Voltage guage reads irratically....DESPERATELY need fast help!

[markjs]

I noticed this morning that my voltage guage is reading wildly. I recently replaced the Alternator with one from a wrecked Suby. For a couple of days things have been fine but this morning it starts reading like 10 volts and now at idle it reads at the bottom of the scale (8 volts). When I test the battery with my voltmeter, it reads 12.99 with the engine off, and 14 idling at about 800rpm with nothing on and just over 12 with everything on. With everything on if you take it up to 2000+ RPM it reads around 13.50 to 14. My haynes manual is terribly vague about this subject. The guage is making me very nervous is my job is newspaper delivery and I can't afford a breakdown on the job. I have a backup car but it's a gas hog and I need to avoid it if at all possible. Anyone have any ideas?

[idosubaru]

i'm guessing this alternator related. first make sure the belt is tight and not loose. make sure your crank pulley isn't separated. if you look carefully the crank pulley is an outer and inner metal ring separated by a thin rubber ring. if the metal separates from the rubber the inner metal part of the pulley will rotate and slip in relation to the outer ring. the outer ring won't spin nearly as fast and will cause charging issues which may start out as only lights on the dash going crazy. put a mark across the face of the pulley, run the motor awhile and then check it. if it's slipping the marks will no longer line up. fix temporarily with sheet metal screws or similar. battery terminals must be clean and tight.

 

check the alternator connections - the connetors there need to be clean and tight. they typically degrade and need replaced/cleaned.

 

if this all checks out, replace the alternator. autozone, advanced and others test alternators for free.

 

grounds have to be good as well.

[markjs]

Well after further testing the alternator holds a steady 14 volts when the lights and fan and all electrical is off, and the guage reads 12 even, but soon as you load the system with lights, heater and stereo, poof down to 12.40 volts. I also tried without the CD deck and just the lights and the heater make it sink. The guage reads lower and lower the longer it runs with electical stuff on. I suspect the alternator is bad and am headed out to test it post haste. I have another wrecked car to steal another alternator from, but theer's no telling how well it will work either. Unfortunately I simply don';t have the cash to replace the alternator probably til January.

[D-Cal]

Most of those readings sound normal for most cars. 12.5 with the car off, 14 while running. Have you considered that the gauge may be malfunctioning? Turning on heavy current accessories will cause a voltage dip in any car, and usually the ECM responds after a second by raising the idle RPM. I would trust your voltmeter readings across the battery terminals.

[markjs]

I took the alternator to be tested and it's bearings are shot so I suspect it is working somewhat but not properly. The guy wouldn't even test it, he said with the bearings that shot there was no point.

[idosubaru]

the lights coming on are a typical subaru sign of a failing alternator. i've ran for a couple months like this before....the lights come on, but everything else works fine, alternator, battery always charged, voltages good. it will gradually get to the point where loads make it worse (headlights, radio...etc), then eventually it will just go berserk with voltage spikes or fail. i put a new alternator in my car when my lights came on like this. few months later it failed and i had another one in the car to swap in. that's a terrible idea as with alternator failure you risk damaging at the least fusible links and possibly more. i was curious how long it would last (it was a few months, i was surprised), but best to replace it. your other used unit should work fine, i've had decent results with used units in the past.

[Cougar]

Since you were reading pretty good voltages at the battery but the dash meter showed a low reading this means that the power wiring to the cars accessories has a problem. The small wire tied to the positive battery post supplies power the cars accessories.

 

First, check all the fusible links for a bad connection. They are in the box mounted on the coolant reservoir. This is the most likely suspect of the trouble. You should measure each side of the links to make sure that they read close to the same voltage with reference to ground. I think the black link supplies most of the accessories though it may be one of the red ones that supplies power to the voltmeter.

 

If those things check out ok then try running a ground jumper from the negative battery post to the dash ground to see if that clears things up or, measure the voltage between those points to see if there is a ground problem. If you measure more than 0.2 volts then there may be a bad ground connection causing this problem.

[markjs]

I am beginning to wonder if I have a real problem at all. The alternator I am running checks out fine at NAPA. When the car is running with nothing on at idle I get a consistant 14 volts. The guage reads slightly above 12 when there is nothing on idling arond 850 RPM. As soon as I turn on the heater fan the voltage at the battery dips to around 12.4-12.9. It goes to 13.8-14 at 2000 RPM with everthing on. The guage reads under 12 when everthing is on at idle, like around 8-10 volts but the charge light does not come on. So basically same as before with the alternator with the loose bearings.

 

 

I asked one Auto parts store about the regulator because the Haynes manual says it can be integral to the alternator, or mounted on the firewall. I can't find it on the firewall at all. That store said it's inside the alternator, and I almost believe them because when you test votage at the terminal on the alternator, and grounded to its case, it measures about the same as at the battery. The other parts store told me the regulator is seperate, because they show a part number. I have not had the battery actaully go low enough not to start the car. I am just stuck and unsure because the guage had always worked before.

[Cougar]

It would be good to know what year and model car you have. I'm sure someone here could verify that the regulator is internal with that info provided.

 

It is pretty normal for the dash voltmeter to be around a volt lower than the charging circuit due to wire losses to the meter. The more things that are turned on, the more the loss will be. I would see what the battery voltage reads at idle using your meter and compare the dash reading with that. This will show you the amount of error between the two. It sounds like things are ok though the alternator is not putting out very well at idle. The idle RPM should be around 750-800 RPM.

 

If you want the dash meter to indicate better you will need to run an additional wire between the fusible link and the dash power connection. This will cut the wire loss down and increase the voltage to the dash. I would guess using at least 12 ga. wire would do the trick.

 

Another problem area that may be causing this is the connector to the ignition switch in the steering column. This is a fairly common problem.

[markjs]

It's a 1984 FWD 1800cc GL Wagon.

[D-Cal]

As long as the battery posts are showing ~14volts while running, you are charging the battery and should be fine.

 

If the measured voltage at the battery is below 12.5 while running with... say the headlights, blower and defroster on... a fairly common situation in cold climates, you might have a problem. It would take probably 10-20 minutes to drain the battery out though. I am not referring to idle, I am talking about cruise conditions.

 

Check around for corroded grounds as well, common culprit with electrical gremlins.

 

Try putting your meter across the pins feeding the dashboard voltage gauge and see what it reads. The problem could be purely the gauge, as I suggested above.

[zyewdall]

I would agree that the gauge is screwed up, and the alternator is okay. At idle with accessories on, I'd expect around 12.5. At 2,000prm or so, it should be above 13 with all the accessories on. More like 14 probably, but no higher than about 14.8 volts. If a voltmeter shows readings like this, the charging system is fine. Get a cheap multimeter and plug it into the cigarette lighter so you can check it while driving if the factory gauge is making you nervous (that's what I did on my truck).

[markjs]

It's ok, seems it got low and just needed to run a lot to get its charge back.