Going Down To Electric Avenue - NB1 Starting Headaches
 

Well, after years of janky starting I'm forced to "do something" to fix it.

Previous symptom; intermittent multiple key-on, key-off cycles to achieve engagement of starter. Attributed to a 20+ year-old starter - replaced. Result: no significant difference in starting performance. FAIL.

Newer symptom; initial low cranking RPM (even with a fully charged battery - 13.1V at the terminals), followed by sudden unexplained faster cranking RPM and successful start.

"Final straw"; on a recent trip to Lowe's Racing Supply after a 20-min shopping trip car fails to start. Battery shows 12.6V prior to start but drops as low as 10V when the starter solenoid engages (but the starter wouldn't spin). Attempts to jump the car were fruitless and a new (Advance Auto) battery purchased and installed. Following that, the solenoid would engage, the starter would turn VERY slowly (approx 80RPM) and the voltage would drop as low as 8.6V. Eventually (with the help of a jump) the starter spun fast enough a start the engine.

With the new battery on a trickle-charger overnight, the car reverted to the "Newer symptom" scenario, at which point I decided to re-wire the whole damned thing and start from scratch (pun intended). My assumption is that there is either an intermittent short somewhere in the primary starting circuit, or some other fault in the power or ground side of that circuit. I've already installed a brand new, shiny ground strap for the engine, and made sure that the primary ground for the battery are contacting bare metal on the chassis. My next "adventure" is to rip out the primary wiring from the battery to the starter (and, if necessary, the alternator primary wire too) and replace it with brand new cables and lugs. I also had a problem 15 years ago with a faulty ground from the main fuse block in the engine bay, so I intend to replace that as well.

One note here before I embark on this journey is that I am a Mechanical Engineer by training, therefore I have a love/hate relationship (mostly hate) with electricity. So I'm sure that there will be massive failures and much cursing involved. Hopefully, the end result will be a perfectly functional starting and charging systems and I will no longer be a in fear of being stranded any more.

I’ve had something similar happen on a non-Miata. It was the key switch itself. The contacts were dirty / burnt. Not sure where in ATL you are, but I have a key switch you are welcome to. Only issue is I only have 1 key and need it for the trunk, so you would need to change out the lock barrel to your key or have a key made for it (You can borrow my key to do that). FYI…I’m 1 mile from RSpeed.

Thanks for the offer (I'm in Alpharetta), but I've long since replaced the key switch with a pushbutton that feeds a relay which in turn feeds the starter circuit. And the key-on/key-off problem predated that change, so I'm confident that isn't the source of the issue.

I appreciate any and all other theories.

I'm not familiar with our grounds but is the grounding that goes to the PPF still there and in good condition? I heard missing that could cause issues.

Last time I was under the car it was. I'll have it on a hoist tomorrow and will verify that.

LOL...Definitely not the key switch then!

I'm closer to a sanitation engineer than an electrical engineer, but it really sounds like you have some contact corroded / not touching & arcing to me. Initially it arcs and gives you a weak electrical flow, as it keeps arcing it heats up the metal and the leads then touch and you get good electrical flow.

To test if it's the "Main" wire or ground...Use some jumper cables and bypass the cars wiring, testing each "side" one at a time...That should help you figure out if it's the positive or neg side and what wires to spend your time looking further into.

Good Luck!

Thanks.
I'll be doing the "jumper cable thing" as my first pass. I just hope I don't electrocute myself doing it. :facepalm:

Okay, so I spent most of the day on Saturday checking and testing the starting and charging circuits on the car, reading through wiring diagrams and trying to get "inside the head" of my nemesis - electricity. All with little, or no effect. I check and cleaned all of the grounds (including the PPF), re-wired much of the starting circuit with "real" copper power and ground cables. I even put in a overall system power-cut so that I can just shut down everything (I have a lingering parasitic drain that I haven't devoted the effort to eliminate). Bottom line, on Saturday evening I was no better off than I was before.

That night it occurred to me that the only thing that I hadn't checked was the relay circuit for the push-button start that I have in place. So, Sunday I went out and took a look at that wiring. What I saw was surprising (even for me and my non-electrical tendencies). There were some horrible examples of "attempted soldering" and I could even see that the power-carrying wires were starting to corrode because of those botched solder joints. So, I whipped out my wire-cutters and excised the offending joints. Then I pulled out some yellow self-sealing butt connectors and crimped the trimmed and fresh new wires together with a "real" crimping tool. Here's the plagiarized diagram that I used originally.
https://cimg1.ibsrv.net/gimg/www.mia...bdf590da4b.png

Then came the moment of truth...I turned the key and pressed the start button, and...it started without drama!

But, before I claim a full victory, I'm letting the car sit without aid of a battery charger for 24 hours. If it starts without hesitation, then I will declare victory.

Stay tuned...