still sound.

[RETed]

If you still want to further pursure this...
No need to systematically map the E-OMP.
The map is given in an SAE paper somewhere...


-Ted

[Pete_89T2]

Originally Posted by RETed

If you still want to further pursure this...
No need to systematically map the E-OMP.
The map is given in an SAE paper somewhere...


-Ted

I do vaguely remember someone posted a 3-D surface plot from an SAE paper that had RPM vs. MAP/engine load vs. OMP oil volume delivered, damned if I can find it though.