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#4100152 - 03/02/21 08:23 PM Battery discharging while driving
baerster Offline
Rookie

Registered: 07/16/17
Posts: 76
Loc: WA
Hello,

The battery on my 1998 LX discharges while I am driving, until my dash goes dark (lights all go out), engine starts running rough, and then eventually the engine dies. Re-charging the battery overnight with an external charger brings the car back to life for a few hours. It seems that when battery voltage gets too low, the car's electronics including the ECU go haywire and engine doesn't run right under those conditions.

I replaced the battery and that helped for a few days, then the problem came back. A local auto parts store tested the battery, alternator, and voltage regulator and all tested fine. Any advice on how to track this down, or on what this is?


Edited by baerster (03/02/21 08:24 PM)
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#4100160 - 03/02/21 09:15 PM Re: Battery discharging while driving [Re: baerster]
85GT Offline
Member

Registered: 10/30/13
Posts: 388
Loc: NYC
Sure sounds like your alternator is kaput. Unplug anything from it?
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#4100166 - 03/02/21 10:19 PM Re: Battery discharging while driving [Re: baerster]
2007CrownVic Offline
Over the Hill

Registered: 11/19/11
Posts: 3135
Loc: Canada
That's my first thought too. It's not charging properly and only running off the battery.

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#4100174 - 03/02/21 10:58 PM Re: Battery discharging while driving [Re: baerster]
Bangster Online   content

Poobah

Registered: 11/30/01
Posts: 9404
Loc: Tucson Az
Does the battery light on the dash illuminate during the bulb test (in run but not yet started)? How about come on before the car dies with a dead battery?

How was the alternator tested, you removed it and they put it in the machine, or tested it in place?
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#4100176 - 03/02/21 11:08 PM Re: Battery discharging while driving [Re: baerster]
RF_Overlord Offline

Poobah

Registered: 12/14/02
Posts: 7476
Loc: MA
Beg/borrow/steal a voltmeter and check the battery terminals with the engine running...should be around 14V.
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#4100178 - 03/03/21 12:49 AM Re: Battery discharging while driving [Re: baerster]
Rootintootin Offline
Climber

Registered: 02/26/08
Posts: 621
Loc: North Carolina
+3 on the alternator.

Go to another local auto parts store. Nothing says you can't get a second opinion. People do that all the time.

You can buy a cheap but functional voltmeter for less $10. HF used to have one they would give you free when you bought something else. I don't see how anybody could do their own work without one. The first time you fix an electrical problem on your own will pay for it or even a good, more expensive one.
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#4100192 - 03/03/21 10:55 AM Re: Battery discharging while driving [Re: baerster]
MurkyMerc Offline
n00b

Registered: 01/06/15
Posts: 34
Loc: NH
Now you need to grab a DVOM and perform voltage drop tests from battery to altnernator,to engine block and chassis grounds,parasitic drain test on negative side-should have less than 75 milliamps,and running load test on the alternator- should be >9.6v for 10 seconds.All this can be done with that meter.Will tell you a lot.


Edited by MurkyMerc (03/03/21 12:14 PM)

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#4100204 - 03/03/21 01:34 PM Re: Battery discharging while driving [Re: baerster]
CrystalPistol Offline

Over the Hill

Registered: 10/16/01
Posts: 3035
Loc: Shenandoah Valley
Originally Posted By baerster
Hello,

The battery on my 1998 LX discharges while I am driving, until my dash goes dark (lights all go out), engine starts running rough, and then eventually the engine dies. Re-charging the battery overnight with an external charger brings the car back to life for a few hours. It seems that when battery voltage gets too low, the car's electronics including the ECU go haywire and engine doesn't run right under those conditions.

I replaced the battery and that helped for a few days, then the problem came back. A local auto parts store tested the battery, alternator, and voltage regulator and all tested fine. Any advice on how to track this down, or on what this is?
Sounds like Alternator going away or gone.
The battery is a storage device, when it gets used up without the alternator putting energy back, electronics start fading, car dies. Batteries like to stay charged, repeated full discharges of a car battery will shorten it's life.

I know we (Advance Auto Parts) have a hand carried tester to take into the parking lot, it works well ... but we also have a test stand for alternators, starters, generators. The stand has drawers with electrical adapters to hook up with. Before testing, you enter info for the vehicle and it prompts one to use certain adaptors, etc. It has a sliding carriage and belt to spin the alternators or generators. I worked there after retiring up until '16, then I had to give it up, but they are still close. I'm sure Auto Zone or O'Reilly's or NAPA or Pep Boys all have similar, etc.... free too.

I know some like to unhook a battery to see if a car dies or runs as a test, but don't do that. You can wreck a sensitive electronic voltage regulator that is usually built into that alternator these days.

If me, if I were exactly in your shoes, I'd take a breaker bar that fits the belt tensioner square and a 10mm wrench and a 10mm socket and ratchet and drive my '98 Panther to the store and take the alternator off and into the store and test it again. It's not so hard if you plan for it, pretty quick too. Take an 8mm to loosen and remove the battery cables from the battery first.

Back in 2005, I got a call to a deer wreck just as I pulled into the parking lot at our area office ... I had a good battery in my '00 CVPI work car, it had been on charge all day too & I had a spare in the trunk ... but I needed a new alternator and had called the Sgt that day before I went to sleep, he had one and a battery relayed up from headquarters during the day while I was asleep and they were in the supply shed, so I swapped the new ones on while in the dark holding a flashlight that cool night in the parking lot under a D-D light too ... then I went and worked my deer wreck. Deer was there and still warm, no one asked what took me so long. I didn't think I needed a new battery, that was Sgt's idea I guess.

(My '00's charging system went on the fritz the night before at the end of my 8 hrs, battery was near dead when I got home at 6am, I could hear enough in the two way to know the diodes were shot, voltage while running was low too ... had it happened earlier in the night I would have needed a tow truck ... but I had an extra Motorcraft Gp 65 battery from my '01 Mercury that I had just replaced for a trip out west, the battery was good but I was planning a long trip so I had just replaced it on account. That Motorcraft Gp 65 is still in a wooden cart that I use for emergency or temporary power, I put a maintainer on it occasionally, never let it go down, little eye is still green here in 2021.)
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#4100610 - 03/05/21 03:05 PM Re: Battery discharging while driving [Re: CrystalPistol]
baerster Offline
Rookie

Registered: 07/16/17
Posts: 76
Loc: WA
Thanks for the replies! I will get the alternator tested for real, I like the suggestion to bring tools with me to the auto parts store to take it out of my car, have it tested on a stand. Thanks!
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