Charging System Failure

[BruceDavis]

After installing a NAPA rebuilt alternator and a new battery the charging system on my '92 W250 still fails to provide any charge. By jumpering a ground to the (-) alternator field terminal and also by-passing the auto-shutdown-relay with a jumper from the (+) side of the battery to the (+) alternator field terminal I can get 15V output from the charging system. Now the question is: What is preventing the charging system to work properly?



Is it a bad auto-shutdown-relay?



Is it a bad engine control module (black box)?



What else could it be?



Bruce Davis

Long Beach, CA

 

[Leper]

The pcm is probably bad for the charging circuit. Common problem. You can replace the pcm, or you can add an external regulator from an older model.

FAQ

link

 

[JGrefenstette]

bruce,

hate to have to tell you this. but i had the exact same thing with mine. seems not that uncommon for these old trucks to have it happen. i replaced my alternator and charged the battery. it turned out to be the PCM. i got it for $130 after the core. not to bad. easy to install.



But, are you testing the battery from the terminals, or watching the dash meter. because those dash gauges can be incorect. ive heard from many that they dont read properly. mine will read around the left for a while when im driving the ill hear a little pop and itll jump to the right. just old gauges that probly wernt that good to start with. gotta love dodge

 

[Niki]

A bad or improperly adjusted crank sensor will also tell the computer that the motor is not turning, so no charge.

 

[BruceDavis]

You hit the nail on the head Niki. I pulled the connector at the crank sensor, tried to snug up the female end a bit and reconnected it. Every thing works great now. It probably was bumped at the dealer.

Bruce

 

[BruceDavis]

The problem turned out to be a loose connection in the crank sensor circuit. Problem solved without $pending more on parts. Thanks for the response.

Bruce