Alternator not charging

[Eich]

Hey guys and gals.

I just got back to town yesterday after a few months overseas. While i was gone the battery went dead. Dad went and put a new battery in it, but hooked up the cables wrong. He said he did crank it twice with the cables on wrong. (yeah i know they are 2 diff sizes oh well)

The jeep is a 91 xj.

Some of my accessory fuses were blow (CB radio etc.) i replaced them.


So I put a new battery in it, starts and runs fine. But the volt meter on the dash is showing roughly 10 volts. I put a new alternator in it, and the problem is still there. I checked the fuse behind the battery where the relays are (60 amp) for the alternator it didn't pop and still has voltage running through it.

I just checked the ends of the wires from the alternator to the battery, and didn't notice any fusible link, but haven't opened up the wire bundles to check and see if there are any in-line.

The readout on the dash shows it at 10 volts still.

I did a search for fusible link, but all the ones listed with my type of problem are all older non HO engines. So I'm assuming that mine doesn't have a fusible link due to it having the 60 amp fuse..... But thought id ask and see if anyone knows.

So any ideas of what i should check next?
Anyone know if there is a fusible link on a 91? If so where?

Thanks in advance for the help.

 

[old_man]

Put a voltmeter on the battery and see what it really is first. If it is 10v, then the battery either has a shorted cell, or the alternation is shot. Remove the battery cables and measure the battery, if it is still 10v, then definately bad battery.

 

[5-90]

Yechh. A big issue here is that 91-up alternators were externally regulated, which means that you haven't replaced the regulator (and I hope it's not popped, since it's in the ECM!)

There's not much to the 1991 XJ charging setup - let me peruse my 1991 FSM...

OK, the alternator output goes from the screwpost on the back of the thing, splits in two, and goes into the PDC (no, I'm not sure why they did it that way either. Seems silly.) For the other three wires down there...

The black one is the ground - it goes to the engine block right next to the alternator. Not much to go wrong there.

The Grey one goes up to a 10-way connector near the battery, and thence (but changing colour to Dark Green/Orange tracer) a splice that eventually goes to ECP pin 57 - Auto ShutDown (ASD) sense.

The Dark Green wire with the Red tracer goes to the same connector, turns to plain Dark Green (no tracer,) and goes to ECU Pin 20 - Alternator Output (this is the one that supplies the Field voltage to the alternator. THIS is the one you'll want to check with a voltmeter - while the voltage here is quite low (should be something like 1-4 volts,) you should be getting something. If there's no field supply voltage, there's no alternator output.

Since your XJ starts and runs fine, it's possible that if the regulator's blown, that's the only part of it that's shot. It may be possible to source a "one-wire" replacement that is self-exciting (converts to an internal regulator with an internal sense lead) and that will reduce the cost of the repair. See what you can find out, and I've got to go talk to my electric shop on Monday anyhow - I can see if he can come up with something for you.

5-90

Oh - there are no fuzible links. The alternator power gets to the PDC BUSS bar via Fuzes F8 and F16 - both are 60A MAXI fuzes. You might want to check those as well - I nearly forgot.

5-90

 

[Eich]

5-90 thanks for the very detailed repy.

I was afraid it was going to be a pcm. darn.......

Well ill monkey with it a bit tomorrow and see if i can run all the wires just for the heck of it, to make sure that it didnt scorch one of them when he hooked it up wrong.

Ill post what i find.

----
Old man
I did put a volt meter on it, altenator is not charing, I tested the battery its at 12.5 volts.

 

[5-90]

Would you like me to see if there's a one-wire option on Monday? Let me know, so I'll remember to ask while I'm there. I'm reasonably sure it's possible - you'd be amazed at some of the conversions I've seen.

It's really too bad ChryCo went to the Denso rather than keeping the Delco - it's so much easier to work with.

5-90

 

[Eich]

Would you like me to see if there's a one-wire option on Monday?
5-90

No dont sweat it man. I think i got a PCM coverd for under $100, that i can try before I buy. Just got ahold of my guy after i made my last post.(Its good to be drinking buddies with the manager of autozone)

Ill report back on monday once i try it out.

Thanks again

 

[Dingo509]

Would you like me to see if there's a one-wire option on Monday? Let me know, so I'll remember to ask while I'm there. I'm reasonably sure it's possible - you'd be amazed at some of the conversions I've seen.

5-90

I'd like to know if there's a one wire available, or at least a way to bypass the regulator in the computer. I've only ever been able to get around 13.2-13.5 out of mine. So i want to install a external adjustable regulator. But im not sure if it will screw with the computer too much or not.

Dingo

 

[5-90]

I'll ask him to-morrow. If I find anything out, I'll post it at WIP - so check it out there.

5-90

 

[e-vasko]

5-90

Thanks for the tip on the 60A Maxi fuses.

I just added a '92 MJ to my fleet, and being old school on alternators, when it didn't work I assumed (yes I know) that the regulator was bad and built into the alternator. I now have a nice new alternator, a spare on the shelf and two new 60A fuses. Lesson learned!