Idle Voltage
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Nope, the ECM has nothing to do with the charging voltage. The voltage regulator in the alternator attempts to maintain 14.7 volts across the battery (alternator cold) and 13.7 volts (alternator hot). The cluster voltmeter will read 0.3 volts low due to voltage drop across the ignition switch contacts. If you have a heavy electrical load at idle, the alternator cannot generate its rated output current and the battery will supply the load current causing a drop in voltage.
The voltage should go to 13.3-14.3 when you get underway and since you don't spend much time idling, don't worry about low voltage. My 87 stays at 13.3 hot to 14.3 cold even at idle. If you have too low an idle speed, you might see the fluctuations you observe.
The voltage should go to 13.3-14.3 when you get underway and since you don't spend much time idling, don't worry about low voltage. My 87 stays at 13.3 hot to 14.3 cold even at idle. If you have too low an idle speed, you might see the fluctuations you observe.
Melting Slicks
Joined: Dec 2004
Posts: 2,954
Likes: 2
From: Obama=death for America
The numbers you're reading are fine. When you start to get in the 11's, then there's most likely a problem. If you have your lights on and the A/C, maybe the wipers, radio and amp., you could see 11's and still you might not have a problem because as soon as you accelerated, your voltage would immediately increase. If it didn't, that's indicative of a problem. If no accessories were on and you see 11's, that indicates a potential problem.
But what you're seeing is normal, so faw git abowt eet.
But what you're seeing is normal, so faw git abowt eet.
Thread Starter
Intermediate
Joined: Mar 2003
Posts: 31
Likes: 0
From: Irvine ca
While driving it shows maybe 13.2 to 13.5 most times. My idle is in the 550 to 600 range. The reason that I thought the ECM might be altering the idle speed attempting to adjust the alternator's output to adjust for load.
