Miata new CAS still doesn't run

That's a shame. It's going to be a simple fix, you just haven't found it yet. You cannot diagnose anything with a code reader, you need something with data. If you had that, you could see if you are getting an RPM signal with the engine cranking. No RPM signal means you either got a bad sensor or something isn't turning or you have a cut/broken wire.

Either ay if you see 9v where you should see 12v, you can't go any further until you have 12v again. Period. To try otherwise is just a futile waste of time.

I reiterate that if the compuer doesn't see the engine turning, it won't fire the plugs. So of course you won't have spark.

Someone at the junkyard is going to love you if you throw this car away.

Pull the main relay and inspect the terminals. If you're truly only seeing 9v at the white/red wire, then I'll bet you've got corrosion on those terminals. And yes, most computers have a minimum voltage before they wake up.

In reply to carguy123:

I'll give you $50 over their offer. Can pick up in two weeks.

We're not really throwing the car away, although we felt like it, and once again, the 9 volts is only because we've cranked the battery down AGAIN. It is not the cause of anything.

But we are taking it to a shop.

We know it has to be something super simple and that's what is so frustrating. We are going to find it's a broken wire, bad connection, blown fuse, something just that simple.

Cool. But what they're saying above is don't troubleshoot with low battery voltage because it'll give you false readings and lead you in the wrong direction.

carguy123 wrote: We know it has to be something super simple and that's what is so frustrating. We are going to find it's a broken wire, bad connection, blown fuse, something just that simple.

The first step in finding almost any electrical issue is to not to it with a drained battery. You seem to be determined making this way harder on yourself. Why have a known issue in the loop that you can easily fix? It doesn't matter much that you know why it's low. You still know it's low.

Low has nothing to do with it at this point. It had the same issue when it was high.

Low is a temporary state that happened several times since the engine wouldn't run and any cranking gradually drained the battery. Same problem and same symptoms regardless of the temporary state of the battery.

Can I give you an example? Keith pointed out that the ECU might not power up at 9 volts which would lead to it not turning on the fuel pump. Not the reason your Miata stopped running but if you're troubleshooting with low voltages it could lead you down the wrong path. But good luck. Hope you guys get it running and back out autocrossing soon. Sounds like a multigenerational family event.

Guys, it sounds to me like he's saying he charged it back up and it didn't fix the problem. Move on. :)

Can you borrow an oscilloscope or logic analyzer? That's really the right tool for debugging this.

You're right Codrus, the issue was the same with a fully charged battery and when we would run the battery temporarily low before recharging it again.

PROBLEM RESOLVED!!!

And it was simple (once we found it). But it wasn't simple to get it to the shop to have it found.

I'd sold my car hauler so we had to somehow put the car up on a 16' landscapers trailer with a broken ramp. You can do that if you get creative with wood, steel, aluminum and fortitude.

My wife was steering with my son & I pushing. A Miata is light, for a car, but heavy for a push up a wonky ramp while being careful not to scrape the sides on the trailer.

Tying it down so it would travel 1.5 hours was another experience, but we finally did it.

When we got it to Track Dog in Garland he was as puzzled as us. He threw new coil packs on it just to be sure that both coil packs hadn't gone out due to some weird coincidence or some kind of short and still no spark. He went through every thing we'd done and why we'd done it and said what we'd done ought to fix it so he said let's replace the Crank Angle sensor with a known good one and start from the beginning all over again.

When he pulled the old new one off I'd just put on he said "Here's the problem you set it too tight and scored a deep gully across the surface." I told him that it came with a slot on top and I just thought it was designed that way and was a different or improved model.

We put the new CAS on it and it fired right up!

It seems that Autozone gave me a CAS that someone else had installed, messed up and returned. When you looked at it closely you could see the new & improved slot across the top didn't have square edges and clearly was due to the sensor being installed too tight before. My wife & I had looked at this before installation and even searched the interwebz for info on whether the gap should be measured from the bottom of the slot or from the top prior to ever installing it so we know it was there before installation. The tightest I had ever set it was .029.

In the process we discovered one short trigger tab on the wheel which is what had been giving the intermittent signal that we'd gotten a code for too. I just thought the old CAS had been installed with too big of a gap and at speed it just wasn't reading it 100% of the time.

So days and hours of our lives, not counting all the extra money and back breaking labor to load the car on the trailer and the long drive plus the cost of the shop was due to lax policies or an incompetent counter person at Autozone.

BTW Track Dog had a really cool 300 hp red Miata with carbon fiber hood and great looking yellow supercharged Track Dog track car with about 300 hp also that we looked over. That means the trip wasn't for nothing, but I'd have rather gone just to look at the cars.

Cool deal.