windstar check charging system

I got a check charging system light. Checked the output of the alternator and was only getting 11.6v. Replaced alternator 3x and each time only got 11.6v until I revved the motor above 2k rpms, then the alternator output would jump to 13.5v and the check charging system message would momentarily disappear then reappear in about 5 seconds. I put a meter on the 3 wire connector of the alternator. I got battery voltage on the one wire . after starting I got 11.6v on one of the wires and 8.5v on the another. after reving and getting the voltage up to 13.5v the voltage on teh wire with 8.5v drops to .75v and the light comes back on. I checked the fuses and am thinking the only thing left is the electronic control module. any suggestions would be helpful.

I would try the battery.

One of my co-workers just went through a similar issue.....
He had a place to a "in car check" and they told him that it was the alternator. I had loaned him my charger and told him to charge the battery before starting the car with the new alternator.....
They jump started the car....and it ran fine.....re-started.
Then later he went out.....and the car would not start.....he put my charger on the battery....and it blew the charger.
They got a bigger charger.....and it tripped the circuit breaker on it.
He bought a new battery.....and when he removed the plastic cover off the old battery......they could see that it was bloated.....
New battery solved the problem.

It sounds like your battery is not as bad as his was.....I had never heard of one like his...... But your problem sounds just like a bad cell in the battery.

Replaced the battery today, still no difference. Any suggestions would be much appreciated.

Am I missing a diode or a capacitor that is in line with the alternator or could the control module be failing. If so is the control module hard to replace?

Here's a post made by "Lewisnc100" some time ago. Sounds like it may apply to your situation. Can't tell what vintage vehicle you are dealing with so just a guess. Hope you can find the problem in any case.

Quote:
I've seen a lot of posts around battery drain and vehicles not being able to start in the morning. This might have been posted before, but I ran across a technical service bulletin that requires a PCM reprogram for certain Windstars to prevent reduced battery charge. Here is the details, my Windstar had this done and I haven't seen any problems with the battery charge. The other interesting point about this TSB is that it states there will be no owner notification, they are just making it part of the applicable emissions warranty service so if the dealer doesn't tell you about the TSB you won't be notified. Great customer service.
TSB: 00T07 September 2000 PCM - Incorrect calibration strategy
Affected Vehicles: All 1999-2000 model year Windstar vehicles built at the Oakville Assembly Plant from Job#1 through July 25, 2000.
Reason for TSB: Some of the affected vehicles were built with a PCM calibration strategy that may cause the vehicle to exhibit reduced battery charging performance.
Special Service Instruction: The vehicle's PCM must be reprogrammed using the Worldwide Diagnostic System or the New Generation Star Tester.