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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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1998 Crown Vic, Handling and Performance Package

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#4100160 - 03/02/21 09:15 PM Re: Battery discharging while driving [Re: baerster]
85GT Online   content
Member

Registered: 10/30/13
Posts: 392
Loc: NYC
Sure sounds like your alternator is kaput. Unplug anything from it?
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85 Mustang GT w/4R70W
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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: 3150
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 Offline

Poobah

Registered: 11/30/01
Posts: 9441
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: 7513
Loc: MA
Beg/borrow/steal a voltmeter and check the battery terminals with the engine running...should be around 14V.
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'00 Grand Marquis GS (Silver)
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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: 625
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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97 CVPI, 142K miles, small trans fluid leak from front seal area, water leaks to inside from evaporator housing and drivers side A pillar, cold weather glitch with wiper motor, headliner covering starting to flake off, tear in drivers seat bottom. Flickering, blinking radio display, What's next?

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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: 36
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: 3319
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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#4106434 - 04/26/21 07:17 PM Re: Battery discharging while driving [Re: baerster]
Dmblanch Offline
Member

Registered: 11/13/19
Posts: 230
Loc: Utah
I just had pretty much the same thing happen to me in one of my cars. Battery seems to lose charge while sitting for more than a week, or now while driving. It accepts an overnight trickle charge quite nicely and on my Foxwell battery tester, it says "good battery", but here's what happened two days ago.

My nephew started the car in the morning, drove it to my office to deliver something to me, parked it, started it 9again, and drove home (about 20 blocks). Then 20 minutes later, it would not start again for him. I got home, and put my battery tester on it, it read "Good battery-recharge, 11.2 volts, state of health 65%, state of charge 5%". It had started twice a half hour before, and now it's out of charge.

So I put it on the trickle charger overnight, it measured "Good battery, 12.7 volts, state of health 78%, state of charge 100%". I let it sit another night again, unused, and the next morning it read same volts, good battery SOH 73%, SOC 95%. So it was dropping while sitting. Parasitic drain? I dunno, I'm all confused now because it always starts again after a jump and the voltmeter always reads 14 volts while running.

I drove it this morning 4 blocks to O'Reilly's because that's where I bought the battery from less than 3 years ago. I Tested it again with my Foxwell, still said good battery but SOH was now down to about 50% and SOC was like 65%. In four blocks of driving.

O'Reilly's more sophisticated tester instantly said my battery was bad, but my alternator was fine. So I swapped the battery under-warranty.

What did I learn from all this? My Foxwell battery tester is worthless garbage, and so was my SuperStart battery.

In fact, I wonder really if any new battery is any good. They just don't last anymore, I don't care where you get them. Used to be a battery would last 5 to 10 years. Now you can barely get 3.


Edited by Dmblanch (04/26/21 07:21 PM)
_________________________
1) 2002 White P71 - UT Training vehicle w/bad paint, 89K miles, sold.
2) 2003 B&W P71 - UT Patrol car w/bad paint, 74K miles, sold.
3) 2005 White P71 - immaculate WA Fire Chief vehicle, 54K miles, bought w/siren & lights intact, sold.
4) 2011 Black P7B - CA Sheriff vehicle, 79K miles, rented as a movie prop, sold.
5) 2008 White P71 - Idaho sheriff vehicle, 95k miles, outfitted as movie prop rental.
6) 2005 White P71 - UT University police, 74k miles, sold.
7) 2004 Silver P71 - UT Fire Dept., 104K miles, sold.
8) 2004 Toreador Red LX Sport - Want ad find, 111K.
9) 2010 White P7B SAP - UT Police, 106K, sold.
10) 2010 White P7B SAP - UT Police, 104K, sister to #9, sold.

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#4106446 - 04/26/21 09:11 PM Re: Battery discharging while driving [Re: baerster]
ironmarinebill64 Offline
n00b

Registered: 01/30/21
Posts: 16
Loc: New York, USA
I agree with the other folks posting here: alternator is failing.

If the alternator is working okay, a voltmeter on the battery should read between 13.6 and 14.5 at idle, depending on battery condition and draw.

I know everyone here has different levels of recourses available depending on circumstances, but if there's a decent pick-n-pull or salvage yard in your area, I'd suggest seeing if you can find a working used alternator, which, depending on area might be for less than $50 (The yards in my area always seem to sell the 4Gs pretty cheap).

Along that line, if you can get a decent spare to keep you on the road, rebuilding the old one, as far as new bearings and regulator/brushes can be done on a workbench with minimal hand tools.

I've seen a couple good instructional videos on YouTube, and places like Maniac Motors in Dallas Texas have inexpensive rebuild kits that work well.

If the slip ring is well worn, there's a little more involved, and some soldering will be required

Good luck brother
_________________________
2005 Lincoln Town Car Signature Limited
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1999 Mercury Grand Marquis (gave that to youngest son, and he's now a converted true believer)

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#4106560 - 04/27/21 03:43 PM Re: Battery discharging while driving [Re: baerster]
RipWixomAssembly Offline
Rookie

Registered: 01/28/20
Posts: 62
Loc: Michigan
I also agree with it being the alternator.
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RIP Wixom Assembly 1957-2012 CVN Discord
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#4108556 - 05/11/21 02:28 AM Re: Battery discharging while driving [Re: baerster]
Dmblanch Offline
Member

Registered: 11/13/19
Posts: 230
Loc: Utah
Just lost my second O'Reilly Superstart 650 CCA battery in 2 weeks. This one was exactly 3 years old, so no warranty replacement. Replaced it with a Walmart Neverstart 750 CCA at $69, per the Scotty Kilmer recommendation. We'll see how long it holds
_________________________
1) 2002 White P71 - UT Training vehicle w/bad paint, 89K miles, sold.
2) 2003 B&W P71 - UT Patrol car w/bad paint, 74K miles, sold.
3) 2005 White P71 - immaculate WA Fire Chief vehicle, 54K miles, bought w/siren & lights intact, sold.
4) 2011 Black P7B - CA Sheriff vehicle, 79K miles, rented as a movie prop, sold.
5) 2008 White P71 - Idaho sheriff vehicle, 95k miles, outfitted as movie prop rental.
6) 2005 White P71 - UT University police, 74k miles, sold.
7) 2004 Silver P71 - UT Fire Dept., 104K miles, sold.
8) 2004 Toreador Red LX Sport - Want ad find, 111K.
9) 2010 White P7B SAP - UT Police, 106K, sold.
10) 2010 White P7B SAP - UT Police, 104K, sister to #9, sold.

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#4108670 - 05/11/21 07:40 PM Re: Battery discharging while driving [Re: baerster]
MurkyMerc Offline
n00b

Registered: 01/06/15
Posts: 36
Loc: NH
I'd have the entire charging system analyzed particularly the alternator. The battery should not discharge like that.

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