1995 JEEP GRAND CHEROKEE BATTERY DISCHSRGE

  • Tiny
  • morrie46
  • 1995 Jeep Grand Cherokee
  • 196,000 miles

I have a 1995 Jeep grand Cherokee with a 4.0 litre engine. The ammeter shows a discharge whenever the engine is running, have had the battery and alternator checked, both are fine. My thought is voltage regulator, I don, t know how to find it or if I can replace it myself. Someone said it was in the ECM, which may mean replacing that item. Can I do that myself? Any quirks to watch fro, any reprograming? Please help

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Tuesday, June 18th, 2013 AT 10:47 AM

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  • Tiny
  • caradiodoc
  • Expert
  • 25,451 posts

Yup, the voltage regulator is in the Engine Computer and it causes very little trouble.

How could the alternator test fine if the voltage regulator is suspected of not working? Start by measuring the battery voltage while the engine is running. It must be between 13.75 and 14.75 volts. If it is low, measure the voltages on the three wires on the back of the alternator while the engine is running, and holler back with those numbers. The large output wire and one small wire must have full battery voltage. The second small wire must have less but not 0 volts.

I have to run out of town to help a friend in his body shop. I'll check back as soon as I get home tonight.

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Tuesday, June 18th, 2013 AT 11:13 AM
  • Tiny
  • morrie46
  • Member

I just got your message and it is dark so I will check first thing in the morning and get back to you. Thank you.

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Tuesday, June 18th, 2013 AT 7:02 PM
  • Tiny
  • morrie46
  • Member

I started the Jeep, chcked voltages, they were as follows:
Battery- 14.34V
Alternator- 2 leads- 14.22V
Alternator- 1lead- 10.22V
Yesterday, after shutiing it off, it would not start, hardly rolled over until it would not even do that. Perhaps I have a starter problem rather than a charging problem. Left over night, went out this morning and it started immediately.

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Wednesday, June 19th, 2013 AT 8:29 AM
  • Tiny
  • caradiodoc
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  • 25,451 posts

The charging system is working perfectly. The question is why the ammeter is reading so low. 14.34 volts at the battery is perfect. It's normal for one small wire on the alternator to read a tenth of a volt lower due to the losses in the wires and automatic shutdown relay contacts. 10.22 volts on the control wire is also just fine. The lower that voltage is, the harder the alternator is working. The difference of 4.00 volts is what is creating the electromagnet that's needed to generate output current.

For intermittent slow cranking, you may want to measure the voltage right at the starter on the fatter battery cable while a helper cranks the engine. The industry standard is it should go no lower than 9.6 volts. If it does you either have bad bushings in the starter and the armature is dragging or there's a bad connection or numerous frayed strands of wire on the cable, sometimes hidden under the insulation.

If you find the voltage at the starter is okay, or even a little higher than normal, say around 11.0 volts, there may be one open pair of brushes in the starter motor. That will cause it to draw half the normal current at first. Without going into lots of electrical theory, current flow will be correct and normal, but the strength of the motor will be half of normal. Typically the worn brush will make contact once the armature starts to spin, then the cranking speed will be back to normal, but as that brush continues to wear, the slow cranking will appear more frequently.

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Thursday, June 20th, 2013 AT 1:33 AM
  • Tiny
  • morrie46
  • Member

Thank you for your response, that is exactly what has been happening. I will check it out and let you know. Morrie

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Wednesday, June 26th, 2013 AT 6:25 PM

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