First thing you need to do is examine the battery and make sure it passes a voltage and load test. Hold off on any alternator testing until you do the following:
Be absolutely sure the battery terminals are clean where they mate with the battery posts. Examine the terminals really well to be sure they are in good condition. If you have a fully charged battery, place a voltmeter terminal (probe) on the (++) lead post and the other voltmeter probe on the metal portion of the battery wire terminal itself. In other words, the voltmeter probes will be about 1 inch apart. One touching the lead post, one touching the terminal metal. Disable the ignition by disconnecting the ignition coil (should be on top of the valve cover.) Crank the engine for about 2 seconds and monitor any voltage fluctuation on the meter. Anything more than 1 volt: Go back to cleaning or get new terminals. For the Neg (--) terminal, do the same thing, but go from the Neg Batt lead terminal to the engine block.
Now that we've ruled out the battery and posts, do another voltage test on the alternator, engine running. Be aware, though, there are two types of alternators, and they are not interchangeable. One type has three wires on the larger quick disconnect. This type of alternator puts out a continuous 14.5 volts. If your alternator is "bad", aftermarket alternators will work fine.
The other type of alternator has 4 wires at the quick disconnect. This type of alternator has its output controlled by the Body Control Module. Voltages may range from 12.5 volts to 14.5 volts, depending on vehicle electrical requirements. Run the engine, turn on all accessories, Air Conditioning at full blast, brake lights, high beams, etc... If voltage falls below 12.3 or 12.4 volts at idle, replace alternator.
Word of advice: 4-wire alternator?? Go with Motorcraft unless you want to practice your alternator replacement skills a few times. Aftermarket 4-wire alternators just don't work well unless you get lucky. (I can speak from personal experience.... replaced 4-wire alternator with 3 different units from 3 different stores. Then I went with Motorcraft and ..........bingo!!
Alternator charging.
Dec 21, 2008 at 10:39 AM
