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alternator issues

i just put a new voltage regulator(i think thats what its called) into(onto) my alternator, got a fully charged battery and voltage meter on dash still only reads about 12 AT IDLE and not much more at speed! what gives? is this normal, am i missing something else, please let me know as i would HATE to be out one night and have battery failure
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wjcoleman
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"8's and lookn 4 da "7"s
Old 06-19-2010, 12:27 PM
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just put volt meter on it and it registers just under 12.5 volts at the battery , so then i went to post under hood and it read the same, so is alternator shot or am i missing something
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wjcoleman
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"8's and lookn 4 da "7"s
Old 06-19-2010, 02:16 PM
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There is a bulb in the dash, charge warning or some such, Porsche originally made that part of the alternator exciter circuit. Downside is bulb burns out, alternator doesn't charge.

See if the exciter circuit or that bulb is working, comes on normally when car starts.

928 dash problem
Old 06-19-2010, 03:06 PM
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You may have a bad diode or a bad winding in the alternator itself. The alternator should give you 14-14.5 vdc at 2000 rpms or greater..... if all is well. The built in voltmeter on the dash can be affected by a connection on the pod where the flexiable circut board plugs into the wiring harness or a bad ground. But, since you have read the voltage at the test point and it is 12 vdc or maybe 12.5 at say 2000 rpm then the alternator itself is highly suspect.

Jim
Old 06-19-2010, 04:52 PM
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interesting read!!!! problem is all lights work on thier prospective units, and the red light at the end (below ten) works also, it was the last thing i saw befor car fell dead, which made me think alternator, then everyone talked me into voltage regulator and now i feel like i just made dumb move and still have to buy a alt from somewhere! will buying new (reman) alt solve my somewhat chaRGING ISSUE, CAN I TRUST THE GAUGE ON THE SIDE, any more help is appreciated
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wjcoleman
84 928
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"8's and lookn 4 da "7"s
Old 06-19-2010, 07:13 PM
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do you have a hot post cover??
Is the 14 pin connector clean from corrosion its just above the hot post. Are the wires correctly attached to the alternator?
do you get 12v on the small wire with the key on??
disconnect the wire from the alternator first to check. If you are getting 12v on the small wire then you have a problem with the alternator. The 12v is the exciter circuit this turns the alternator on to charge. I had a similar issue and the blue wire was sheared about 4 inches from the end where it came through the grommet of the rear alt cover
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Old 06-19-2010, 09:12 PM
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update,
went to battery, test light (good) volt meter at battery(12v), went to post under hood, test light ok, volt at post(12v), crawled under car test light at alt(good) test volt at alt car off (12v) start vehicle test at alt still 12 V, go to back of car again and while running disconnect the positive and car dies , dammmmmnnnnn, any more suggestions or is it just new alt time!
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84 928
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"8's and lookn 4 da "7"s
Old 06-20-2010, 07:49 AM
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warning do not disconnect the battery while the car is running you can damage the alternator and or the engine computer
To test the small blue wire at the alternator it must be disconnected first,
to see if your getting 12v, with the key in the run position engine not running
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Old 06-20-2010, 08:50 AM
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Yikes, you may have toasted your electrical system - the expensive stuff too. I always extensively research first, before I start turning any wrenches.
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Old 06-21-2010, 07:17 PM
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I just posted on your last thread. check here

alternator issues: update
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Old 06-21-2010, 07:38 PM
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At the T14 (14 Pin connector) Top PIN #1 (p1)is the exciter lead (blue but can look black) from the Alt D+. This pin connects to the bottom ot the T14 (p1) and goes to the CEP plug O8 which connects to Z1 on the Board and a black wire on the back goes to Z6.

As MrMerlin suggests, test the Alt and check the above contact points for any voltage delta...
Jon
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Old 06-22-2010, 11:02 AM
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gauge flickers up and down or ticks is a better word when using turn signals, i will clean all contacts and get 'better' voltage readings tommorrow, if the look or stay the same as posted, i will start my search for an alternator, dont want to spend to much time on a bad alt! i wanna drive and enjoy
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wjcoleman
84 928
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"8's and lookn 4 da "7"s
Old 06-22-2010, 07:17 PM
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I got a rebuilt alternator for my '84 from Advance Auto Parts. $130 with a $40 or $60 core charge. They shipped it for free to the store from wherever it was (think it may have been international judging by all the air mail stickers on it and the fact that it took 6 days). Don't forget to save your alternator pulley, fan, and spacers, etc. I forgot to do so and drove back the next day to reclaim my pulley before the core was shipped off and gone forever (new pulley costs ~$160). So far I have no complaints, the rebuilt unit has worked just fine. The bad unit caused a bunch of wierd problems, such as all the warning lights flickering on and off intermittently, and the cold start system holding the engine at a higher RPM longer than usual.

