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Old 06-03-2013, 01:51 AM   #1
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Default Voltage drop makes my engine chew up the alternator belt

From time to time the voltage of my car drops and causes the alternator belt to squeal, smoke, and eventually self-destructs. I took a log of it today and the voltage hangs at around 11volts for some time then it picks up to the regular 13-14v. During this time the belt squeal and smokes.

I am wondering what could cause this drop. Alternator malfunctioning? is my battery too small? I replaced the stock alternator with a Duralast unit less than a year ago. However, my battery is the recommended Duralast replacement for a stock miata which seems very small in my opinion. Of note, my light faints when the brake is pressed or when the turning signal or hazards are turned on even when the belt is not squealing.

msq and log are attached the drop starts at around 137s
Attached Files
File Type: msl 2013-06-02_23.36.49.msl (1.88 MB, 105 views)
File Type: msq 2013-06-02_23.55.26.msq (39.8 KB, 73 views)
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Old 06-03-2013, 02:19 PM   #2
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Sounds like the alternator is locking up.
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Old 06-03-2013, 02:22 PM   #3
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Yeah, this strikes me as a mechanical problem.

With the belt removed (and the engine off) does the alternator spin freely when turned by hand? You should be able to twirl it and watch it coast down smoothly.
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Old 06-03-2013, 02:27 PM   #4
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The horror stories i could tell about Autozone alternators...

I swapped alternators 4 times in one day on my daily driver this past fall.
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Old 06-03-2013, 02:28 PM   #5
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The horror stories i could tell about Autozone alternators...

I swapped alternators 4 times in one day on my daily driver this past fall.
Slow learner?
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Old 06-03-2013, 02:29 PM   #6
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Heh, lifetime warranty means you'll be replacing it for the rest of your lifetime..
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Old 06-03-2013, 02:32 PM   #7
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Slow learner?
Well, only two were Autozones... (first two), at which point i angrily told them to take their piece of **** alternator(s) back.

Then swapped in an OEM one from another car just to make sure i didn't get angry at Autozone for no reason. (So that involved removing one from that car, then re-installing once it was found that that alternator DID work on my DD.)

Then ended up with a lifetime reman from Advance. (Verified they were being built by a different company than Autozone.)

Shitty day. I can now swap an alternator in 10 minutes on that car, though.
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Old 06-05-2013, 03:45 PM   #8
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I haven't inspected the alternator yet since I'm in the middle of moving and I had the exhaust was being installed in the car. However, something curious is happening now. The meter fuse has blown 3 times since I made this post and I have barely driven it.
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Old 06-08-2013, 03:11 PM   #9
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I haven't inspected the alternator yet since I'm in the middle of moving and I had the exhaust was being installed in the car. However, something curious is happening now. The meter fuse has blown 3 times since I made this post and I have barely driven it.
Sounds like you have a short, of course... I would start by looking at the alternator and main wiring harnesses on the passenger side of the engine, going back to the rear of the car. Not sure which fuse you are referring to, but that will tell you which circuit to look at.

Definitely time for a new alternator in any case.
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Old 06-09-2013, 08:29 AM   #10
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Voltage dropping has nothing to do with the belts getting chewed up, it's an alignment issue or the alternator is not spinning freely. the voltage drop is an effect of...
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Old 06-09-2013, 09:19 AM   #11
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Bad bearing in the alternator. It allows the armature to **** sideways (heh, heh. He said ****) and short out. Also, bad bearing accounts for locking up and smoking/shredding belts.
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Old 06-09-2013, 10:06 AM   #12
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This same thing happened to me recently at a track day!
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Old 06-10-2013, 12:37 AM   #13
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Sounds like you have a short, of course... I would start by looking at the alternator and main wiring harnesses on the passenger side of the engine, going back to the rear of the car. Not sure which fuse you are referring to, but that will tell you which circuit to look at.

Definitely time for a new alternator in any case.
Meter fuse (15a) = no dash/tach. Also, battery depletes when this happens.

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Voltage dropping has nothing to do with the belts getting chewed up, it's an alignment issue or the alternator is not spinning freely. the voltage drop is an effect of...
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Bad bearing in the alternator. It allows the armature to **** sideways (heh, heh. He said ****) and short out. Also, bad bearing accounts for locking up and smoking/shredding belts.
****

I'm going to go replace the alternator and the battery, also get a new belt while I'm the shop. What's a good method to correctly tighten the belt? The manual mentions to check by means of the deflection of the belt by being pressed, but I'd like something less vague.
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Old 06-10-2013, 06:45 AM   #14
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As tight as you can hold it with one hand while you tighten the bolt!

Really, it's not that critical. You just need it tight enough that the belt won't slip.
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Old 06-10-2013, 07:32 AM   #15
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Along it's longest run, you shouldn't be able to twist the belt more than 45 degrees.

Or pluck it, should be a B flat IIRC.
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Old 06-11-2013, 06:28 PM   #16
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Along it's longest run, you shouldn't be able to twist the belt more than 45 degrees.

Or pluck it, should be a B flat IIRC.
Thats interesting. I have a tuner so I'll see if I can get B flat lol

Also, chasing the short radio and mid-console are out. I rattled the wiring and tried to find any loose cables and nothing. All info about this short talks about the transmission tunnel. I recently added some insulation in the cabin but messed with nothing related to electronics o_O
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Old 06-11-2013, 07:08 PM   #17
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Originally Posted by rleete View Post
As tight as you can hold it with one hand while you tighten the bolt!

Really, it's not that critical. You just need it tight enough that the belt won't slip.
No way. Its super critical. You want it just tight enough that it squeaks for half a second on startup. That way you know its at the minimal tightness to not slip so you have less parasitic drag for that 0.05 extra HP to the wheels.
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Old 06-18-2013, 12:55 PM   #18
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Thanks, richyvrlimited. The belt was loose when I thought it was tight enough. I could twist it about 90* with no effort. I tighten it so that it twists about 45* or so and I haven't had any squealing. However I do get a faint in the dash when turn on accessories or when I step on the brake light but it quickly goes away. I'm sure this has to do more with tuning the idle than anything else.

As for the short, there were two cables around the transmission that sparked when they came in contact with the transmission housing. I covered them with electrical tape and the issue disappeared. For now the car run well, I just went back to Orlando from Miami without any issues. Thanks to all for the help
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Old 06-18-2013, 01:07 PM   #19
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So you dont have reverse lights?
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Old 06-18-2013, 07:32 PM   #20
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I do... I don't know what those other two wire are for.
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