Charging issues

Timberbeast · Oct 2, 2019

I have a 93 Wrangler with 4.0
It started having issues charging (which often went undetected thanks to a deep cycle battery) if it sat for a day or two the battery would be flat.
Last time it went out it was charging at 14 volts and than most of the gauges including the tach and speedo quit working and eventually had to be trailed home.
I'm not having much luck finding any info on diagnostics for this year, even which terminal is which on the alternator.

It has the Denso alternator controlled via the PCM, can't find a new PCM and don't want to throw 250$ parts at it hoping to fix the problem and I don't want the bypass kit.
The alternator and battery test out fine.

Anybody manage to cure this ailment?.

Scouter · Oct 27, 2019

With the bypass kit you don’t want.

12b · Oct 29, 2019

Why may I ask do you not want an external voltage regulator?
Have you physically cleaned all the grounds, battery connections, alt connections?
Where did you get the battery checked out?
It could very well be a bad battery even though you think it's good

Here's a link to FSMs plenty of diagnostic info in these

https://www.dropbox.com/sh/0vfmk6jc5...v7lceZk7a?dl=0

aldo90731 · Nov 30, 2019

Moved this thread from the How to Videos to the Tech section, since it does not have a video.

8thtimer · Dec 1, 2019

Can a deep cycle battery supply enough amperage to crank up a engine? I was under the impression that's a no go as there made for long duration at lower amp output. 14.3 is right on for a good working alternator also.

Luckymac · Dec 1, 2019

Timberbeast, Find a post by Got it at last. In his signature there's a free link to several Factory Service manuals and a couple Factory Parts Manuals.
Open that link and click on the manual that you need.

You state that the last time it went out it was charging at 14V. Where did you take this measurement, at the alternator or the battery?
Then after you took that measurement the gauges quit working and the Jeep had to be towed. The Jeep will drive with non-working gauges, so something else occurred that required the vehicle to be trailered. You haven't told us what that was.

I would take the battery to a battery store to be load tested.
Some parts store counterfolks might know how to load test a battery. I bet many of them don't know how to do it properly.
Even an employee at a battery store (Batteries Plus for example) isn't a guarantee that they know how to do a load test properly. If you have access to a known to be good battery, you could install it to see if the condition continues with another battery.

I suggest you clean your battery terminals and posts (+ & -) to clean shiny metal and put them back with a dab of dielectric grease. Then, do the same thing to the grounds. The (-) cable to the block, the strap from the back of the head to the firewall and a block and/or tub cable/strap to the frame if your '93 has such a ground.
Then remove, clean the (+) cable at the starter and the other connections there too.
Put everything back with dielectric grease.

If you took the 14V measurement at the battery with the engine running and the cables attached, your alternator, regulator and battery seem to be working. Operative word is "seem". One of them is bad.
Your alternator may be failing and only working part of the time, thus the Jeep quits while running. The fact that the battery goes flat if the Jeep sits for a few days indicates a bad diode in the alternator.

A used alternator from a Grand Cherokee is supposed to have a higher output than the stock YJ alternator. There might be some slight mods necessary to fit a GC alternator to a YJ, but I seem to remember that it's a simple and easy swap. Other posters that have done it might chime in to give more details.

If you conclude that your PCM isn't properly regulating the charge current, check out WranglerFix. The TJ guys seem to have a great regard for him. He appears to have found a cure for the common failed PCM issue on 6cyl automatic '05-'06 TJs. His website states he works on YJ PCMs also.

Keep us posted on what you find and how it goes. Don't disconnect the battery while the Jeep is running to see if the alternator is working. Other posters can tell you what'll get fried.

Good Luck, L.M.

wcjeep · Dec 1, 2019

It's not a good idea to use the factory alternator to charge a near dead battery. The factory alternator duty cycle is low. Use a battery charger to slowly bring the battery to full charge.

Have you looked for offline amperage draw? Something could be on in error. Short to ground? Pull the negative battery cable. Place a multimeter in Amp mode between the cable and battery. Be sure the vehicle doors are closed. All lighting is off. What is your amperage draw? It should be .1amp or lower. Much more than .1amp means vampire draw.

Battery cables can go bad below the insulation.

agalloch07 · Dec 2, 2019

The factory + cable from alternator to battery is poorly constructed. It comes off the + lug on the alternator then runs up to the PDC box where it is connected to 2 much smaller wires that run into the PDC then though 2 fuses and then to the battery. They didn't solder or crimp the 3 way connection they just stripped about an inch of insulation off each of the 3 wires and shrink wrapped them together. You can upgrade the cables and bypass the PDC box and run a fused cable straight to the battery.

steves92 · Dec 2, 2019

agalloch07 said:
The factory + cable from alternator to battery is poorly constructed. It comes off the + lug on the alternator then runs up to the PDC box where it is connected to 2 much smaller wires that run into the PDC then though 2 fuses and then to the battery. They didn't solder or crimp the 3 way connection they just stripped about an inch of insulation off each of the 3 wires and shrink wrapped them together. You can upgrade the cables and bypass the PDC box and run a fused cable straight to the battery.

I’d be interested in this! Do you have a link or source? So that fuse in box can become another option for something else?

Sent from my iPhone using Tapatalk

12b · Dec 2, 2019

As far as I know the PDC can not be bypassed there needs to be high amp and 12V running through the PDC or your Jeep won't run. Why half A$$ something when it's easy enough to replace the cables in the stock configuration.

Luckymac · Dec 2, 2019

Original post by @Timberbeast was 10-02-19 (two months ago). I wonder if he ever resolved his issue?

