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Old 10-19-2014, 05:38 PM   #1
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Default nb alternator isn't charging

Hi everyone, my 99 is acting up yet again. So here's the history:

Replaced the alternator twice, found the lead wire coming off the alt was corroded and it broke. Replaced that wire with one from an 01 harness (just the wire by cutting the lead on the old one and attaching the new one to the fuse box and alt). No problems for a bit. Then about a month ago, I change my oil and wrestle with the oil filter because Mazda changed the oil filter size. Turn the car on, charging light is on. Replaced the battery and alt. Also swapped ecu's. No luck. So it's obviously wiring. Also, i found one of the under dash relays had burnt wiring. Wired in a new connector and replaced the relay. All the fuses under dash are good. How do I trace this down besides put a volt meter to the lead wire? The lead wire is giving battery levels so the alternator isn't charging. How do I diagnose to see if the other 2 wires are working? And what's the easiest way to trick the alternator into charging? Put those two wires to ground/my nips?
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Old 10-19-2014, 06:19 PM   #2
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Easiest way to test the Alt, move it to a known working Miata.

No simple way to fool the Alt to charge, it's PWM controlled. You will burn the controller by messing with it manually.
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Old 10-19-2014, 08:31 PM   #3
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At one time, it was possible to take an alternator into a shop such as NAPA or CarQuest, and they would put it it a test bench that drove it with a belt and tested it under load. I honestly don't know if they've since updated the test benches to work with modern ECU-controlled alternators or if they can still only test the old one-wire stuff, but it merits a phone call.

It's also possible that a Mazda dealer might be equipped to do this test.

If you have access to an oscilloscope, you can probe the control wire and see if it's being driven. This isn't something you'll be able to see with a voltmeter.
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Old 10-19-2014, 11:09 PM   #4
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I've swapped 3 alternators. I don't know if all are bad, but I think (at least I'd hope) the odds are very unlikely that all are bad. Any ideas on what else to check? I'm 90% sure it's a broken wire or something along those lines given the car's history plus the fact it crapped the bed after I wrestled with the oil filter. The engine to body ground is so corroded that I'm afraid the bolt will snap if I loosen it. That aside, I'm clueless as to what to look at next.
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Old 10-20-2014, 07:31 AM   #5
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Quote:
Originally Posted by thegrapist View Post
Any ideas on what else to check?
(...)
The engine to body ground is so corroded that I'm afraid the bolt will snap if I loosen it.
Nothing comes to mind.



You know that you have a good battery connection and a poor ground. After you fix the ground, the only things you won't know are whether the control signal is getting to the alternator and whether the IAT (intake air temp) signal is getting to the ECU. Testing the former requires an oscilloscope. The latter can be looked at with a voltmeter at the point where it enters the ECU. I'm sitting on the crapper at the airport right now and therefore don't have the calibration table in front of me, but you should see some stable voltage between 1-4 there.

Why does the IAT signal affect the alternator? Because spacecat.
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Old 10-20-2014, 08:40 AM   #6
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Thanks. I swapped the IAT with a known good one yesterday. Forgot to mention that.

But I'll check those and hopefully can fix that ground.

P.S. I'm also pooping. We're poop pals
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Old 10-20-2014, 10:39 AM   #7
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Measuring the Alt control from the ECU connector to the Alt connector would work.
1O and 1T are the ones that goes to the alt connector
1O Grey/Red
1T Grey

Adding an new extra ground strap is not a bad idea. Solved many issues for me.


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Old 10-20-2014, 03:32 PM   #8
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Oh, you're the coolest. Thanks

Which ground strap are you specifically talking about?
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Old 10-20-2014, 05:35 PM   #9
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Quote:
Originally Posted by thegrapist View Post
Which ground strap are you specifically talking about?
I have an extra one from a tranny bolt to the frame rail, generic strap, from any parts store.
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Old 10-20-2014, 07:06 PM   #10
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Awesome. Thank you so much. I'm replacing the connector to the alternator that has two wires, going to replace the three major grounds, and add another.

If that doesn't work I'm going to run down the wires. If that doesn't work I'm going to fill the tank, leave a flare sticking out of the filler neck, and push it off a cliff.

Last edited by thegrapist; 10-20-2014 at 07:16 PM. Reason: me grammar good
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Old 10-26-2014, 12:32 PM   #11
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Fixed it.

Installed a new ground wire coming from the motor. Nothing

Pulled off the ground wire on the ppf and cleaned it up (chunks of salt, 1/8" thick came off. whoops). It's going to break soon, so I'm in the market for a new harness. Still nothing.

Pulled off the two wire connector for the alternator and went on a bit too easily. I bent the pins so it'd would make a tighter connection with the pins on the alternator.
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Old 10-27-2014, 10:29 AM   #12
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Out of curiosity, how much of a pain in the ***** is it to replace the whole charge/battery harness? Is it just pulling up carpet and feeding? Or do I need to pull the dash again?
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Old 01-13-2015, 11:56 AM   #13
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Did you ever figure out the issues with your alternator? I'm having the same problem with my NB and had the alternator completely rebuild and it still won't charge.

-B
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