Voltage Issues (1997 NA Miata)

[zachhouseknecht]

First off hello to everyone here, I hate my first post being about a problem, but I guess that's just how it is. So here's the deal. 1997 Miata NA with 233k miles. I have had it over the past 4k or maybe a little bit more...with no issues, just a few small things. But this thing is something that is stumping me currently.

So here's what's going on, I'll drive the Miata 15 - 30 minutes, maybe a little longer, park it, and try to start it within 5 - 10 minutes. Usually no dice....it seems to be fine one day and no start the next. That being said, let the car sit for a day, or until the next day, and it usually turns right over. I've pretty much gone through checking all the usual stuff - spark plugs, clutch safety switch, and I've wiggled the ignition cylinder around, it seems to be secure and not cause any issues with starting... I have been running Torque and OBDII Bluetooth adapter over the past couple drives to help diagnose this issue. Ignition in and starting usually gives me about 13.6 - 13.7 volts, then driving around it will vary in between 13 and 13.5, I don't see anything wrong with that. But some drives, it will drop to 12 - 12.5 and never come back up while driving. Shutting it off yields two different results as well, the days when its around 13 or more while driving, it usually drops to 12 upon shut-off, but the days where its at 12 or a little more it will drop off to 6/6.5. I've replaced the battery, even when it reading healthy, in hopes it would resolve the issue, but of course, I don't think the issue is the battery (or the terminals).

I've done some Googling, and of course most posts point to alternator/belt. I've haven't had the chance to bench test the alternator, but the belt it self seems fine (squeaky on some wet days).

If there's anything else I can check, or any other people that have had a similar problem/solution, I'd love the help/expertise. Thank you!

[RustRat]

When it doesn't start, does it even crank, or is it dead? At first I thought it was the coil pack, as a friend of mine had similar problems, but he had a constant 14-16V supply, never dropped below that. Maybe it's worth checking it, as well as the wiring to and from the coil pack, and also their pins.

Then, just check the alternator, it might be dead.

[zachhouseknecht]

When it drops off to 6/6.5 it tries to crank, but its super slow and maybe only gets 1 or 2 cranks. No start. But "regularly" with 12 - 13 it cranks slow maybe 2 - 3 times then springs to life.

I can check the coil pack, I'll also probably be testing the alternator too anyways, haha.

[zachhouseknecht]

Alright, well I went to start the Miata today, so I'm bumping this thread in hopes somebody will know what this is. I'm assuming alternator/grounding unless somebody says otherwise.

So hop in, turn key, nothing. All I get were the regular dash lights - including "Charge" this time. I go to turn the key fully and nothing. No crank, "no change in power." I use quotes there because it does fluctuate about .5 volts. But the battery is above 14. Tried to boost/jump (even though it "had enough power" - because this has worked in the past), but nothing....

Hopefully I can get it over to my work (we have a shop) to check the alternator, since I'm pretty sure it's done....

[— kung fu jesus —]

So signs point to an alternator from your first post almost 3 weeks ago and you haven't tested it yet? Nor the coils?

If you turn the key and you register no change in power, that would indicate a bad ignition switch to me, or the starter.

[zachhouseknecht]

Didn't have the chance to get to it yet, when I asked. Car is not my dd, and I have to get it started to get it in to the shop at work.

Got it in to the shop today. Rewired the ground at the battery, since it wasn't great, went over all the fuses, checked over power at the alternator and the battery. Narrowed it down to the starter, since it didn't start when I tried to left. Hit it lightly and boom, fired right up. This after ruling out the ignition switch, and the fact that the starter was getting power, just not doing its job.

Thanks for the help, on to replacing the starter!

[NCGreasemonkey]

Sorry I missed you're earlier posts.

Hope the starter was all it is. But...

1) Be careful how hard you tap-test newer or Japanese starters. A good-ole American whack to these tighter wound one's can seal their fate.

2) You mentioned using a scanner. If the readiness doesn't reset to unready on OBDII then your voltage readings might be off.

3) Check the A/C ripple of the alternator, also. That can look like good voltage, sometimes, in a DC test and cause havoc in the memory for the fuel trims, learned idle and base-line running.

[— kung fu jesus —]

I wouldn't rule out the ignition switch 100% yet. The intermittent issue leaves me suspicious the contact or structure may be an issue. Proceed to the next tests.

[marathonboats]

I agree with 1) Be careful how hard you tap-test newer or Japanese starters. A good-ole American whack to these tighter wound one's can seal their fate.