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Old 04-18-2005, 12:52 PM   #1
sps SOHC
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Default Failing alternator?

I must admit that I do abuse it w/ my system and all. So I think it's going down hill.
Last night, parked in my driveway, I started the car, RPMs were about 900 or so. I turned on the lights and you could hear the rpm drop a tiny bit and then back up. Same when I turned on the brights and put on the brake. So the smallest little extra demand for electricity seems to affect the alternator more than it should. I have never noticed it before. Maybe it is normal.

Also when I'm driving (when the car is warm) and I slow to a stop and put it in neutral the RPMs drop to almost nothing and then rise back to idle at 500 or 600. This may be because something else, I'm not sure. Once in a while it seems like the battery is struggling extra hard to start the car, like it didn't get fully juiced up before I shut it off.
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-96 SC2 gets 35 mpg mix city/hw.
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Old 04-18-2005, 04:43 PM   #2
austin71184
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Default Re: Failing alternator?

if you have a multi meter measure voltage across the battery while the engine is running........should be in the mid 14 volt range. Although the step before is ok doen't advance auto parts wheel out vat-40's (starter charger battery) tester right to your car for you ??????
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Old 04-19-2005, 09:38 AM   #3
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Default Re: Failing alternator?

Quote:
> sps SOHC <
> So the smallest little extra demand for electricity seems to affect the alternator more than it should. I have never noticed it before. Maybe it is normal. <
Yep, for atleast in my case, noticed such variation in RPMs from day-one... has always happened, with no change even when replacing the alternator ....
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> 95 SL 2 = 653,369 Miles 40.4 MPG, as of 5/20/11. My manual Radiator Fan Switch, courtesy of Wolfman's patient installation guidance, continues to be.......invaluable < The car was retired
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Old 04-19-2005, 12:34 PM   #4
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Default Re: Failing alternator?

oh, and my capacitor will not charge fully. It goes to about 9V when the car is running. But maybe my capacitor is busted...I hope not, it's a nice one. Or was....
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Old 04-21-2005, 07:38 PM   #5
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Default Re: Failing alternator?

Well SOMETHING is sure messed up. Cuz I'm sitting at idle, the car is warm, my steering is almost cranked all the way left, I turn it some more in that direction and the idle drops so low the car almost shuts off and didn't pick up until I stopped turning. It was ridiculous. Power steering runs solely off the belt? What does this mean? I am convinced if I kept the wheel turned all the way the car would have stalled out.
I'm confused.
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Old 04-21-2005, 10:58 PM   #6
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Default Re: Failing alternator?

First, it is normal for a slight rpm drop when any electrical load is applied because the alternator becomes harder to turn. This should be quickly compsenated for by the PCM when it sees the RPM drop. The bigger the load, the harder the alternator is to turn. Also the power steering pump represents a mechanical load when asked to do it's job a bit harder such as taking the steering to its stops and holding there.

As for the battery/charging issue. Like a previous post, a simple volt meter across the battery while it is running should indicate a bit over 14 volts. You mentioned that you have a capacitor. I presume this is for a high power sound sytem. Actually a capacitor in this application is supposed to compensate for sudden electrical loads untill the voltage regulation circuits in the alternator can catch up. Because in electricity, the capacitor does not know what device on the car is suddenly asking for more current, it really wouldn't matter what electrical load you applied. It is going to dump its reserve into the electrical system unless you have them isolated with devices such as diodes.

Somthing else to consider. You said the capacitor is only being charged to 9 volts. A capacitor is only going to be charged to the voltage of the system providing the charge and depending on the capacitors condition. It possible that the capacitor has developed a high resistance short internally. This could have two results. One it would keep the capacitor from reaching its full potential and two, a short is a short is a short and depending on the value of the short (high resistance vs a dead short, in which case you would probably have smoke) it will eventually drain your battery. Also capacitors can not be checked with standard ohm meter other than to determine whether or not they are in fact shorted. BUT when first attached, an ohm meter will have an initial deflection and then return to "no continuity" because the battery in the meter is "charging" the capacitor and seeing an initial flow. Once charged, the meter will then show no continuity. If it shows any continuity after the initial hook up, the capacitor is shorted. CAUTION, certain capacitors are polarized electrolytics. IF HOOKED UP BACKWARDS,THEY CAN AND OFTEN WILL EXPLODE. I remember in my basic electronic training when we had to build small shop projects, more than one electrolytic capacitor met its doom this way. The student looked like Wylie Cyote still holding the burned match after the ACME device exploded.
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Old 04-22-2005, 10:32 AM   #7
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Default Re: Failing alternator?

Gotta find my multimeter...

I don't know for sure that its the alternator but I don't think my car should chug and die when I crank the wheel all the way.

Thanks for the input. I capacitor isn't connected since it wouldn't fully charge. I'll try to charge it on another battery or somethin, but I'm thinking it's probably gone.
It was a nice capacitor too. 2.5 F Kole Audio.

I'll try to find the multimeter tonight.
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