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-   -   battery charging issues & 50A MUX/T Tow Circuit (https://www.jeepforum.com/forum/f13/battery-charging-issues-50a-mux-t-tow-circuit-4391179/)

Rick1955 03-15-2020 03:46 PM

battery charging issues & 50A MUX/T Tow Circuit
 
1997 jeep Grand Cherokee.
Symptoms: 1) Battery not at a full charge rate. 2) Current drop of 3.5A on 50A MUX/T Tow fuse circuit. Are these two related?

Here is what happens: Starts fine. Voltage indicator on dash shows 14V, immediately drops to 11.5V, then after a couple of minutes it flat lines to zero volts, then eventually pops back to 11.5V & repeats this cycle from 0 to 11.5V.

Battery: Fairly new, new post clamps. Multimeter shows 12.3V when battery is disconnected. 11.8V when cables are connected. 11.75V when engine is running.

Alternator: New. Then re-tested at Schucks & Autozone...they said it is good. Schucks said they will not replace if they test it good. Voltage drop on neg side is zero volts. Voltage drop on pos side to B+ is 1.5V

Replaced my PCM also. ouch$$$

Is my new alternator really bad or could my 50A MUX/T Tow circuit be affecting the charge? I like to figure things out myself before taking to an expert mechanic, but, perhaps it is time to take it in. Any suggestions? p.s. thank you in advance! You guys have already been a lot of help!

GOLDWING 03-15-2020 03:58 PM

Quote:

Originally Posted by Rick1955 (Post 40904051)
1997 jeep Grand Cherokee.
Symptoms: 1) Battery not at a full charge rate. 2) Current drop of 3.5A on 50A MUX/T Tow fuse circuit. Are these two related?

Here is what happens: Starts fine. Voltage indicator on dash shows 14V, immediately drops to 11.5V, then after a couple of minutes it flat lines to zero volts, then eventually pops back to 11.5V & repeats this cycle from 0 to 11.5V.

Battery: Fairly new, new post clamps. Multimeter shows 12.3V when battery is disconnected. 11.8V when cables are connected. 11.75V when engine is running.

Alternator: New. Then re-tested at Schucks & Autozone...they said it is good. Schucks said they will not replace if they test it good. Voltage drop on neg side is zero volts. Voltage drop on pos side to B+ is 1.5V

Replaced my PCM also. ouch$$$

Is my new alternator really bad or could my 50A MUX/T Tow circuit be affecting the charge? I like to figure things out myself before taking to an expert mechanic, but, perhaps it is time to take it in. Any suggestions? p.s. thank you in advance! You guys have already been a lot of help!

If your "new post clamps" have the cable pinched between a piece of tin and the actual clamp, get rid of them. If you have crappy cables and dirty corroded ground points on the engine and body/chassis then take care of them. After that you may find that the new PCM was not needed.

GW

Rick1955 03-15-2020 04:21 PM

Thank you GW. I do have the tin clamps, will fix this. Cables & grounds are ok.

StPaul59 03-15-2020 07:21 PM

Quote:

Originally Posted by GOLDWING (Post 40904063)
If your "new post clamps" have the cable pinched between a piece of tin and the actual clamp, get rid of them. If you have crappy cables and dirty corroded ground points on the engine and body/chassis then take care of them. After that you may find that the new PCM was not needed.

GW


Good God I hate those clamps with a burning passion!

GOLDWING 03-15-2020 07:47 PM

Quote:

Originally Posted by StPaul59 (Post 40904235)
Good God I hate those clamps with a burning passion!

I think that they are maybe good enough to get you home if you somehow have a problem on the trail. Beyond that, they allow lots of mechanics to earn easy money since they can cause symptoms that mimic all manner of expensive issues.

GW

ZblackliZard 03-17-2020 06:37 PM

1 Attachment(s)
Quote:

Originally Posted by GOLDWING (Post 40904063)
If your "new post clamps" have the cable pinched between a piece of tin and the actual clamp, get rid of them. If you have crappy cables and dirty corroded ground points on the engine and body/chassis then take care of them. After that you may find that the new PCM was not needed.

GW

Could you clarify this clamps story? I have some issues with my battery charging and I use clamps like this: could they be the problem?

StPaul59 03-17-2020 06:43 PM

Quote:

Originally Posted by ZblackliZard (Post 40905851)
Could you clarify this clamps story? I have some issues with my battery charging and I use clamps like this: could they be the problem?



These absolutely suck. You can't ever get them to stay tight..

ZblackliZard 03-17-2020 06:46 PM

Quote:

Originally Posted by StPaul59 (Post 40905857)
These absolutely suck. You can't ever get them to stay tight..

What should i get then?

GOLDWING 03-17-2020 06:52 PM

Quote:

Originally Posted by ZblackliZard (Post 40905851)
Could you clarify this clamps story? I have some issues with my battery charging and I use clamps like this: could they be the problem?

The ones in your pic are just a nicer version of a poor design. Crushing a stranded wire cable would not be so bad if oxygen couldn't get into the connection and cause corrosion. The cable works best with a soldered connection to a terminal lug which is bolted to a marine or military style battery terminal.

GW

ZblackliZard 03-17-2020 06:58 PM

Quote:

Originally Posted by GOLDWING (Post 40905869)
The ones in your pic are just a nicer version of a poor design. Crushing a stranded wire cable would not be so bad if oxygen couldn't get into the connection and cause corrosion. The cable works best with a soldered connection to a terminal lug which is bolted to a marine or military style battery terminal.

GW

Get it now Thanks for the clarification!

StPaul59 03-17-2020 10:20 PM

I just bought new 4ga precut wires of appropriate length from the battery section (any auto store) and cut the silver lugs off and replaced them with copper lugs. You could keep what's on there but the copper is flatter and easier to work with. The lug going to the alt will most likely have to be trimmed with a dremel to fit. I just reused the starter wire and put a lug on It, it still starts fine.

Rick1955 05-13-2020 01:27 PM

1997 Jeep Grand Cherokee UPDATE: Don't Always Trust Alternator Bench Tests
 
1997 Jeep Grand Cherokee UPDATE: Don't Always Trust Alternator Bench Tests!

Just wanted to provide an update regarding two issues with my jeep:
1) 50A Mux/T Tow circuit
2)Alternator not charging battery

These two symptoms were unrelated. Performed voltage drop test to determine why my battery was draining overnight.The 50A fuse under the hood lead me to the F7 fuse in the cab. Finally figured my dimmer switch was the problem & replaced it........now, no battery drain!

Finally just went ahead & replaced my alternator, now the electrical system is working fine. I did take my one-yr old alternator to several shops for bench testing...they all said it was OK. I purchased it at Oreillys, but they would not exchange it based on their "good" bench test. Turns out this was a bunch of BS! In the meantime, I replaced my cables, connections, checked all grounds, fuseable links, even my PCM, just could not figure it out. Yep, it really was the alternator.

I appreciate the advice & suggestions you all have provided on the Jeep Forum. Thanks. Rick.


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