Question99 Deville
When at idle with the brake on, from the digital dash can see the voltage drop at a steady rate from a normal 13.8-14.2 VDC down to 12.5-12.3 VDC or so. At that point the engine will stumble - i.e. go down to about 450 RPM, Rev up to 800 RPM and settle back at 650 RPM or so. This will happen every couple of minutes if continue to stay at idle with the brakes on (or in stop and go traffic).
Also, while while driving (at any speed including up to 65 MPH) the lights will dim and go back to normal at a rate of a few times a second. Sometime will do this even when the voltage readout appears to be steady - sometimes it is associated with a noticable drop in displayed voltage.
Battery seemed OK - started at cold temps and such. Checked the battery. Failed a load test. Put in a new one - no improvement.
Don't have any check engine lights. Have not checked codes. I see that the alt on this thing connects to a Power Control Module (PCM). Seems like something is telling the alt to turn off every once in a while - pretty obvious for the stumble at idle. Not sure what would make the lights flicker when the voltage appears to be OK.
AnswerThe first thing you need to do is give the new battery a chance to get fully charged as when they are new they are only partially charged and it takes a few days of driving to fully charge the battery.
next would be a fault within the alternator which needs to be LOAD TEASTED by a repair facility.
Third would be a problem with the PCM (computer).
Is or HAS the check engine light ever illuminated on the dash while driving the vehicl;e and if it HAS, You need to see what codes are being stored in the computer.
You also want to make sure that your battery cables are not corroded and or loose at the battery, starter and on the ground source of the engine.
