Hello,

After a lot of false tries, I discovered my s5's problem was caused by the OMP going and causing the ECU to be damaged. I sent the ECU to a company in Floriday who diagnosed and repaired it ($240 w/ round-trip shipping). I know I could have purchased a used ECU, but I still would have been forced to run the full diagnostic on it, with no guarantee of it being good. This way the ECU is guaranteed to be A-OK.

My question is: Do a lot of people find that a bad OMP will cause this? I ask because due to the high cost of a new OMP, most people recommend going with a used one (tested first to be sure it works). If we are resigned to be installing used OMP's, it seems that after 30 or 40k, this problem might recur with a used OMP, causing another expensive computer failure.

Any thoughts?

 

I've heard of more than one person losing their s5 ECU because of the MOP.

 

it happened to me, i didnt have too much time to work on my car when it happened so it took me about a month to figure out the ecu was fried. its a really crappy thing when it happens, i dont understand why the omp fries the ecu when its broken, is it a failsafe to protect the engine or just crappy wiring design by mazda?

 

The OMP motor acts like a resistor in the circuit. When it fries, for a split second the ECU see direct voltage and more amps than it can handle and it fries it.

mazda SHOULD have installed a fuse in that circuit, and that may just be what is needed to stop the OMP from taking the ECU with it.

However, knowing that when the OMP goes, the ECU fries has got me more than one RX from a used car dealer that go shanked on a trade in for a couple of hundred bucks. Problem is, i think i've now snagged every good OMP from every bone yard within 75 miles, actually, my last resort last time was 98 miles away!!!

classic symptoms are, it idles fine, it will try to take off but when it hits about 3 grand it falls on its facec and the check engine light comes on and it won't run right again until you clear the ECU.

 

Yep, that was exactly what was happening to me. Thank God I had the car hauled out of the dealership when they told me $2200 to install an OMP. A lesser person might have okay'ed the work. Then they would have gotten the call afterwards that they also needed an ECU. I feel real sympathy for people who rely on dealers when they don't know their own way around an engine compartment. The upside is for a $90 diagnostic fee I also got an actual Mazda compression test, so it wasn't a total waste.

PS I'd be interested in any ideas about the in-line fuse.

 

so, being that the MOP is just a big resistor (per se) in the circut, couldn't you just unplug it and replace it with an actual resistor and not have any trouble codes, being that I am looking at pulling the MOP and switching to premix soon, and I don't want it just being there adding weight (can you tell I grew up racing?). If sombody makes this, let me know, otherwise I guess I will have to come up with my own ingenious idea (scary thought)

p.s. sorry to jack your thread, just trying to come up with ways to prevent this heartbrake hitting my wallet

 

No problem, the same idea occured to me since I switched to pre-mix and zip tied the new OMP to the strut tower. I changed the bad one once, with what turned out to be another bad one. I just didn't feel like going in there twice. We need a Radio Shack junkie to make some of these up. I've got $20 for the first industrious person to do this....

 

******* mazda...just reading about the omp gets me all fired up about it again. such a waste of money to fix it...

 

If i had an oscilloscope i could probably make something that would work. But if it's the motor that fries, then you could probably pull the motor out unit and replace it with a radio shack electric motor with the same voltages and amps. The ECU wouldn't be the wiser.

I would NOT RECOMMEND this if you're going to actually USE the omp, only if you're going to premix and the omp is not critical any more.

 

Being that I play with ham radio's (KC9EAW, in case you were wondering) I know radio shark like the back of my hand, and I play with resistors, just that I'm kinda lazy when it comes to this. I will see what I can make up for a clip-on resistor to replace the MOP and get rid of that zip-tied MOP that you speak of.

 

Wow, that would be awesome. Please let me know how you make out, I'd be greatful.

Thanks

 

S4 + premix = happy rx-7 owner

 

I bought an S5 NA with auto tranny that didn't work. I quickly swapped to a 5 spd tranny and as soon as i started to drive it, the thing was in limp mode. So i had a fried ECU and OMP. But i didn't know this. I replaced the ECU with a new one. The old OMP fried the new ECU. Then i replaced the OMP. The fried ECU fried my good OMP. Then i replaced both the OMP and the ECU at the same time, and presto, it worked like a charm!! So i have 2 fried ECUs, and 2 fried OMPs, just sitting around. If anyone can figure out a way to put a fuse or a resistor between the OMP and the ECU, that would be genius!!! Please let me know so that i don't have to buy any more OMPs and ECUs.

 

I had the same problem with my OMP frying my ECU. Between waiting for parts, buying a broken OMP, then buying a broken ECU, I've been without my car for 3 months now. Should be fixed today or tomorrow finally.

I messed around with this idea a little, but nothing too serious as I don't have the skills to design something. The problem is that the OMP has 4 different stages, so you'd need to have a resistor(s) that was RPM dependant to replicate these 4 different voltages. If anyone ever figures this out, please let me know. I would kill to get rid of this damn OMP, but I can't afford a standalone right now.

 

If you could, I would like to get my hands on one of them nifty little (evil) OMP's just so I don't have to pull mine and start ripping apart my daily driver. I would really like if i could advoid ripping everything apart until I have a working option.

 

You want one of my fried ones???
I could prolly work something out. How far from Harrisburg, PA are you?

 

Can anyone tell me if the s5 OMP needs to be actually mounted to the motor? I have my replacement one plugged into the harness and wire tied to the strut tower. Is there any reason that this might cause a problem? The malfunctioning one is still installed, and the oil lines are still hooked up to it. I just want to be sure that the new OMP doesn't need to actually be pumping fluid to be seen by the ECU as working.

 

I've never needed to remedy a bad OMP, but from previous posts, yes, they tie the omp away from the engine and premix.

 

Thanks. I've read that too, just wanted to see if there were any nay-sayers.

 

Update:
I bolted mine to the strut tower 2 weeks ago.
Started getting ECU code 27 (and others) about 1.5 weeks after.
As of tues, I'm getting code 27 along with limp mode
Remounted OMP and cleared ECU codes, but they came right back.... I may have joined the others in this thread.

Any luck with this?



P.S. I am tearing into the car, hardcore this weekend and possibly looking at resistor setups... I will update if I come up with anything

 

by the way, my original (related) thread is here:
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/s5-omp-removal-searchable-thread-326577/

 

I'm wondering, (hopefully Icemark or another Mazda-bot reads this) if you unbolt the MOP and leave it wired up while running pre-mix, would it still be a possibility that the MOP will burn up and still take out the ECU?

 

pre-mix sounds like a bitch to do every fill tho... im used to it on my bike but thats a little easier. how many ounces per gallon is it actually?

 

There is a guy here in York, Angel, I heard tell that he knows how to fake the ECU out that the OMP is still there on an S5..... If i get down that way, I'll see if I can get some ideas out of him.

 

Hurry!!!