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*Searched* Alternator not charging battery

84' 944. Ok, I have searched numerous times and came up with no results. Brand new Bosch alternator brand new Optima battery (Red top) changed the alternator and voltage stays at about 11.5 for a few min then lower and lower. Thought they sold me a bad alternator so a exchanged it for another one, SAME THING. Alternator light is good and I also bypassed it by putting one side of a dome lightblub on the alternator post and the other side on the positive side of the battery. when I take both cables off of the alternator and let it run by itself it puts out 16 volts!?!?!?!?! when the cables are connected to the alternator it will sometimes go to about 12 volts when I turn the lights on it drops to 10.4. THE BIGGEST thing is that when I rev it the voltage goes DOWN!?!?!?!? don't get it.

Old 10-22-2007, 01:50 PM
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Trusting the stock gauge, or are you using a DVM(Digital Volt Meter)?
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Old 10-22-2007, 02:36 PM
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weak/broken grounds, weak alt-battery link

take resistance readings from various points like battery neg to engine block and battery pos to alternator contact. I'd assume one of those will have a high resistance which would explain your voltage loss

before anyone else gets to say it, clean all your ground connections. That's the one of the simplest yet overlooked source of electrical gremlins.
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Old 10-22-2007, 03:03 PM
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Yes, I am using a DVM, 84's don't have stock gauges. Thanks a lot for the replys. Ok would a bad ground be the reason for the voltage going down when it bring her up to 2 grand? For some reason I have a feeling like it is a problem with one of those red wires I don't know why but I just have this inclination that it could be.
Old 10-22-2007, 04:20 PM
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Oops I almost forgot, What ohm setting would I use to take resistance readings? I have never used that part of my DVM, never really had the pleasure of diagnosing an overly complicated Porsche charging system.
Old 10-22-2007, 04:26 PM
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The Porsche manual says never run your car without a battery hooked up. This will blow out your computer and more trouble will come. That said, I do not know what would happen when you take off the cables to your alternator, let us know. Now, since the alternator output goes to the starter first, clean the starter connections. If this does not solve the problem, run a thick cable from the alternator directly to the battery from the alt output post (last resort). Clean your grounds on top of the bell housing. Frustrating isn't it?

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Old 10-22-2007, 05:13 PM
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Yeah, I feel like setting the 944 on fire right now. Alright, I ran a 2 gauge cable from the alt. post to the positive battery connection, and again from the negative battery post to the block.
Old 10-22-2007, 05:36 PM
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Quote:
Originally Posted by SvoRx7Power View Post
Ok would a bad ground be the reason for the voltage going down when it bring her up to 2 grand?
As you increase RPM, you increase the load the engine pulls. You've doubled the injector pulses and ignition fires as well as various other off idle processes.

As for ohm readings on wiring, anything over 50 ohms should be cause for concern. Another way of going about it would be to test voltage drop directly with the engine running.

While the engine is idling, take measurements of the battery itself. That's your baseline. Testing pos to body/engine block/whatever should give you the same reading. Wherever you find a sizable drop is your weak link.

also to note: Since you don't have any starting issues, i'd suspect the link (as someone else pointed out as well) from the starter to the alternator.
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Old 10-22-2007, 07:16 PM
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not much time, haven't read all the responses, but it sounds like you replaced the alternator twice and didn't get the battery bench tested.

pull it and take it to a store to get tested.

if you've done that and i didn't read it, apologies, and ignore me :P
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Old 10-22-2007, 07:40 PM
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The battery is new and the ohms tested out at about .53 and sometimes would go to about .6 or so I don't know wh
at I'm going to do.
Old 10-23-2007, 08:47 AM
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Car turned off, you should measure ohm load between the neg. terminal of the battery to the engine block. In a perfect world, you should measure 0.000 ohms.

On my '83 I just measured .1 ohms, from terminal to block.
On my '86 I measured 1.0 ohms...... I need to replace the cables on this car pretty bad.

If you attempt to measure it with the car running and things turned on, you'll get a variable reading, so it's best to have the car shut down, and nothing on(dome light, etc...)

