My 90 NA with 236k and no driving issues before, has been sitting for around a year and finally taking it out a few days ago it goes into limp mode and throws on the celo under load. I had been starting it every other month letting it get to operating temp then revving it up and shutting it off. Checking faults I have fault code 27. Doing some searches I found either ground issue or mop and ecu. I found Arron Cake's page about engine grounds and cleaned and treated all the grounds described. Hoping since it was sitting that I had some corrosion, not the case not fixed. I also read that mop failure could ruin the ecu. I have another mop and plugged that in to see if it would fix it, nope...so before I buy an ecu, there is nothing I am missing correct? The only nice thing is it is easy to duplicate, rev out first or second and instant limp mode...anyway just seeing if I'm on the right track.

 

well according to the codes is should be OMP related,and it sure sounds like it is tossing it into limp mode.,

RX7 FD and Series 5 Error Codes

I'd look for another good electric OMP..(if you run the car in limp mode it can in turn take out the ecu.)..also keep that spare Ecu handy as I think the new OMP may be showing that the OMP did take the ECU out too.

 

Now I'm not sure how the mop works on the s5, since it's electric shouldn't the shaft spin when the car is running? When I plugged in the other mop I set it off to the side and expected to see the shaft turning when I started the car, but it did nothing.

In my mind this should be a way to test the system out. If I get a good ecu and plugging in a different mop, start the car should I see the shaft on the mop spin? Or are there other factors I'm missing? Also does anyone know how a mop burns out the ecu? Besides throwing out the ecu what can be done with the ecu, can they be repaired?

 

i had the same problem and i just put an rtek chip in it and premixed. Engine oil really isnt designed to burn up under combustion anyways

 

I was looking into that option too. Its either I get a used ecu and swap out the mop, cross my fingers that it works or for around the same money do the rtek ecu which will fix it. Don't know which is better disabling the system or trying to fix it right.

Then if I do fix it correctly how long do I have till it happens again. They are used parts being 25 years old who knows. Does anyone really know what causes this to happen. Does the mop just quit and back feed power into the ecu frying it?

 

The stepper motor shorts and it cooks the transistors in the stepper motor drive circuit in the ECU (usually). OMPs can fry for other reasons but that is the most common failure mode.

There is a position sensor on the OMP so if the drive circuit is fried and the motor isn't moving, the ECU sees that and still throws you a code.

Long story short, your ecu took a hit partner and you need to swap it.

 

The MOP is spun by the engine. There's a shaft in the front cover that spins it from the front rotating assembly. The electronic portion on the MOP only controls the amount of oil injected IIRC.

 

Yup, the stepper motor controls a valve and thus oil flow.

 

Great, thanks for all the info it is just what I wanted to know. One last thing, if I get the rtek chip can I use my burnt out ecu? Will the chip negate the blown transistors in the ecu or do I need to get another ecu and then do the rtek chip...

 

Ask the guys at pocketlogger, but I think they will retek that ECU effectively. I will depend of course if there is any damage unrelated to the MOP driver circuit.

If you go that way, let everyone know how it works out.

Good luck!

-Jack