Voltage Drop
11-13-2016, 04:01 PM
#1
Senior Member
Thread Starter
Voltage Drop
1996 4WD 4.0 Auto
When aquired recently PO said battery is weak, needs replacing. Drove it home 200 miles during the day no issues. I have since upgraded the dash to gauges. Test drive at night with lights on shows voltage drop after 10 mins or so. Multimeter shows charge rate of 13.75v and slowly dropping. Most likely bad alternator? I'm going to check grounds tonight.
Thanks.
When aquired recently PO said battery is weak, needs replacing. Drove it home 200 miles during the day no issues. I have since upgraded the dash to gauges. Test drive at night with lights on shows voltage drop after 10 mins or so. Multimeter shows charge rate of 13.75v and slowly dropping. Most likely bad alternator? I'm going to check grounds tonight.
Thanks.
Last edited by ElMartillo; 11-13-2016 at 04:03 PM.
11-13-2016, 04:49 PM
#2
Banned
Join Date: Oct 2016
Posts: 1,553
Likes: 0
Received 4 Likes
on
4 Posts
Year: 2000 and 1998
Model: Cherokee
Engine: 4.0
i would clean batt terminals. if they are changed and have bare wire clamped id clean and tighten.
those clamps we see so much are terrible.
you could have voltage drop at the batt connections.
those clamps we see so much are terrible.
you could have voltage drop at the batt connections.
11-13-2016, 04:55 PM
#3
Banned
Join Date: Oct 2016
Posts: 1,553
Likes: 0
Received 4 Likes
on
4 Posts
Year: 2000 and 1998
Model: Cherokee
Engine: 4.0
i would clean batt terminals. if they are changed and have bare wire clamped id clean and tighten.
those clamps we see so much are terrible.
you could have voltage drop at the batt connections.
those clamps we see so much are terrible.
you could have voltage drop at the batt connections.
11-13-2016, 06:46 PM
#5
Senior Member
Thread Starter
Cleaned the grounds I could get to. Showed 13.99v upon startup. As it warmed up it gradually came down into the high 13.60v range. This was after idling for 15-20 mins with the lights on. Attached the mm leads to the alternator + output and neg lead to the alt case. Showed 13.75v on average.
What does this indicate?
What does this indicate?
11-13-2016, 07:03 PM
#6
Junior Member
Join Date: Jun 2012
Posts: 81
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee
I had a bad battery terminal give me fits until I figured out it was the problem.
If the alt looks original and you're over 200k miles, it's probably due for replacement.
If the alt looks original and you're over 200k miles, it's probably due for replacement.
11-13-2016, 07:16 PM
#7
Junior Member
Join Date: Jun 2012
Posts: 81
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee
Voltage reading with a "fully charged" battery and the engine idling should be ~13.8 to 14.5ish volts depending on the vehicle. 13.6 is a little low, but not alarmingly low, and probably about right. The headlights/tail lights/etc. were probably using 10-15 amps and the alternator is likely only putting out 20ish amps at idle.
The 13.99v reading was likely the alternator upping output(as much as it could) to restore the energy used by the starter. If that reading was taken before starting the vehicle, then it was high due to "surface charge" on the battery.
The 13.99v reading was likely the alternator upping output(as much as it could) to restore the energy used by the starter. If that reading was taken before starting the vehicle, then it was high due to "surface charge" on the battery.
Trending Topics
11-18-2016, 08:15 AM
#8
Senior Member
Thread Starter
I put in a new alternator yesterday. Still low voltage reading. Multimeter on alternator, not at the battery, says 13.30a upon startup, now slowly dropping to 13.06a after idling for 10 mins. No real change from the old alternator.
Drove it for several miles at varying speeds with headlights on. Charge is down to a steady 13.01a at idle.
1996 XJ, is the current regulated from the computer? Could this be my issue?
Drove it for several miles at varying speeds with headlights on. Charge is down to a steady 13.01a at idle.
1996 XJ, is the current regulated from the computer? Could this be my issue?
Last edited by ElMartillo; 11-18-2016 at 08:38 AM.
11-18-2016, 06:37 PM
#10
CF Veteran
Join Date: Feb 2012
Location: central IN
Posts: 2,282
Likes: 0
Received 15 Likes
on
11 Posts
Year: 1997
Engine: 4.0
when did they start putting those battery temp sensors in xjs? i think some 96s had them. i'd doublecheck all of your wiring at every connection before going too much further.
Last edited by s346k; 11-18-2016 at 06:39 PM.
11-19-2016, 06:29 AM
#11
CF Veteran
Join Date: Apr 2016
Location: Pasquotank, NC
Posts: 1,679
Likes: 0
Received 15 Likes
on
13 Posts
Year: 1990
Model: Cherokee
Engine: 4.0
What RPM is your Jeep idling at? My 79 Camaro (apples and oranges, I know) idles around 700 IIRC. The volt meter is down around 12 volts at idle and jumps to 14 once the RPMS get above 1000. The lights noticeably dim at idle. I've replaced the alternator and it still does it. I chock it up to a 37 year old vehicle.
Long story to suggest setting the idle higher during your testing. Shove a dime under the throttle stop to elevate the idle for testing. If it puts out enough voltage at higher RPM I wouldn't chase the issue too much further. You're not at idle long enough to hurt anything typically.
Long story to suggest setting the idle higher during your testing. Shove a dime under the throttle stop to elevate the idle for testing. If it puts out enough voltage at higher RPM I wouldn't chase the issue too much further. You're not at idle long enough to hurt anything typically.