Alternator?
Thread Starter
Instructor
Joined: Sep 2007
Posts: 197
Likes: 0
From: Old Tappan New Jersey
Alternator?
While starting the car when turning over i have had some problems recently. It sluggishly starts and the average MPG gets reset, as well as the heads-up display meter (i keep it on gas - it gets reset to temp which is the default). This only happens it in the morning when the car sits all night - throughout the day it starts up ok - but not great. Not the battery because i just replaced that recently. Alternator? Something else? Thanks for the help.
Burning Brakes
Joined: Dec 2003
Posts: 1,066
Likes: 9
From: Eddy Texas
I think all those things reset to default if the battery voltage drops below 10.5 when cranking. If your battery is new I would check the cables and connections. Would'nt be the first new battery that failed either.
Tech Contributor
Joined: Apr 2007
Posts: 10,924
Likes: 78
From: Forney Texas
The best way to test a battery is with a mid-tronics test set. Unfortunately, they cost 4500.00 and few people have them. I would recommend you start the vehicle and measure the voltage across the battery terminals. With the vehicle running, it should be 13.8 or so. Then use your DIC to see the voltage that the computer sees. This will take into account for any wiring issues causing voltage losses. If you see a huge difference, you'll need to begin chasing down your voltage drop. If you don't see 13.8 or so at the battery, test the voltage from the back of the alternator + post to the alternator's chassis. It should be around 14v. If it's not, you have an alternator field charge wiring problem or a defective alternator. If you do get good voltage at the alternator, begin loading it by turning on some accessories such as the A/C, rear defogger, headlights. If the alternator voltage falls below 12.7v, you have a weak alternator. Replace it.
Safety Car
Joined: Dec 2004
Posts: 3,526
Likes: 18
From: Santa Fe TX
I simple cheap load tester will probably do the job as well. Loads up the battery and then has ranges into which the battery voltage falls that read Good(green) ok(yellow) and Bad (red)
It is a box attached to short jumper cable looking wires.
It is a box attached to short jumper cable looking wires.
