Low Voltage
05-31-2009, 08:27 AM
#1
2nd Gear
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Low Voltage
I have an 85 auto with 90K. My low voltage light comes on at idle with the AC on or several different accessories are running. I have tried a new alternator and all of the moving componets on the front of the engine have been replaced. It drops down to about 11.3 on the guage. It doesn't really bother me, but I am getting ready to sell the car and am afraid it will turn off a potential buyer.
What makes the idle kick up when the AC is turned on?
Would a undersize alt pulley help?
Thanks!
What makes the idle kick up when the AC is turned on?
Would a undersize alt pulley help?
Thanks!
05-31-2009, 08:58 AM
#2
Le Mans Master
If the light goes out when your idle picks up a little it may be idling to low. You may need to reset your base idle, instructions are on here somewhere. My auto trans 89 idles at around 600 rpm in gear.As for your question about the air conditioning, I believe the IAC opens up to compensate for the extra drag from the compressor coming on ...WW
06-02-2009, 02:07 PM
#3
Pro
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How
I have an 85 auto with 90K. My low voltage light comes on at idle with the AC on or several different accessories are running. I have tried a new alternator and all of the moving componets on the front of the engine have been replaced. It drops down to about 11.3 on the guage. It doesn't really bother me, but I am getting ready to sell the car and am afraid it will turn off a potential buyer.
What makes the idle kick up when the AC is turned on?
Would a undersize alt pulley help?
Thanks!
What makes the idle kick up when the AC is turned on?
Would a undersize alt pulley help?
Thanks!
06-02-2009, 03:08 PM
#4
Le Mans Master
There is no way to change idle speed. If it isn't hitting +/- 50 rpms of Targeted in Drive or +/- 100 rpms in Park/Neutral, then something else is going on. Of course you need to scan it to see what it's doing.
This looks like a load issue so something is either drawing more than it did when it left the Factory, or the harness has so much resistance in it, it's time to pull it out and put in a new one. I'd start at the Blower Motor. Examine the connector for discoloration and/or feel it for heat. Either would indicate a voltage drop or a tired motor that's sucking the life out of it. The drop can be stopped by taking apart the weather pac and soldering the terminals, but you might just solder in a new connector. You'd need a Clampon to measure draw as tired motors can pull 25 amps or more, but if you don't mind replacing the fuse in a DVM (because most max out at 20 amps), you could hook that up. If the fuse blows, replace the motor.
This looks like a load issue so something is either drawing more than it did when it left the Factory, or the harness has so much resistance in it, it's time to pull it out and put in a new one. I'd start at the Blower Motor. Examine the connector for discoloration and/or feel it for heat. Either would indicate a voltage drop or a tired motor that's sucking the life out of it. The drop can be stopped by taking apart the weather pac and soldering the terminals, but you might just solder in a new connector. You'd need a Clampon to measure draw as tired motors can pull 25 amps or more, but if you don't mind replacing the fuse in a DVM (because most max out at 20 amps), you could hook that up. If the fuse blows, replace the motor.
06-02-2009, 10:16 PM
#5
Race Director
I have a lot of recent experience with this.
My '85 was munching an alternator every 6 months. If it got above 85, i knew the alt was toast that day. They used the thinnest cables possible and they naturally corrode and lose conductivity over time.
Answer:
1. Run a ground line from the back of the alt (where the rear brace attaches) to the frame ground under the battery.
2. Run another 8 ga line from inside the Batt boot to the positive terminal of the battery. Buy a post mount if you wish for both the batt and the ground.
3. I took my SI alt to a rebuilder and had him mod it to a 140 amp. Could have got a CS, but why bother with the adapters and bracketry changes? Price becomes a wash.
4. While the battery is out for accessing the ground, have it load tested.
My '85 was munching an alternator every 6 months. If it got above 85, i knew the alt was toast that day. They used the thinnest cables possible and they naturally corrode and lose conductivity over time.
Answer:
1. Run a ground line from the back of the alt (where the rear brace attaches) to the frame ground under the battery.
2. Run another 8 ga line from inside the Batt boot to the positive terminal of the battery. Buy a post mount if you wish for both the batt and the ground.
3. I took my SI alt to a rebuilder and had him mod it to a 140 amp. Could have got a CS, but why bother with the adapters and bracketry changes? Price becomes a wash.
4. While the battery is out for accessing the ground, have it load tested.