XJ alternator low voltage & stalling. - JeepForum.com
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post #1 of 9 Old 06-08-2021, 09:07 PM Thread Starter
harrygatto
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XJ alternator low voltage & stalling.

My XJ is a 1996 Limited 4.0 litre, JDM (Japan Domestic Market) model which means effectively RHD, UK spec with kph speedo, fully loaded, electric everything and factory build sheet says 117 amp alternator. I live in Japan.
I have had the car a long time, since 1998, so I know its ways and its history, Currently on about 90,000 km or 60,000 miles so pretty low. Usual problems over the years including new starter, water pump and radiator, roof lining falling down.
The voltmeter on the dash at the lower right has marked positions at 9, 14 and 19 volts. The car has always read 14 volts exactly even at idle only dropping around 1 volt when heavy load (e.g. AC and headlights) is applied. However, quite recently and quite suddenly the voltage at idle has dropped to about 10 or 11 volts only increasing to 14 when engine rpm is 1800 or higher. I have double checked these readings with a meter on the battery terminals and they are accurate.
Coupled with this another problem has arisen and that is the engine sometimes will not idle and just cuts out, a real problem if you're in the middle of a junction on a 4 lane road with no brakes and steering juggling everything to get the transmission into neutral so it will start, which it always does. I do not know if these two issues are linked.
I have also noticed that when starting from cold the engine sometimes needs to turn over for a couple of seconds longer before it fires. Also, a couple of times I have noticed what feels like too far advanced ignition timing kicking back the starter. Engine starts on second attempt. This issue is not consistent, maybe 1 in 5 times.
Just before these problems came up I had the AC re-gassed but for the life of me I can't think how that could be related.
Sorry for the long post, I have a good look at everything but all looks OK so any pointers on where to go next would be welcome.

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post #2 of 9 Old 06-08-2021, 09:10 PM
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How’s your battery?

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post #3 of 9 Old 06-09-2021, 02:30 AM Thread Starter
harrygatto
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In good shape, 2 years old, holds charge and spins the motor just like a new car.
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post #4 of 9 Old 06-09-2021, 04:55 AM
CJ7-Tim
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If the voltage gauge shows 9-10 volts the alternator is your primary suspect. Usually the brushes are worn down. If the voltage gauge shows 18-19 volts, the primary suspect is loose, dirty, corroded or damaged battery/alternator connections or cables.

The stalling is most likely a symptom of low battery voltage from poor alternator charging.

Have the battery and the alternator Load Tested. The alternator may pass a load test, be sure to inspect the brushes.
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post #5 of 9 Old 06-09-2021, 09:31 AM Thread Starter
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Will do, very many thanks.
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post #6 of 9 Old 06-11-2021, 10:43 AM
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Also check to be sure that your belt isn't slipping. Recharging the A/C system would have put a bit more load on the belt, and, if it was barely holding on beforehand, cause it to start slipping, which could also explain your issue.

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post #7 of 9 Old 06-11-2021, 10:15 PM
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The low volts in the system is causing the computer to freak out. When it gets below 10 on the volt side it starts going haywire and much lower it will shut down the system. Same if the RPM drops below about 500 at idle. Check the alternator, its plug, wiring and all the grounds in the engine bay.

But the belt being worn and stretched or not having the right tension could be something to look at for sure.

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post #8 of 9 Old 06-12-2021, 10:49 PM Thread Starter
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Thanks to all for the replies. It seems the alternator is faulty and though it may be possible to get it overhauled here, with the Jeep being "foreign" that might be difficult. The dealer is worse than useless and ridiculously expensive. Amazon can supply but with crazy high delivery prices because of the weight and also with Covid international shipping can be difficult at the moment.
However, an imported car parts specialist here (I got a new starter from them a few years ago) tells me they have a new alternator in stock at a reasonable price but it is a 90 amp version instead of the 117 amp version fitted on my car (according to the factory build sheet). Assuming that it is physically the same as mine, connections etc. could I fit it and what are the implications. I only do 2 or 3 thousand miles a year and no night time journeys with AC on. Being RHD the alternator is high up on the right side of the engine, I have attached a pic.
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post #9 of 9 Old Yesterday, 06:42 AM
CJ7-Tim
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The 90 amp alternator is not a direct exchange part, but I think I recall that the metal plate on back can be exchanged and it will then fit and work.

The NipponDenso alternator likely only needs new brushes. Any local experienced automotive electric shop can easily rebuild it.

“We the people are the rightful masters of both Congress and the Courts,
not to overthrow the Constitution but to overthrow the men who would pervert the Constitution” Abraham Lincoln, 1859.
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