hornbm

I am in the process of swaping a 89 N/A engine into my first gen.

Because I have to use the 12a front cover, I cannot mount the electric OMP that the 89 motor uses.

Also I do not want to run premix. At least not yet.

So I have heard that if the ecu does not detect the electric OMP it will go into "limp mode" and will barely get above 3000 rpm.

How do I trick the Stock 89 ECU into letting me use a mechanical OMP?

No7Yet

Leave the MOP attached to the harness as a unit, and tie it out of the way. Block off the front cover location and run premix or an S4 mechanical unit. That's really the only way.

Brandon

hornbm

does anybody know if this will work if I use the 12a OMP?

It seems odd that letting the 89 OMP just hang there would work, but it kinda makes sense too.

this will for sure, prevent the LIMP mode from turning on?




I guess this would be a simmilar setup as trying to run an s4 OMP on an S5 engine by using the S4 front cover. Hasn't this been done before?

I did a search but I didnt find anything about the "limp mode" occuring when the electrical pump is not attached or working right.

No7Yet

If you're using the S5 ECU, you MUST use the S5 OMP. The ECU has a number of inputs and outputs relating to the OMP. It can detect if it's there, as well as if it's following it's "directions" correctly. If you absolutely don't want to use it, then yes, you have to just disconnect it from the engine as a unit and tuck it away somewhere, leaving it connected to the ECU.

Why must you use a mechanical OMP? If you're going to go to all that trouble, just block it off and go premix.

Brandon

nosajwrx-7

Is the ECU just looking for a continued circuit? Could you just make a jumper wire, and trick it into thinking the OMP is there? I don't know, never done it, I am just wondering out loud!

No7Yet

No, the OMP is a stepper motor, which also turns a small potentiometer in addition to the oil feed pump.

Brandon

nosajwrx-7

But, my question is what is the ECU looking for from the OMP. I understand that it tells the OMP to operate, but what kind of signal does it send back, other than a continued circuit. The reason I question this is because if you just leave it there to hang, what kind of signal is it sending back.

No7Yet

Uh, read my last post. I just answered that.

Brandon

nosajwrx-7

What is a potentiometer?

No7Yet

A potentiometer is (basically) a variable resistor.

To break it down for you, the ECU looks for continuity in the MOP circuit. When it "sends" commands, it "sends" them to a stepper motor. This motor adjusts a pot, which "sends" back a resistance value to the ECU - if the two don't correspond, the ECU throws an error and goes into limp mode.

Before you ask, yes, you could defeat it, but it would not at all be worth the trouble. You'd have to keep track of three state variables and interpret the stepper signals from the ECU. If you're going to that sort of trouble, you might as well just redesign the OMP.

Brandon

nosajwrx-7

Thank you very much for the information.

hornbm

I should probably clear up why I dont want to use the 89 OMP.

Because I am swaping into a 1st gen, I have to use a 12a front cover because of the front mountings.

The 89 OMP will not bolt up to the 12a OMP spot.... so thats why I cant use the 89 OMP.

now wouldnt the disconnected 89OMP be sending some kind of signal to the ecu... like I dont have any oil, or i'm disconnected, and then throw it into limp mode?

cymfc3s

yes it would. To get by this you can take an 89+ OMP and plug it into the harness and tuck it away by the charcoal canister.

hornbm

lol.... I meant it not being connected to the engine, it would have been connected to the harness... obviously!


However some good news. When I bought most of my 89 parts, the guy included a 12a front cover that was "modified for this purpose" I didnt exactly know what he did, but I just went out and looked at it and he made it so the 89 OMP will work on the 12a front cover!

This is going to be so much easier!