[Matthew]

With a brand new battery (not to say that a brand new battery can’t be bad, I’ve seen much to prove that possibility out on the interwebs) while having all accessories turned on with the engine running, I’m seeing a progressive decrease in the battery voltage that is trending towards the key-off voltage.

Not wanting to wreck a potentially “good” new battery, I haven’t allowed the car to run long enough to see if the battery voltage indeed hits the 12V mark.

So, if my key-off voltage is 12.5v, and the load test hits 13v, we’re right at that 0.5v threshold between a ‘properly charging’ system and one that is suspect, correct?

I’ll be going over the wiring with my multimeter and a gimlet eye this weekend this week/coming weekend. Thanks for your help.

PS: I wasn’t trying to be argumentative. I’ve been through hell with this Jeep, and I really miss the days when it “just worked” I could trust it. Random stalling at idle, WOT, or anywhere in between, “two screw” miracle PCM fix, just to name a couple of issues were why it’s been “on ice” for the last two years, while I had neither the time, money, or impetus to try to get it back on the road. This thing is about as cursed as the HT4100 was in my ’84 Seville!

[Matthew]

With a brand new battery (not to say that a brand new battery can’t be bad, I’ve seen much to prove that possibility out on the interwebs) while having all accessories turned on with the engine running, I’m seeing a progressive decrease in the battery voltage that is trending towards the key-off voltage.

Not wanting to wreck a potentially “good” new battery, I haven’t allowed the car to run long enough to see if the battery voltage indeed hits the 12V mark.

So, if my key-off voltage is 12.5v, and the load test hits 13v, we’re right at that 0.5v threshold between a ‘properly charging’ system and one that is suspect, correct?

I’ll be going over the wiring with my multimeter and a gimlet eye this weekend this week/coming weekend. Thanks for your help.

PS: I wasn’t trying to be argumentative. I’ve been through hell with this Jeep, and I really miss the days when it “just worked” I could trust it. Random stalling at idle, WOT, or anywhere in between, “two screw” miracle PCM fix, just to name a couple of issues were why it’s been “on ice” for the last two years, while I had neither the time, money, or impetus to try to get it back on the road. This thing is about as cursed as the HT4100 was in my ’84 Seville!

[Matthew]

Thanks Eric,
I haven’t found the nerve to let it run down that far, but even while holding the rpms higher than idle, I still observed drain in the battery.

Seems to me that sitting in stop and go traffic on a cold/hot rainy day for half an hour would conceivably drop it that far… So I’m reasonably apprehensive of that diagnosis.

I wouldn’t expect to observe a steady drain of any kind. intermittent, perhaps, such as when you have an electric cooling fan, but not continuous. Shouldn’t it level out at some point and hold more or less in the same voltage?

note: when I first installed the new battery, after idling the car for 20 min or so (as battery had been disconnected for ~2 years) the standing voltage was about 12.8v, after letting it sit for a day and then doing a load test on the alt, it was at 12.6v, next day load test for another 20 min, standing voltage is at ~12.3v.

[Matthew]

Thanks Eric,
I haven’t found the nerve to let it run down that far, but even while holding the rpms higher than idle, I still observed drain in the battery.

Seems to me that sitting in stop and go traffic on a cold/hot rainy day for half an hour would conceivably drop it that far… So I’m reasonably apprehensive of that diagnosis.

I wouldn’t expect to observe a steady drain of any kind. intermittent, perhaps, such as when you have an electric cooling fan, but not continuous. Shouldn’t it level out at some point and hold more or less in the same voltage?

note: when I first installed the new battery, after idling the car for 20 min or so (as battery had been disconnected for ~2 years) the standing voltage was about 12.8v, after letting it sit for a day and then doing a load test on the alt, it was at 12.6v, next day load test for another 20 min, standing voltage is at ~12.3v.

[Matthew]

First of all, thanks for the quick replies, everyone.

During the course of troubleshooting this car I did a parasitic drain test, but after the ECU goes to sleep (30 sec or so), drain is only 0.029A or less.

Volt drop on neg terminal to alt casing was about 0.08v.
Volt drop on pos terminal to alt output was about 0.2v.

I’m assuming that if I ohm out the wiring, perfect world scenario would be 0 ohm between any of the major connectors. At what point in ohms would you replace a cable?

Cut that in half and its what a 96 Jeep would probably tolerate. From past research it is apparent that jeeps in general are notoriously picky about parts and electrical, and mine has been no exception.

Thanks again
-Matthew

[Matthew]

First of all, thanks for the quick replies, everyone.

During the course of troubleshooting this car I did a parasitic drain test, but after the ECU goes to sleep (30 sec or so), drain is only 0.029A or less.

Volt drop on neg terminal to alt casing was about 0.08v.
Volt drop on pos terminal to alt output was about 0.2v.

I’m assuming that if I ohm out the wiring, perfect world scenario would be 0 ohm between any of the major connectors. At what point in ohms would you replace a cable?

Cut that in half and its what a 96 Jeep would probably tolerate. From past research it is apparent that jeeps in general are notoriously picky about parts and electrical, and mine has been no exception.

Thanks again
-Matthew

[Author]

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