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Jeep Cherokee 1990 - not charging

Noticed today that my voltmeter was well in the red while driving to the store. No problem starting yet but only drove 3 km.

This is on a 1990 Jeep Cherokee 4.0L

Something like this happend some years ago and then I had to get a new alternator. Suspect the same this time, but would like some tips on what to check before ordering a new alternator or having a mechanic check this out.

I have a battery tester and a multimeter at hand. I plan to first check the battery with the tester to see if it works ok with load. Then measure battery volts when the car is not running (should be something like 12V) and when car is running (should be higher, preferably 14.4V).

Of course I will try cleaning battery connections (Optima red top battery, some years old).

Anything else I could check?

regards Odd-Inge Larsen North Norway

Reply to
Odd-Inge Larsen
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Slip-ring brushes wear out on an alternator and are relatively easy to replace, besides being really cheap. Before giving up any alternator for dead I check or replace them. Price in the US is about $5.00, about 4 Euros, then add in shipping. The drive belt could be loose too. It should make a noise if slipping, but sometimes they don't.

If you have a manual and a resistance meter (Ohmmeter) you can figure out where the slip ring brushes are connected and check for connectivity. Infinite resistance means the brushes have worn out. I don't know how many rebuilt or new alternators are sold in the US because these little parts have worn out.

Good luck,

Earle

Reply to
Earle Horton

Jepp, brushes was in my mind to. Had to change brushes on my starter motor just a few months ago and that cured it from not turning. Real cheap and easy fix I must say. Problem I guess is finding out what type of alternator I have. How many amps and so on.

Maybe I could try tapping the alternator lightly to see if the bruses make contact again. If so I could be pretty shure that this is the problem.

Good idea to check drive belt slipping. Will do that.

thanks Odd-Inge

Reply to
Odd-Inge Larsen

I am a bit unsure now. Checked every connection and found no problems there. Cleaned battery connections but they looked ok.

Measured only 11.53 Volts on the battery when car not running. It dropped to

11.23 when car was running. Battery tester showed battery as "weak".

Checked another battery in my tractor and it measured 12.2 Volts not running and battery tester showed "Good".

Voltmeter in car shows some charging, borderline red mark.

Attached a battery charger and it seems to struggle a bit putting some juice into the battery. On its lowest setting the meter shows about 10 amps and that's a bit abnormal. I tried this also with battery disconnected from car but no difference.

The battery in my car is a Sonnak Exide, same technology as Optima. It is maybe 6-8 years old. Battery in my tractor is an Optima red top.

regards Odd-Inge

Reply to
Odd-Inge Larsen

I did charge the battery. Seems ok now. Probably just low due to alternator failing.

Did try to knock on the alternator with a rubber mallet. This probably moved the brushes some and the voltmeter jumped to about 14 volts, its normal position. But it fluctuated a great deal and the interior lights flickered a lot. Revved it up and it was not able to charge anymore. Let off the throttle and it charged again.

My diagnoses: Worn brushes in the alternator. Replace brushes or by new alternator.

Does this seem like a reasonable diagnosis?

regards Odd-Inge

Reply to
Odd-Inge Larsen

Yup, the mallet trick sometimes tells all.

Hopefully you got it before the slip rings got damaged.

I would do one more test just to see if the mallet did something else. I would run a battery booster cable from the battery negative to the alternator case and see if the charging goes stable. If so, the alternator case would have a bad ground that the hit moved slightly. It is a sneaky one, but seems to happen on Jeeps a lot.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > I did charge the battery. Seems ok now. Probably just low due to alternator > failing.
Reply to
Mike Romain

Tried the cable trick. Made no difference. As it is difficult to get new brushes where I live and the label on the alternator can not be read without removing alternator I ordered a new alternator. Also one could never know if anything else was damaged inside.

Dealer wanted nkr 4041,- for the original part and it had to be shipped from Germany. Found a new 100A (in stock) at a store located at the norwegian Amcar club for nkr 1763,- included VAT and shipping. (aprox US$ 271)

Hope to have it fixed later this week if all goes well. Thanks for the help guys.

Odd-Inge

Reply to
Odd-Inge Larsen

Make sure the exciter wire has a good connection, it's the small one going to the alt.......Have a good day

Reply to
JRK58

Have now changed alternator. Bits was falling out of the old one when I took it out. Something had smashed the internal cooling fan blades. The new one is working fine. Charging around 14 volts again :-) And much more quiet.

Odd-Inge

Reply to
Odd-Inge Larsen

Thanks for the follow up!

Mike

Odd-> Have now changed alternator. Bits was falling out of the old one when I took

Reply to
Mike Romain

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