I'm considering swapping out the heavy (18#) and heavy duty (80amp) alternator on my 2004 miata track day car for a lightweight alt.

The problem that am considering, is that the OEM alternator uses a phase/driver circuit (in which half of the regulator resides in, and is controlled by the ecu).

I would like to swap in a self regulated "one wire" alt and merely unplug the ecu connectors; but am unclear if this would merely send a code, or if the car might not run.

Has anyone tried this?

 

Tons of NBs have done this. There's a few dozen threads on the subject here.

https://www.google.com/?gws_rd=ssl#q...miataturbo.net

 

Thank you. I was able to get a decent diagram from a couple of the threads.

However, I'm still wondering what will happen if the ECU alt leads are left unplugged?

In reviewing the search, I haven't seen anyone swap a self regulated alt for a P/D alt and still retain the OEM ECU.

 

unplug your current alternator and find out.

 

It sounds like the easy/obvious test!

 

Why bother keeping the stock ecu? The 8-10lbs you save from the alternator is kind of a drop in the bucket compared to the like 10hp you get from a standalone.

 

Are you telling me there are 10hp simply to be gained from a better tune on a stock car? or is my sarcasm meter broken?

 

No, that's what he's telling you.

 

Depends on the year miata, but yes it is possible with removal of the MAF/AFM.

 

Good plug for the Megasquirt.

I did just replace the PD alternator with a standard lightweight. I used a small NDIF/nippendenso internal fan and set it up with a standard regulator... set it to 14.7 V. It charges great, but does cause a dash charge indicator light to light up. With the ck engine, airbag, batt and the occasional the abs lighting up the dash kinda looks like a Christmas tree.

 

then you didnt mod the wiring properly.

 

Yeah, I'll mod it by pulling the bulbs..

...Unless, of course, you are being serious?

It looks like the charge indicator light (brn/red) comes off the ecu, and I believe that this is fed by the phase/driver circuit (gry, gry/red). I suppose that I could try to hook up a method to simulate the signals that the P-D portion of the circuit would normally see, rather than just unplugging the connector as I have done. Also, I need to mention that the only new light is the ck batt light. The others have been on because of previous lapses in judgement (gutting airbags, re-chipped ecu and poor braking skills)

For the moment: Leaving for the track tonight... and the car charges/runs!

 

The alternator worked perfectly over the event this weekend.

 

or just do this:



i.e., mod the wiring correctly.

 

yeah, that looks good!