ElMartillo

91 4.0 4x4 Sport

Charging at 14.5 or so while running.
Drops to low 13’s at shutoff, I can watch it drop a tenth of a volt every 15 seconds or so.
After sitting overnight it showed 12.3 volts before any crank attempts.
Cranking voltage is around 11.5 or so.
starts noticeably slow, esp while hot.

Bad battery or bad starter?

Cheers!

4.3L XJ

It is fine. Normal

ElMartillo

So the starter/connections would be suspect?

agreen

If you have cranking issues, start with cleaning your connections, especially the grounds.

4.3L XJ

You didn't say you had starting issues, just wondering about voltage. So what is happening?

lawsoncl

Clean connections and possibly replace the battery cables. 20-year old battery cables can be rotten inside.

cruiser54

I'd get the battery checked also. How old is it?
Is your starter covered in oil?

ElMartillo

Starter turns noticeably slow. Worse when hot.

New cables and milspec lugs this year.

Battery was new in 02/20.
No oil on starter, though the starter came with the vehicle. Do my voltage readings suggest bad batt?

cruiser54

I don't see why the voltage would continue to drop like it does with everything off.

ElMartillo

I’ll check voltages again today. See how it behaves.

Lzysmrf

Your battery voltage is fine. I would suggest cleaning first. Both positive and negative terminals on battery and starter. then you can pull both the starter and the battery to have them tested. Sounds like a starter problem

BlueRidgeMark

Voltage dropping when turned off has absolutely nothing to do with your starter.

Low voltage will cause the starter to turn slowly, but a bad starter is not causing your voltage to drop.

You have a parasitic drain somewhere, or a bad battery.

You MAY also have a starter problem, but fix the drain problem first. Only then can you judge whether or not you have a starter problem.

Lzysmrf

A battery at rest with no charging on it will read about 12.2v
A battery with vehicle running will read 14.4v
after shutting of the vehicle, the battery will automatically drain down to about 12.2v
if it is still draining any lower you have a parasitic drain.
a slow turnover could be a bad connection, bad starter, or a bad cell in your battery
if you're reading about 9v or more during cranking the your battery should still be good. TEST TO CONFIRM
my opinion is a starter problem

ElMartillo

After not starting it at all yesterday, battery shows 12.54 volts. Looks like the battery is fine, I’ll check connections to starter, though I may just order a replacement. I have three XJs and it couldn’t hurt to have one on hand.

Thanks for the info, folks!

robsjeep

A failing solenoid can also cause these symptoms you have. If you measure the voltage drop across the solenoid, i.e. the voltage that the starter is getting during cranking, you thenhave tested the solenoid. You got nine volts at battery while cranking, but the next question is, did you get nine volts at the starter motor or not?
It used to be common to replace only one or the other , starter or solenoid after testing to see which one was bad, as often one was still good. This is how the solenoid was tested, read the drop across it or calculate that drop by subtracting the starter motor input voltage from that of solenoid input voltage while cranking. the drop across the cables and its connects can also be evaluated this way, to test cables, read the voltage between positive battery terminal and the positive input on the solenoid while cranking, you want a very low drop, if high drop voltage is found, the cables and connectors are suspect.
You test the negative side by measuring the drop from the negative battery post and the grounded case of the starter motor during cranking. if that is a bad high value, then look into the ground connections from battery to starter for the problem.

Only after you read directly or calculate from indirect measure the actual voltage delievered ACROSS the starter during cranking should you determined if starter is bad or not given the symptoms you are experiencing.

So first step is read the voltage while cranking of starter motor positive terminal ( the fat wire, not the skinny solenoid switch wire) across to the fat ground wire at starter. Reading this voltage at the battery is no substitute as bad cables or connections can give a false reading that the starter is bad.

If the voltage at the starter is good, then that means battery, the power connections, and cables are excellent.

Also, a weak key switch voltage, the skinny wire at solenoid that triggers the solenoid, can cause the solenoid to not slam closed with the required force to make a good electric contact to supply the starter motor with power. so if you find poor voltage across the starter, make sure your solenoid trigger i.e. key switch voltage is up to the stuff.