Greetings!

I am getting a voltage drop on my battery guage while driving. The car is warm and runs smooth. The drop can dip as low as 9-10 and then will eventually jump back to just under 13. (don't know how accurate the dash guage is. What should it display when ALT is charging?) Also the check engine light goes off and on intermittently but does not coincide with the voltage drop. I don't have a code reader so bear with me. I can hear a bearing going bad in the ALT when I put my stethoscope on it, so I am probably in for a new ALT anyway but I wanted to hear from you guys if this is something more. Thanks for any input.

 

Bad alternator, car is drawning off the battery and not charging.
Soon you will find yourself stranded.

 

That's all for me. New ALT, order up!

 

does the rpm suddently drop too, like if the car was going to stall?

 

Thats the end result when the battery power gets to low from not chargings to met engines electrical demands,

 

Now I am scratching my head. I installed the new alternator and even replaced the battery just to be safe. (It was old and had been drained down to nothing at one point). My first drive had the needle at 13 volts and after about 5 miles, it began to drop down to about 12. After stopping and then restarting, it dropped down to 10. Then the check engine light came on and the voltage continued to stay around 10. Then it climbed back up to around 12. What is happening here? It seems the ALT is not able to charge. Is there a fusible link or sensor that could be crapped out? I thought that the dash guage should read steady but then again I haven't been watching it as closely as I do now. Any ideas?

 

Check the cable between the battery and the alternator. Also the red wire that runs from the alternator to the starter solenoid, it is a fusible link. If you have changed the alternator and battery and still have this problem, it is time to start looking at the wiring. You might also check the tension on the fan belt to be sure its not loose and slipping under load. Also check your cable connections at the starter solenoid.

 

Well, I took my car by AdvanceAuto and had them test the battery and ALT. It was puting out 13.8 volts but my guage was showing 9. I reached in and tapped the guage with my finger and it jumped up to 12! It still isn't displaying what is shown at the battery so I don't know what it could be. I did make sure to check all the fusible links and took off the connectors to clean them and make sure everything is solid and tight. I drove home and even though my guage was showing 8 (normally sending me into a panic) I just cruised back and left it running while I checked with my voltmeter. It showed 13.8 just like at AdvanceAuto. Very frustrating to say the least. I guess I'll just throw the jumper cables in the trunk and just rock on.

 

Couple of things to do. First, pull the instrument panel trim piece and the plastic cover to get access to the guage. Remove the small fasteners that hold the guage and gently pull it foreward and out. It uses the threaded posts on the back of the guage to make contact with the fingers on the cluster pc board. On the back of the guage you will see 2 nuts attached to a small ceramic block. That is a resistor. Remove the nuts and look at the contact surface where they attach at the resistor. If it looks black gently remove it from the guage and clean the contact area with a pencil eraser or contact cleaner or alcohol till it gets shiny. Reinstall the resistor back on the guage and tighten the nuts, don't overtighten them or you can crack the resistor. Clean the post threads with alcohol or contact cleaner and gently tighten the fingers a little and reinstall the guage. In some applications the guage is in series with the generator sense line and it will cause low gen output. Also check the fuse in the fuse panel labeled "chg/fan" and make sure it is not burnt or corroded. Typical voltage should be around 14.5-14.8 volts after a cold start and they will generally stay around 14 when running. Hope this helps.

 

I tripped when that first happened to me in my 89 IROC but turned out to be the radiator fan turning on. Voltage dipped down but then went back to normal. At first I thought it was my window switches because the first time it happened I was putting the windows down hahaha (same day I bought the car). But after I watched the trend I new it was the fan. Maybe check if any of your accessories turn on when it happens?