Been dealing with this intermittently for the past couple of years and haven't been able to resolve it.

What I have:

2002 NB2 w/ a non-VVT motor and a decent turbo setup using MS3 Pro PNP for management.


Here's the deal:

When I drive for an 'extended' amount of time, usually going out to do some shopping, about 50% of the time, either after my first stop or my second stop, I'll start up my car and the alternator will not charge. I'll be running on battery only. I usually only notice a few seconds after getting out of the parking lot and down the next street, then have to find an emergency place to pull in while revving the car to keep it from dying. I end up having to sit there between 10 and 30 minutes. After 10 to 30 minutes, when I attempt to start up the car again (assuming I still have power), the car starts, everything seems normal. Sometimes this takes multiple start up attempts during that 10 to 30 minute window.

I have:

1. Replaced the battery
2. Replaced the alternator 2x (using old OEM at the moment)
3. Replaced the belt
4. Checked belt tension
5. Checked the nut/wire tightness, seems fine
6. Updated the alternator control on my MS3 to delay ramp
7. There is no noise when this happens that is odd
8. This last time (today) there was a very slight electrical burning smell, but it was just barely.

Obviously none of these things has fixed the problem. The clear issue with troubleshooting this is that it only happens when hot. I've tried to make it happen driving around my garage and then parking and can never make it happen, so it always happens 5 to 10 miles away from anything that can help. I've talked to my friendly ai bot endlessly about this and gotten nowhere. Any advice would be great.

I can post a log and tune if anyone thinks that is helpful, but this seems unrelated to ECU stuff to me.

 

model year?

 

Sorry! NB2, 2002.

 

I have no idea if this is related, but I had similar problems with my starter from bad main grounds. I diagnosed by grounding the block and/or battery to the frame with a jumper cable.

 

Are there any other grounds besides the one by the dip stick? I can check but that's the only one I'm familiar with.

 

I don't know the Miata, I had this problem on another vehicle. The cars I have worked on have two main grounds, one between the engine and frame, and battery and frame.

 

Yes.
There is one that goes from the battery to the PPF or diff, can't remember which off hand. IIRC it is too small, I think I used a chunk of my old positive cable to replace that ground. Maybe one to the chassis in the trunk too, I would need to look to be sure, maybe I added that one later. But yes, all my other grounds make that flimsy shunt by the dipstick look like nothing.

 

Oh i defintiely have that one. Any other recommendations for ground locations?

For what its worth I got the car in the air and inspected everything again from the wiring etc and all looks normal.

 

How is everything now?

 

Issue went away until it happens next time. I've looked and found nothing and really done nothing.