Hey all, I've got a 91 b250 with the 5.2 engine and I'm having a problem with the alternator not charging.

I did the whole 'pull the battery cable while it's running' test, and it killed the engine, so I figure the alternator was bad...but no.

I had it checked while it was in the van at autozone, but it was not sending a charge to the battery. I took it out a bit later, had it tested out of the van, and it passed at multiple stores, so I'm assuming now the alternator is fine and that there's an electrical issue somewhere else.

Everytime I hook the alternator terminals back up and start the van, the battery meter will read the normal 14v, but only for about 3 seconds and then it drops down to 10v and the check engine light kicks on.

I did the key dance thing and got codes 12, 41 and 55.

So yeah, I'm curious if anyone else has had this issue and maybe knows what it could be? Maybe a bad wire somewhere, or the alternator is just going out perhaps?

Thanks for any help on this.

 

Pulling the battery cable with the engine running has been a bad idea for about 40 years now. It can cause electronics burning voltage spikes, or even blow diodes in the alternator.

The voltage regulator is inside the engine computer. Follow the wires between alternator and engine computer and make sure neither is grounded out.

Clean you battery terminals and firewall and engine grounds. Locate and clean or add a frame to engine ground.

There is a fusible link stuffed behind the brake booster. At this age they can corrode from within and only pass current when they feel like it. A hungry battery asks for too much and the fusible link say enough!

They should blow and have burnt looking insulation and stretch out, but often when they are this old it does not work that way.

There are ways to add an external voltage regulator bypassing the one in the engine computer, but everything else should be ruled out first.

 

The code 41 means there is a loss of the alternator field connection. That's the little wire(s) going to the alternator. If the field wiring in the van checks out okay, then you're likely looking at an internal alternator wiring break.