Charging issues

So the check engine light on my XJ has been coming on (as well as the volt meter on the instrument cluster has been reading low voltage) since the cold weather began and I have pulled a code 41 (alternator field not switching).

Last night I tightend the battery connections, cleaned the corrosion at the alternator connectors, cleared the code and on initial start up the light went out and the voltage was reading better than 14.5 volts. This morning when I went to start the Jeep the light came back on and the voltage was reading low. If I wiggle the wires at the alternator, the light goes out and the voltage comes up. I double checked all the connections and they are tight.

So my question is, do I have a bad alternator or is the wire/connector going to the field switch on the alternator NFG? If its the wire/connector, can it be replaced, or is it part of the harness that goes to the PCM?

Any info would be greatly appreciated.

Thanks, and Merry Christmas!

I'd check the crimp at the connector, next maybe the wire under the insulation may have fatigued from vibration and is down to a few strands of the original wire under the insulation. You can often feel this through the insulation with your finger tip or finger nail or while gently kinking the wire.
The path is from the ASD relay to the alternator and should be near battery voltage and then from the alternator to the regulator in the PCM, which actually regulates (or switches) the amount of voltage on the ground side of the system.
With the connectors connected and the otor running, If you hook up a volt meter to the field "in wire" dark green with and orange stripe if I remember correctly and the field "out wire", you can measure the voltage drop across the alternator field windings and watch the PCM regulate.

So I went and checked the rest of the connections (ground cable at fender, ground cable at firewall, etc) and still getting the same problem. I decided to give the alternator a smack with a BFH, lo and behold Check Engine light is out and the voltage on the gauge is reading where it should be. Looks like the alternator is NFG.

My truck has the 90 amp alternator and so my next couple of questions are...Has anyone ever taken one of these units into a shop and had it rebuild to crank out a few more amps? And if so how much more was the shop able to provide?

Thanks!

'95XJ said:

My truck has the 90 amp alternator and so my next couple of questions are...Has anyone ever taken one of these units into a shop and had it rebuild to crank out a few more amps? And if so how much more was the shop able to provide?

Thanks!

Click to expand...

the bearing in my old 90 amp alt went out on my 95 xj. i decided that it was time to upgrade rather than just replace. i went with a 136 amp alt from a zj. there have been numberous threads on this issue and searching will yield lots of results.

it wasnt quite a direct swap. the brackets that attatch it to the engine had to be ground down with a dremel slightly. also the plastic piece that surounds one of the connections had to be swapped out with your old stock one. the pulley on it has an extra groove on it (zj belt is a wider by one groove). just ground the serp belt to the rear and you will be good. or you could pull the pully from your old one.

i dug around a little bit and found one of the links i used.
http://www.bc4x4.com/tech/2004/jeepalt/

hth
stewie