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Old 07-11-2011, 12:31 AM   #1
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Default electrical problems on 2000 Miata

Hey guys I was having some problems with my battery light coming on so I changed my alternator and everything seemed good but today when I was driving my car I gassed it and it killed my electronics. So I drove it around a minute ago to try to see if it would do it again and it did. I can drive it at low RPM's and nothing everything acts perfect but if I rev it up past 3,500-4,000 rpm's my lights and radio would both turn off but if u let off everything would come back on. The new alternator makes a little wining noise I was wondering if I might have got a bad alternator but didn't think it could shut off my lights or radio because wouldn't the battery just take over? Does it sound like a short somewhere to yall?
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Old 07-11-2011, 12:34 AM   #2
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bad alternator
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Old 07-11-2011, 01:44 PM   #3
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Since voltage is regulated from the ECU on a 2000 I would think it's something other than the alternator. Have you checked the voltage to see what's going on? I've had a bad battery do some crazy stuff to my car before. If you have one you can rob from another car it might be worth a shot.
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Old 07-11-2011, 04:53 PM   #4
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19.8 volts at 4,000rpm that's way to high. I am about to go get a oem 2004 alternator that Tom at partsgroup has and try that. And I will pull the battery out of my 92 and see if that does anything also
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Old 07-11-2011, 04:58 PM   #5
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Originally Posted by MiataMX5 View Post
19.8 volts at 4,000rpm that's way to high.
?!

Yeah, that's a bit on the high side.


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I am about to go get a oem 2004 alternator that Tom at partsgroup has and try that.
I'm actually starting to agree with pdexta on this one.

If you're not aware of this, Mazda changed the design of the charging circuit beginning with the '99 model year. Prior to that, they used simple, internally-regulated alternators. From '99 onward, the regulation function was moved off into the ECU, where the ECU monitors system voltage and then adjusts the current being supplied to the field coil of the alternator.

It strikes me as somewhat unlikely that an alternator failure in an NB would be producing an output voltage that is too high. I'm not saying that it's impossible, it just seems rather suspicious.

If anything, I'd ask Tom if he has an ECU that you can borrow.


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And I will pull the battery out of my 92 and see if that does anything also
I don't think that removing the battery from one car will affect the charging system of another.
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Old 07-11-2011, 06:30 PM   #6
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just to add to joes try a spare ecu, if your car has an immobilizer you can not simply switch ecu's i ran into this issue trying to get my 01 motor running. you would require a reprogram or the matching immobilizer unit and key to the spare ecu. just trying to save you some time.

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Old 07-11-2011, 06:54 PM   #7
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He didn't have a extra one but I got the alternator. The alternator on the car right now I believe has something going on because of the noise it's making so I'm hoping that's what is causing the spike but will keep everyone updated after I install it. Also I am about to buy a megasquirt from braineack but rally want this straightened out before I install that one so I may try to source a ecu down if this don't work
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Old 07-11-2011, 11:36 PM   #8
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Put the 04 alternator on it and checked it at 4500 and it's 14.8-15 is that ok or still a little high?
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Old 07-11-2011, 11:59 PM   #9
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Check the ground on the throttle body
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Old 07-12-2011, 01:49 AM   #10
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Ok I will tomorrow. Is 14.8-15 still too high?
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Old 07-12-2011, 04:16 AM   #11
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yea thats still too high. 13.6-14.4 is a comfortable area.
Check all your grounds and make sure your battery isn't shot. If its not charging correctly, it throws a bunch of stuff out of wack. Don't forget that it seems your alternator crapped out due to something... start by checking ALL ground cables
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Old 07-12-2011, 10:12 AM   #12
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Ok I will swap another battery into it when I get off work and see if that drops it. Also does anyone know where all the grounds are? I checked the one where it grounds the battery in the trunk and the one on the ppf frame buys that's all I could think of. Also the one on the ppf frame was loose prior to me putting either of these two alternators on. I figured that was what burnt up my first one
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Old 07-12-2011, 01:16 PM   #13
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Did you try the one right by the TB like I said?
Im sure its not the only one but I had a problem on my 99 where it was overcharging at 17-18 volts and would cut out when reved high, turned out to be that ground was loose/dirty.
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Old 07-12-2011, 01:55 PM   #14
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Ok I will tomorrow. Is 14.8-15 still too high?
I'm working with a new alternator and new battery in the last 2 months and my Scangauge will still make occasional trips to 14.8-15 when I unload something in the electrical system (turn headlights/AC off, etc) or right after starting when the system is trying to bump the battery back up. On average, I see 14.3-14.7 depending. It's not uncommon for your electrical system to charge at 14.XX so I wouldn't worry about it too much at the moment. Does it drop down after driving around a bit?

+10 on check your grounds. Listen to full_tilt, he speaks truth. I ended up spending a couple hours with my dremel disconnecting and polishing all the electrical contacts, mating surfaces and the associated bolts and coating with a very thin layer of dielectric grease before reassembly. Call me crazy but the car runs far more smooth now. Well worth the time. Give it a shot, it can't hurt.
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Old 07-12-2011, 06:13 PM   #15
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Haven't had a chance to check the ground on the tb yet but when I get off work I will. Also I checked the output right after I cranked it. I might drive it around for a min today and check to see if it drops.
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