Good Luck, L.M.

Timberbeast · Dec 3, 2019

Nope I haven't fixed it yet. I thought I had finally forced it to burn up the defective component so I could locate it but no such luck.
I replaced the PCM with one off Ebay (Note: these are getting hard to find and EXPENSIEVE so don't pass up on a spare!, makes a guy wonder what I am going to do when the last one burns up and I can't replace it)

My alternator has been tested twice.

All four circuits from the alt to the PCM, ign, batt, ground test out excellent, not with a large load but that should burn out any serious resistance.

Battery tests out fine.

It still randomly doesn't charge.

I plan to install an ammeter and would like to find a way to monitor the field/sense circuit to see what is actually going on when it quits charging.

The part about the low duty on the stock alt would explain why it seems to behave for a while when I charge the battery.

I also had my USB charger unhooked, it was drawing a lot. not the root cause but it didn't help.

You have to run the battery cable to the PDC.

I have done all the basic stuff long ago. I have spent a lot of time as a professional mechanic, I had 13 forklifts to maintain when I worked for the sawmill.

On a sad note I had to have my my jeeping buddy of almost 13 years put down wed because of cancer. :rip: Smitty

Thanks for the help thus far.

Luckymac · Dec 3, 2019

Luckymac said:
If you have access to a known to be good battery, you could install it to see if the condition continues with another battery.

If you took the 14V measurement at the battery with the engine running and the cables attached, your alternator, regulator and battery seem to be working. Operative word is "seem". One of them is bad.
Your alternator may be failing and only working part of the time, thus the Jeep quits while running. The fact that the battery goes flat if the Jeep sits for a few days indicates a bad diode in the alternator.

Good Luck, L.M.

Have you tried a known to be good battery?

Did you get 14V at the battery with your engine running?

Let us know.

Good Luck, L.M.

Timberbeast · Dec 3, 2019

I still suspect the alternator, the charging rate will go from 15-9 volts (mind you the voltmeter comes thru the PCM as well so it doesn't show what the actual alt output is, only the system voltage.

Most of the time when it starts it will jump right up and maintain around 14 but others it stays down around 9, any less and I loose everything on the dash and have 20-30 miles before the battery gets too lower to run the fuel pump.
I have had the battery tested and have a load tester myself. Heavy use like winching doesn't affect the performance.

Krangler87 · Dec 3, 2019

Maybe a intermittent loss of signal to the alternator due to a intermittently poor/loose connection to the alternator, or a defective alternator...........

Luckymac · Dec 3, 2019

Krangler87 said:
Maybe a intermittent loss of signal to the alternator due to a intermittently poor/loose connection to the alternator, or a defective alternator...........

Electrical problems are easy to cure. The problem with electrical problems is that it's difficult to find the cause.

Krangler87 may be on to something.
Starting with the alternator and using a strong light, I suggest disconnecting the alternator contacts and examining the plug and the ring terminal. Pull and twist each wire while holding the plug and the single wire while holding the ring terminal. Look for any corrosion or fraying. Put it back with dielectric grease.

Then, follow the red wire to the PDC and do the same thing there. Then after checking out the schematic, continue on to all the other connections in the charging circuit.

My '87 is somewhat different than your '93 so my suggestion may not be exact, but you get the idea. Check all the connections in the entire charging circuit. Pull and wiggle each wire in each plug while looking foe any corrosion or questionable condition.

Good Luck, L.M.

Timberbeast · Dec 3, 2019

Been there, done that and all the connections ring out fine.

The Denso has the field, ground and sense wires all moulded into a plastic block with 4 ring lugs sticking out of it, different than your standard 3 wire GM alternator. If it was that style it wouldn't be an issue getting it to charge.

At some point I will have to probably rewire the whole machine but it will be a couple years and building a shop before that happens.

12b · Dec 3, 2019

I know you stated that you did not want to use the external voltage regulator. Plain and simple, it will cure your problem once and for all.

How many man hours and how much money do you want to invest in making the stock system work? You've already bought a PCM that you didn't need.

https://alternatorparts.com/external-voltage-regulator-high-output-alternator-kit.html

My suggestion (from experience) is to power the external VR through a relay

agalloch07 · Dec 4, 2019

steves92 said:
I’d be interested in this! Do you have a link or source? So that fuse in box can become another option for something else?

Sent from my iPhone using Tapatalk

You cant get rid of the box it controls other things. If you upgrade the charging system with a bigger alternator the factory wiring is not built to handle it. You re-rout the factory + off the alternator (fused) directly to the + battery post.

You still need a cable running from the + battery post the the PDC but it still powers the old cable that used to go to the + alternator post. So you either need to pull the 2 50 amp maxi fuses to kill it so it wont arc. I kept the old cable live and attached it to a power post on my fender so i can hook up stuff like my air compressor, Headlight relay conversion and whatever else i add to it. When we did the big wire upgrade on my friends YJ he removed the old wiring all the way back to the PDC and just got rid of it.

I had better pictures of it but i cant find them all of my new battery cables are 2 AWG. And instead of the PDC acting as the fusible link for the alternator i put in a Blue Sea Systems fuse block in and a larger fuse that can handle the amperage of the 120 amp alternator.

Charging issues

Timberbeast

Scouter

12b

aldo90731

8thtimer

Luckymac

wcjeep

agalloch07

steves92

12b

Luckymac

Timberbeast

Luckymac

Timberbeast

Krangler87

Luckymac

Timberbeast

12b

agalloch07

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