1996 Charging Issues

[J-Roc]

I have been searching and still am but I haven't found many people sharing the same symptoms...

Specs
4.0, auto, 1996

What I have done, warrantied battery (new within the last month). I just replaced the alternator tonight (ZJ "136 amp" unit) since I was sure this was the problem.

Turns out my alternators output is not increasing when loads are put on the system... I cannot for the life of me figure out why... tested with a volt meter, printed out diagnostics off of Mitchell on Demand (garbage program FYI)

With the engine idling the alternator charges are 13.8v, when I rev it up to 2500rpm it continues to charge at 13.8v so it's like it's in some sort of limp mode... as if it isn't receiving a single from the pcm to increase the voltage.

The Jeep hasn't left me stranded yet but when I have my headlights on you can see it's hovering around 13v, if I put the blower/rear defrost/stereo on the voltage will drop down to 12.3v

It had these same symptoms with the OEM 117 amp unit I just yanked out and now it's doing the same with the new ZJ alternator.

I have not upgraded the wiring but I did a Go-Jeep headlight upgrade after my harness melted last year so I made some new grounds. However this problem has been happening since before then...

I'm at a loss and I've dropped a lot of money already :twak: and I still can't figure this out. If I drive during the day it's fine because it'll just barely charge the batt since I won't be running any load on it minus a piss poor excuse of a stereo...

 

[joe_peters]

Well, 91+ XJ have the Nippon Denso alternators, and they are regulated by the PCM--I would dig out the FSM and a multimeter and start testing the harness between them.

 

[J-Roc]

Unfortunately I do not have access to a FSM... as I am not the original owner of the vehicle and it is long gone. That is why I resorted to Mitchell but it is so vague... it says test the black/grey/white connectors at the PCM yet it does not explain which wires control what...

 

[Wayne Sihler]

You could also check the battery tray for the battery temp sensor. It too controls(has input) on how much the PCM will allow the battery to be charged,by the temp of the battery.

Wayne

 

[J-Roc]

You could also check the battery tray for the battery temp sensor. It too controls(has input) on how much the PCM will allow the battery to be charged,by the temp of the battery.

Wayne

There was nothing referenced in Mitchell for testing that sensor in the tray... How would I go about testing it? I have seen it but not sure of it's purpose (besides what you have told me)

What would happen if I were to disconnect it?

I should also mention that I am running a Purple Haze Orbital Battery (AGM)

 

[Wayne Sihler]

I think it would throw a code,or not let the battery charge--. Also check the ASD relay,My 96 FSM shows that in the charging circut also.
To check battery temp sensor---attach ohmmeter to leads of sensor >at room temp 25*C (75-80*F). Ohmmeter reading of 9 to 11K ohms should be observed.
If readings above or below spec > replace sensor

Are you getting any codes in the DTC ?

Wayne

 

[J-Roc]

Nope... and that's what is boggling my mind LOL! I'll try that test today... I honestly hope it's just crappy wiring so I can upgrade all of it... It doesn't seem that PCM Modules fail all too often so I want to try and rule that out for now... :doh:

 

[Wayne Sihler]

All of the other tests involved hooking the Alt up to a machine to test the output and diodes & stuff..more equipment than the average person would have.
Hope you get it solved

Wayne

 

[J-Roc]

All of the other tests involved hooking the Alt up to a machine to test the output and diodes & stuff..more equipment than the average person would have.
Hope you get it solved

Wayne

Yea... I realize that but since the alternator is brand new as of yesterday I believe the alternator is fine... I bet the old one is fine too (minus the bearing starting to go). I'll keep you guys posted.

 

[joe_peters]

1. Owner's manual comes with the vehicle--if you want one hit the salvage yards and check the glove boxes. The FSM--Factory Service Manual--is something you are going to have to buy. Haynes/Chilton/Mitchell manuals should be hung in the outhouse now that Sears no longer sends out catalogs. Bishko has LICENSED factory service manuals on CD and reprints. The CDs are PDF format, can be copied to your harddrive, are searchable, and you can print them out. Bishko: http://www.autobooksbishko.com/index.html You can find the Bishko manuals on eBay, new, cheaper than from their website.

2. Most chain parts stores will test your alternator for free. HOWEVER, their equipment seems to have frequent FAILURES to correctly test the Nippon Denso externally regulated alternators.

3. Reman stuff has become notorious lately for poor quality. Getting a new off the shelf alternator/starter/what ever is not unheard of.

You really are going to need the FSM driving an old Jeep, or you can make the dealer's day by funding his kids through Harvard.

 

[J-Roc]

I work at a Autoparts Chain store lol so I am aware of the junk quality and alternator testing machines which are crap (along with midtronics)

I'll keep ya posted tonight on the results of the diag I'll be having done... :doh:

 

[joe_peters]

Ok, good luck!

 

[J-Roc]

Updates but NO good news...

-Fusable link wire sheath was cracked so we cut/soldered/shrink tubed the wire to prevent further corrosion... I want to replace this

-Back probed the green wire going into the PCM and only managed to detect 10v going to the computer so we cut the wire and ran a jumper wire from the back of the field terminal to the computer... same results with voltage even with the jumper so we re-soldered that connection as we determined that there was no resistance from that signal wire

-Tested Battery temp Sensor... found out that it was only reading at 5k ohms

According to Wayne Sihler above, the resistance reading for that sensor is spec'd at 9-11k ohms so I will be investigating this further...

Disconnected Battery Temp Sensor and Observed NO CHANGE

Battery is charging at 13.8v unloaded and around 13.4v with full loads at idle, revving engine to 2000rpm does not increase charging voltage or output... idling produces the same results

Back to the drawing board :compwork:

 

[Shorty]

I'm not sure where the "problem" is. What are you expecting to see at the battery with full load at 2000 rpm? I would think that 13.4V would be more than adequate to keep up with accessory demand and maintain a fully charged (12.65V) battery.

The PCM is going to regulate output to match demand, so it appears that it's functioning correctly. You will need to increase demand via greater external load to witness higher amperage output.

edit- in re-reading the first post, I see a drop to 12.3V under full load at that time. If it's still doing this, I'd look into upgrading the wire returning power to the battery. It was never designed to carry the
136amp output and may be the turd in the pool.

 

[joe_peters]

edit- in re-reading the first post, I see a drop to 12.3V under full load at that time. If it's still doing this, I'd look into upgrading the wire returning power to the battery. It was never designed to carry the
136amp output and may be the turd in the pool.

This should help: http://www.olypen.com/craigh/charge.htm

 

[J-Roc]

Thanks for the link... I have read it before and re-read it last week... I have already been in touch with 5-90 to eliminate some of the "problem areas" :yelclap:

 

[J-Roc]

Couldn't edit last post...

Replaced Battery Temp Sensor since the Ohm reading was not within spec (reading @ 5k) no change...

Now I'm just throwing parts at it since I don't know wtf is wrong with it... I will be doing 5-90's battery cable upgrade and that is my last saving grace... after that I will have replaced everything excluding the PCM. I do have access to a free spare so it may be a window of opportunity worth exploring.

I am completely clueless at this point... and I cannot believe someone hasn't had a similar issue :wow:

 

[joe_peters]

Before you throw in the towel, read this article: http://www.motor.com/article.asp?article_ID=1203

Check the section on Chrysler charging and building your own test harness.