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Old 06-23-2010, 04:27 AM
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battery still(uncranked)12.75v, post under hood(uncranked) 12.75, star car 12.27v at battery and same at post under hood!!!! , will order alternator tonigh when i get a break! how laborous is it to replace, or is this a "shade tree mechanics type job"? i need to know 'cause i dont have no shadetrees lol
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"8's and lookn 4 da "7"s
Old 06-23-2010, 12:54 PM
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One jack stand...two hands. In most cases use your original pulley.
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Old 06-23-2010, 01:09 PM
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Now, these battery voltages...you had the battery compartment open, and you were holding down the prongs on the top of the battery when you did this right?

Engine on: You should see about 13.7 volts while the engine is idling, and all the dash lights are out.

[the Motorola alternators on '84 and laters cars will NOT "ignite" at start up. There is another Porsche website where this was addressed, but it involves pulling the voltage regulator apart and changing a diode. A lot of work!]

All you need to do with an '84 or later car is rev the engine above 1800 rpm and your alternator will start working. For what it is worth, I owned a '77 VW Rabbit, an '85 VW Scirocco, and my current '85 928S2; all had the exact same alternator, all did the same damn thing. Between the '85 Scirocco and the '85 928S2, I owned a '92 Corrado SLC which had a different alternator that DID NOT have this odd characteristic. This 115 amp Denso alternator should be adopted by the 928 community as our official alternator!

=======

First of all, CLEAN ALL YOUR CONTACTS. I don't care if you cleaned them last week when you went to start the car....clean them again. Now, go around and clean all the ground contacts. There are two above the fuse box, one at the rear of the car where the negative ground strap connects, and two under the engine. I think the main engine connector at the right front of the car, just behind the right headlight. Pull it apart, clean everything with ultra-fine sandpaper and Deoxit cleaner, and put it back together.

NOW: When all this is done, start your car, and check your voltage at your battery.

Does your cockpit gauge say the same thing? The gauge in the cockpit is NOTORIOUSLY inaccurate! DON'T rely on it. Rely on your multi-tester. If your multitester shows 13.7 volts at idle, and your dash gauge shows something else? Pull the gauge cluster, carefully remove the needle of the voltage gauge with a pair of needle-nose pliers...and glue it back in place in such a way that it registers 13.7 volts when the engine is on. Why? Because the cockpit gauge is ONLY usefull for trend information. If it is normally 13.0 volts, then one day shows zero....you know you need to check the system before leaving the house. THAT is the reason this gauge exists on our gauge panels- trend, not actual information.

N!
Old 06-23-2010, 03:37 PM
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thanks guys i will give it the old heave-ho one more time!!!! so normy as a replacement should i be looking for a stock 90 amp, replacement or this 115 that you speak of and would it fit without any major modifications, and does a higher amped alt have any issues that need to be addressed, like overcharging over heating etc,
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"8's and lookn 4 da "7"s
Old 06-24-2010, 04:16 AM
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Quote:
Originally Posted by Danglerb View Post
There is a bulb in the dash, charge warning or some such, Porsche originally made that part of the alternator exciter circuit. Downside is bulb burns out, alternator doesn't charge.

See if the exciter circuit or that bulb is working, comes on normally when car starts.

928 dash problem
Nice find Mike D! I have been trying to find that d*** bulb for a year; took the pod out three times looking for it. The write-up you posted says you get to it from the FRONT of the cluster by pulling the gauge off. All the rest of the bulbs are connected to the BACK of the cluster. I can finally get my alternator exciter circuit to work now! I let Roger know I need that bulb this morning, so I should get it very soon.
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Old 06-24-2010, 08:52 AM
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Quote:
Originally Posted by wills928 View Post
thanks guys i will give it the old heave-ho one more time!!!! so normy as a replacement should i be looking for a stock 90 amp, replacement or this 115 that you speak of and would it fit without any major modifications, and does a higher amped alt have any issues that need to be addressed, like overcharging over heating etc,

I went with the 200 amp because I am installing a good stereo, amp, and sub along with new speakers. I also thought that I couldn't hurt but LORD THUNDERIN is it pricey
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Old 06-27-2010, 05:28 PM
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Been there done that, too old for the thundering these days, plus I get enough. Loud music when I work! Don't need it in my car
Old 06-27-2010, 06:31 PM
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