Since you are working on an '84, it's pretty easy to replace the cables. Start with the neg terminal to ground in the battery box, then replace the neg terminal to block(back of head). 6g wire is adequate, but I prefer 4g wiring.

Also pay attention to what your DVM is telling you. Make sure the reading is in ohms only, not megaohms(denoted by an M on the display). Megaohms would be bad and pointing to a problem.

Post up info on your DVM so that we can tell you what setting to use, should be a 2 or 20ohm setting I believe. I have a Fluke, so it self calibrates just using the simple Ohm setting.
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Old 10-23-2007, 02:48 PM
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I have a cheap ohm meter from pepboys and i use the 20 ohm setting also.
Old 10-23-2007, 11:03 PM
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Okay, and now I am having some crazy issues, I got pissed off and riped all of the fuses out and now everything is okay. So I then nailed it down to one fuse, It was the ac blower motor fuse that somehow controlled the cooling fan???? I pulled the cooling wire off and and wired it up to a switch. Okay the alternator is charging the battery and the voltage goes up to 14.something and holds when I rev it. When I turn the fan on its fine, when I turn the headlights on It's fine, when I turn them both on all hell breaks loose and the same problem that I had before is back. Thanks for all the great tips
Old 10-25-2007, 09:27 PM
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good job.

clarks-garage has a lot of info, this is one of the things covered, pulling the fuses one at a time.
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Old 10-25-2007, 09:39 PM
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Quote:
The Porsche manual says never run your car without a battery hooked up. This will blow out your computer and more trouble will come. That said, I do not know what would happen when you take off the cables to your alternator, let us know.
In case anyone's wondering, these cars work just fine without an alternator installed, and the engine electrics draw very little current. I know because I had to drive an hour home, then to the parts store and back without an alternator, and it was fine.
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Old 10-25-2007, 10:33 PM
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+^^

battery only, with no alternator - OK (most race cars run this way)
alternator only, with no battery - BAD
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Old 10-26-2007, 12:54 PM
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hmm thats awesome that makes me feel so much better. So what are your cars running does it run at about 14.5 like it should or is it somewhere around where mine is like 13.something sometimes it goes up and sometimes it goes down defiantly when I turn both my fan and headlights on. Also has anyone heard of the a/c switch turning on the fan? Or did someone just jerry rig the McBadballs out of it?
Old 10-26-2007, 02:29 PM
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sounds like something is open (disconnected) or hooked up wrong, possibly with the circuits you seem to have isolated. I'm an electrician and i find troubleshooting automotive electrical problems daunting! careful methodical checking and double checking will eventually uncover your problem, and as suggested check the garage shop manual at clarks'-garage. i just fixed a no charge problem by replacing the brushes in the alternator of my'87, would have had no idea about that without this forum. good luck
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Old 10-26-2007, 02:55 PM
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Free advice. No charge.

Quote:
Originally Posted by SvoRx7Power View Post
A...So what are your cars running does it run at about 14.5 like it should or is it somewhere around where mine is like 13.something...

B...Also has anyone heard of the a/c switch turning on the fan? Or did someone just jerry rig the McBadballs out of it?...
A Normally, charging voltage should be 13.75-14.25VDC depending on what you have turned on. Measure this at the battery.

Big loads are:
- rear defogger which includes the heated mirrors and windshield squirter heaters
- A/C which includes BOTH radiator fans, evaporator blower and A/C clutch
- headlights and fog lights (my only real complaint about Porsche 924/944 design is the wiring scheme for these lights)

B The A/C switch turns on all the radiator fans by design.
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Old 10-26-2007, 05:03 PM
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Big loads will drop the voltage. You may not have a problem with the lights or the fan. If there is resistance in the path from the alternator to the battery then the battery will not maintain voltage when you load it up.
Go back and look for bad wires or bad connections from the battery to the grounds and the battery to alternator. My money says this is a real simple problem with some wierd symptoms. Don't get spooked, stick to the basics.


Good luck
Jon

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Old 10-26-2007, 05:19 PM
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