Voltage Drop with A/C (Now voltage spike while driving) - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 04-26-2011, 12:04 PM   #21
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Quote:
Originally Posted by Joe Perez View Post
Are we quite certain that falling voltage is causing RPMs to fall, and not the other way around?

At first glance, it seems to me that effect and cause are being mistaken for one another.
I'm with Joe on this... Those little alternators don't have a lot of nuts to begin with, add a little wear and a lot of load at a sub-optimal speed for them (most alternators don't get to full output till 1800rpm or so)... You're just asking it to do more than it can do. I hope you're running a full size battery?
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Old 04-26-2011, 12:14 PM   #22
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I wasnt trying to suggest that the low voltage was causing low rpms but that somewhat low rpm dips are causing incredibly low voltages when the a/c is running.

The voltages maintain 13.5v in most conditions without it running.

I have the run-of-the-mill "high performance" oem battery.

the voltage spike today is what really had me headscratching. I couldn't get my car running without holding the throttle, and it wouldn't drive. The voltages never came back down so I shut the car back off...took a couple of key cycles before it finally reported 12v again and all was normal.
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Old 04-26-2011, 12:20 PM   #23
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High voltage spikes are definitely the regulator shitting itself... Just no way around that. Time to try a different alt.
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Old 04-26-2011, 01:00 PM   #24
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ughhh... they are so expensive.
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Old 04-26-2011, 01:10 PM   #25
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Not as expensive as a fried harness.
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Old 04-26-2011, 01:14 PM   #26
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Quote:
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ughhh... they are so expensive.
$40 from Panic Motorsports. Just think of it as the money you could have spent seeing Bad Religion.
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Old 04-26-2011, 01:37 PM   #27
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why pay $40 when you can pay $145
http://cgi.ebay.com/ebaymotors/1992-...#ht_2245wt_939
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Old 04-26-2011, 01:42 PM   #28
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i head those arent even that great. are they PNP?

the stock is 60 amps. I was looking at some 65 amp ones... do i really need 140Amps?

I was thinking about going with a remanu. instead of used.


what are they rated at 12 or 14v?

12 * 60 = 720watts
12 * 65 = 780watts
12 * 140 = 1680watts

I do have a 500watt amp in the trunk...but I doubt I need that much reserve.

assuming 14v running

14 * 60 = 840watts
14 * 65 = 910watts
14 * 140 = 1960watts


this however could work out: http://cgi.ebay.com/ebaymotors/MAZDA...item45df0e5fc3

Last edited by Braineack; 04-26-2011 at 02:06 PM.
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Old 04-26-2011, 02:20 PM   #29
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NAPA or Mazda
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Old 04-26-2011, 02:31 PM   #30
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does the 94 alternator swap over if I change the pulley? those run at 70A.
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Old 04-26-2011, 02:55 PM   #31
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Quote:
Originally Posted by Braineack View Post
does the 94 alternator swap over if I change the pulley? those run at 70A.
My understanding: they are otherwise identical. If you can get your hands on one, see if the connectors are similar.

Getting the pulley off is a PITA. I've pulled them two ways. The dumb way is to hold the pulley in a vice - 100% chance of damage to the pulley. The recommended way is to pull the case apart and hold the rotor in the vice.
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Old 04-26-2011, 02:59 PM   #32
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they are identical but for the pulley. Problem would be removing the ribbed one and finding out my v-notch's keyway doesn't fit.

I'll probably pick up a remanufactered 1.6L automatic alt, they run at 65A vs the 60A of the manual.

ill just leave the a/c off in the time being.
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Old 04-26-2011, 03:04 PM   #33
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Lucky you: I was bored. I've got a very early 90, a 93, and a 94 here. The electrical connectors are identical on all 3 of them. My 99 is somewhere else...but it's an NB with an NB alternator anyways.
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Old 04-26-2011, 03:07 PM   #34
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you should put the 1.6L pulley on teh 94 Alt and then sell it to me cheap!
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Old 04-26-2011, 03:09 PM   #35
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That would involve me giving you the alternator off of my turbo daily.

The 90 is a parts car though...
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Old 04-26-2011, 03:39 PM   #36
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you should sell me the parts car alternator, cheap!
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Old 04-26-2011, 03:52 PM   #37
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i had the same problem on my '99, i just add two new ground cables & problem solved
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Old 04-26-2011, 04:27 PM   #38
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means I have to air up the tires, push it into the garage, pick it up in the air, get underneath it, remove the undertray, remove the alternator, put the undertray back on, put a warning on the battery cables, drop the car, push it back out of the garage, box up the alternator, shower as much crap off of me as possible, take it to the post office and put it in a flatrate box, and hope I don't get hurt doing it.

I'll do it for $45 shipped - not because I think the part is worth that, but my time is quite valuable, might be 2 or 3 days before I can get it out of the car.

Comes with a close-box guarantee. I guarantee it until I close the shipping box.

Up to you. The car was running before it was a parts car, but due to the PO being a CR.NET wannabe, he had destroyed it so bad that I deemed it irrepairable. It's the 203rd miata ever made per VIN
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Old 04-26-2011, 04:30 PM   #39
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damn dawg, last time I changed my alt it took me maybe 15 minutes...and I did it before going to work.
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Old 04-26-2011, 05:52 PM   #40
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Mine kind of acts the same way and I have the stock ECU. When the a/c first comes on the idle will drop way down and then slowly recover. I put in a new alternator and battery less than a year ago. I just don't worry about it, I'm glad my a/c actually works.
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