dan10101

My charging system is doing weird things.
1998 XJ 4.0l

After charging the battery.... 12.4v at the batt
It starts right up and runs fine. But the volts on the dash show 11v or less.
Then after it runs for a while 5m-10m, the battery voltage starts dropping, then finally it starts running really bad and dies. won't start.
I can read the voltage at the battery and it shows 7v and climbing all the way back up to about 12.4 v.
But it still won't start without charging.

What I've done...
Changed the brand new Battery to a another known good batt. Both test good.
Changed the alternator.
Checked, removed and cleaned all the grounds in the engine bay. (any others to check?) (they were fine looking btw.)
Still the same problem.
Changed the PCM. Still the same.

Still the voltage on the dash shows 9-11v. Sometimes drops to 9v instantly.
Did the dash check, checks fine.

Has anyone done the external regulator mod?
My next steps:
Another alternator
Then the external reg mod.

Tbone289

Have you tested the battery temp sensor? It's the spring-loaded sensor in the battery tray. Disconnect it and test resistance at room temperature (70-80 degrees F). It should be in the 9K-11K ohms range. I doubt this is the problem, but I don't have any other bright ideas at the moment.

Was there any change at all when you replaced the alternator?

dan10101

I'll check that. It was on my list and I forgot it. It wasn't there when I got it. (no battery box) and the replacement box didn't have it. I just picked up another box with the sensor, now I just need to find it in the harness. I'm with you that it shouldn't make much difference, but maybe not being plugged in could be a problem.

No change with the alternator, but it was an almost new, used one. I'm putting on another new one today just to make sure.

thanks

dan10101

I found the plug for the temp sensor and tested the ohms. it was about 16k but it's colder here. So I plugged it in and no change. Then I changed out the alternator that was sitting on the bench dying to get into the game. Again, no change. It's just really strange with a charged battery, it starts right up, then slowly the voltage at the battery starts dropping down to about 7 volts, then the engine dies and won't start.

dan10101

The PO was going to use it as a Jeepspeed racer. So a lot of electrical connections aren't connected. Some of these are for the electric fan, and maybe controllers, but I don't know what the rest are for. Just trying everything at this point.

https://www.cherokeeforum.com/attach...1&d=1507582566

https://www.cherokeeforum.com/attach...1&d=1507582566

dan10101

The bottom one in those pictures is for the batt temp sensor. So, one down...

tech

Did you test the wiring to the alternator the pos wire and the wiring that goes to the computer ?

freegdr

You just buy this ?

Tbone289

Wow. Well, they all look pretty clean at least!

freegdr

Thats alot of unused plugs there only gonna reach so far gotta plug in somewhere..

dan10101

I think that's where I'm going next. wiring, ugg


Yes, non running


the whole jeep is very clean, no rust, but I pulled the grounds off anyway and cleaned them to make sure. Maybe I need to unplug and replug connectors...

Well, now that I know where one of them goes, I have a lead... I'm sure some went to the factory fan setup, but it was already replaced with a 3 fan setup. I'll see what makes sense. the problem is there isn't anything that needs a plug in that area.

dan10101

Wahoo! It's working! One connector not connected fixed 2 problems. Now it starts without bypassing the NSS and it's charging. I have some wiring cleanup to do with a crimp connection gone bad but it's working. The good news in all this is there probably isn't any bad parts so I have spares.

When the PO (previous owner) started dismantling this for a racing setup, he disconnected a bunch of wiring. I was looking for something to plug it into, but it was in fact another wiring harness and apparently a very important one.

A nice 10 min test drive confirms it's working. Charging just under 14v by the dash gauge.

Thanks everyone for your help!

Tbone289

Jeep pics!

dan10101

I'll try to get some action shots before it breaks again!


https://www.cherokeeforum.com/attach...1&d=1507606669

tech

That's a good looking cherokee , what hood is that ? and is that a 4x4 ?