Charging System


Low Gauge Voltage
Current Drain Troubleshooting

Low Gauge Voltage

"I have had a low voltage reading after engine start-up on the IP gauge since buying my Fiero years ago. The reading is at about 12v, and the "volts" idiot light is on until I throttle it a little. After this, all's well."

With this type of problem, it's important to determine whether there really is a charging problem, or if its just an innaccurate gauge display. The way to do that is with an accurate (DVM) digital voltmeter; these relatively inexpensive multimeters are available at Radio Shack, electronic supply places, etc... BTW, the volts light NORMALLY goes off as soon as the engine fires up, even idle is enuf.

I just measured my car. At high idle, (1500 RPM) no accessories on, the voltage is 14.3 volts. I'd say anything lower than 13.0 volts is too low, and there is a problem, either the voltage regulator, or the alternator.

My experience with alternator failures has always been worn brushes, which results in no alternator output. The charge light stays on continuously, and your battery runs down to nothing (eventually).

However, alternators produce three phase AC voltage, with three separate windings, each connected to two diodes. I've heard of individual diode failures, which can cause 16.6% (1 diode) or 33.3% (2 diodes) of the alternator's output to go dead. My gut feeling is this might affect output current capacity (amps) more than voltage, but I don't know for sure-no real experience there.

Voltage regulators can "go" three ways. One: completely dead, and no charging occurs. Two: shorted out, and the alternator charges full tilt, all the time. This happened on my motorcycle; not a big problem, for short trip, in town use, but on the last two 400 mile days of my trip, boiled my battery dry (threw that one away!) Finally, they could go out of adjustment, and maintain the battery voltage at a too low or too high voltage; this is theoretically possible, but I've never heard of it happening.

Get an accurate DVM, find out what your charging system is doing, and troubleshoot from there, if necessary. Just my 2 cents worth, for this week, and probably more than you ever wanted to know about alternators and voltage regulators!

From: Paul Millette

Current Drain

>I've checked my alternator output, and it is OK, and my battery will
>charge up, but anytime my car sits overnight, my battery is always
>run down.
You want to set up your multi-meter to read current. Not knowing what kind of meter you have makes it hard to tell you how to do this. Some meters you have to physically move the test leads, others you turn (push) switchs. Disconnect one lead from the battery. Place the red lead on the battery post that was just removed; place the black lead on the cable just removed (the metal part). The colors are the multi-meter leads. Always start with a high scale and work down. Any current over a few milliamps indicates leakage. Make sure all electrical loads are off (don't forget the trunk light, you've got the engine lid up, right?). If the meter reads in reverse or reads negative, reverse the leads.

Don't forget to revert back to a "voltage-mode" on your multi-meter when you're finished or you'll blow the rascal next time you go to use it to measure voltage.

From: Tin Man

Online Service Guide Main Page

Date: Mon, 16 Sep 1996 17:25:38 -0500 From: "Mike Mohr" To: Subject: Missing in engine and wacky tach Message-Id: <> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit I talked with a couple of you about the problems I was having with my 86 SE V6 5speed...I had a bad miss at anything above 2500 rpm, and the tach was jumping all over the dial. I can't remember who it was, but a couple of you had the same problem as I . I replaced the distributor cap, the rotor, the coil, the plugs, etc. to no avail. I had the ignition module checked out, as Tin Man pointed out...nada, it was good. One night, when I went out to try and start it, it wouldn't even turn over...this was the night I replaced the coil. At this point, it started and ran beautifully when cold, but once it warmed up, the symptoms returned. Finally, I bought a distributor from Paul Vargyas, who just happened to have one handy. If you remember from my first post, one of the stationary arms on the pickup coil was bent over at a 45 degree angle, and one of the tabs on the rotating assembly was bent. I straightened these, and thought that would fix it, but it didn't. I finally got around on Sunday to installing the distributor that Paul sold me... VOILA! It worked! I had my doubts about it being the distributor, as it ran fine when cold, but apparently the bearings were worn just enough that when it was cold, they'd hold the shaft fine, but when it warmed up, they'd loosen up and let the shaft wobble. Put in the new one and everything was just fine...just that nice V6 burble at idle at any heat range, and no miss at high rpm; Anyway, if you're having the same problems I did, have your distributor checked out. I couldn't feel any play in the shaft, but it was there.... Thanks again, was greatly appreciated... Oh, I also saw a posting in here once about Delco plug wires priced at $70 a set from the dealer. I got a set for $35...go figure.... Mike Mohr Fremont, Nebraska 86 SE 2M6 V6 5 Speed ( "an' we're....back on the roooooaaaad agin....") 94 Grand Prix SE (B4U Package) --- Oh yes, you did ask about high charging voltage. You may experience high charging voltage just after starting that should start to normal out around 13-14 volts. If it remains high, yes, you probably need to dismantle the alternator to replace the regulator.