Hi all -
This has baffled me - but I hope someone can shed some light.
I replaced the alternator in my '00 Windstar LX 3.8 late last year to solve a low-voltage charging problem - but the problem still appears intermittently. Here's the pattern I've noticed:
- If I start the van in the morning after sitting all night, charging voltage is about 14.1 V (measured with a quality digital multimeter), and stays consistent as I drive. This is correct behavior.
- If I turn off the van when warm - and restart a short time later, charging voltage is now stuck at about 13.3 to 13.5 volts, and will not climb back to full voltage. If my wife runs a series of errands during the day, the battery will become discharged to the point that my benchtop battery charger initially pushes 6-8 amps to bring it back up to full voltage that evening. If I don't charge it manually every day or so, she'll end up needing a jump in just a few days.
At first, I was sure I was the victim of a set of bad alternator regulators. After 3 alternators (that's another story), I'm convinced the alternator itself is fine (and I can now swap Windstar alternators in under 15 minutes).
I also tried swapping out the battery with another vehicle - just to make sure a bad cell or something similar wasn't causing problems. I see the same symptoms.
I've cleaned, tightened and checked ground terminals, battery terminals and alternator connections. I've measured the voltage drop and resistance across major cables between the alternator, battery and chassis ground. In general, voltage drops are under 0.15 V - which is fine based on what I've read. Comparable resistances are no more than 1 to 2 ohms (it's difficult to get good low-resistance readings on these cables). I was also suspicious of the fusible links in the wiring harness - but they check out OK.
I now suspect either a problem that affects the +12V ignition supply to the alternator (not the field supply line - which is direct to the battery through a fusible link and checks out OK). Could it be a marginal relay that works when cold - but doesn't completely close when warm? Could it be a wiring harness problem that's affected by vehicle movement and difficult to track down? I'm not sure.
I appreciate any guidance from the Windstar community!