Question: Low Voltage

[vdogamr]

So first and foremost... If the voltage gauge dips down to 12.7, that is too low right?

So the other day I was driving at night and I could tell the instrument cluster was occasionally dimming. I flipped over to display battery voltage, and my volts were consistantly in the 13s (which may be low but, high 13s is normal for my car). Then, this past weekend, I was just driving around and when I would stop at red lights the voltage would dip down into the 12s. The volts did not seem to go up and down parallel to revving the engine.

Either way, I took the battery and the altenator to the local auto supply store for testing and they both tested great. The altenator should be fine it was replaced 3 years ago (< 15K miles). I know the voltage regulator in an 88 Corvette is in the altenator, and again it tested fine. The only idea I have left is to put it all back together and make sure the drive belt is tight.

Any ideas would be very helpful. Thanks in advance.​

 

[TedC]

Those voltages are not right. However, what the cluster is posting may not be the same voltages that your car is running on. Measure the voltages at the battery to confirm. Turn on the headlights, what happens? I see around 13.8V when the battery is charging off the alternator. The digital cluster used on early C4s is prone to connection and power capacitor issues. batee.com - C4 Corvette Digital Cluster Instrument Gauge Panel Repair Guide 1984 1985 1986 1987 1988 1989 Repair Cold Solder Joints Missing Dead Segment Dark

 

[vdogamr]

I intend to put it back together tonight. I will test the voltage at the battery as you suggest. I will also turn on the headlights, but what do you expect to happen? What would be fine/bad? My thought is that nothing noticable should happen if everything is working fine. (other than the lights comming on )

I know the site you linked to very well, and I hope he never removes it. I once tried to follow his guide to fixing the dark bars. Don't know if I missed something but nothing changed. The cluster was so difficult to disconnect, remove, and reconnect, I just left it. But I did replace the bulbs with the ones suggested to produce less heat.

 

[John Robinson]

There is another possibility which is the instruments in the car may be failing. Here is a little trick I used to find out that both my volt reading were not right.

Radio Shack sells a cigarette adapter that I used to wire in my digital volt meter whcih gave me another source of readings.



Basically this is the same as connecting to the battery direct but gives you the ability to observe the voltage as you drive etc. In my case I discovered that the two volt meters in the car were not even close and the shown fluctuations were in fact not happening at all.

 

[TedC]

I like John's suggestion. They you can drive and compare. Headlights draw lots of current. Based on your posted voltages if these were true system readings then the lights should go dim.

 

[vdogamr]

Sorry it took me so long to reply. The only voltmeter I had was analog, and that is a little hard to read while driving.

So, just like trying to diagnose any car problem... It doesn't happen when you are watching. During this first test drive, the voltage on the dashboard never dropped below 13.3. In general the digital voltmeter read about .5 higher than the dashboard. Turning on the headlights resulted in almost, but not quite, a .1 volt drop. I can't tell if the headlights are dimmer than normal. The voltmeter never read more than 14.1, so I guess it is good that I am not too high.

I will drive it around more with the voltmeter hooked up and see if I can reproduce the issue. In case it matters, I just wired the voltmeter straight to the battery terminals.

As a side note: I don't know if Tension Arm is the right name for the pulley on the drive belt, but even after tightening the bolt as much as I could I can still move the pulley by hand. Not effotlessly, but easier than I think I should be able to. Is it possible that the bolt is no longer working? I don't hear squeaking or anything to make me think the belt is slipping, just seems wrong.

Thanks