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Discussion Starter · #1 ·
Afternoon guys,

First off, yeah, I searched alrady.  :p

91 RC, 5.9TBI. After the truck sits for more than 2 weeks or so I sometimes get a code 41, and a no charge symptom, always after a battery disconnect as well (truck has a battery switch, flipped off for storage). Usually a key cycle will fix it. A few weeks ago, no luck with the key cycle fixing it though, revving made no difference, tapping on the case made no difference. I was running into a time crunch so I put the truck back in storage, and it started charging as I was doing so. I've noted this behavior off and on for several years, never worried about it since it always went away after a key cycle. It seems to have started after an alternator rebuild.

A couple weeks later I went out since I had some time, started it up, sure enough, code and no charge. B+ at the high current side, 11.8v at both field terminals. Having already looked up the wiring, I bumped the PCM VR wire to ground momentarily, alternator audibly 'spun up' and started charging completely normal, output from the field had dropped to a varying voltage of around 6-9v. A few days went by, went to check on it again, pulled the field wiring off, showed around 3 ohms across the field, same either direction. Connected it all up again, charged fine but it was only a couple days, which usually isn't an issue. No AC on the output side either. Wiring checks out between the PCM and the alternator, around .2-.4 ohms, same for the ASD feed.

Given I'm prepping for a 2500 mile road/wheeling trip in a few months, I gotta make sure it's solid, so now's the time to fix it.

So, my questions are:
1. Does this sound like an alternator issue? Perhaps a solder joint on the rectifier, corrosion on one of the brushes, something along those lines?
2. Does this sound like a symptom of the PCM getting ready to let loose? It's original from '91 (truck has been in the family since 92).
3. If I were to source an internally regulated Denso, is there a way to bypass the PCM regulator AND keep the CEL off? I still have to smog the truck here in Cali. I did grab a replacement reman PCM months back while thinking I had another issue, that PCM was confirmed DOA, so I don't have a ton of faith in those.
4. What logic does the PCM use to set the code? Does it do a voltage check at initial startup, and if no field voltage is detected, it will not provide any ground for the field?

Thanks!
 

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to me, it sounds like you have either a weak connection/near broken wire, or the regulator (which is one of the chips in the computer) is about to die. You can wire in an external regulator as a solution and I do not think you get a check light, but I could be mistaken. The error code works by the computer monitoring system voltage.
 

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Discussion Starter · #3 ·
So I'd need to wire in the external reg and leave the SBEC connected? Interesting.

I do need to pull the alternator apart, check some connections in there, kinda suspicious of it since the issues started not long after a rebuild due to bearing failure.

Thanks for the info.
 

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gsellstr said:
So I'd need to wire in the external reg and leave the SBEC connected? Interesting.

I do need to pull the alternator apart, check some connections in there, kinda suspicious of it since the issues started not long after a rebuild due to bearing failure.

Thanks for the info.
The inspection is free, so definitely check all the internal contacts. I had one once with a defect in a brush spring (warped and too short) leading to poor contact.

Yes, when the computer's regulator fails, the common solution (to avoid paying $300 for a new computer) is to pull the existing field wires and creating a new circuit using the traditional/older external regulator. If you go this route, you *absolutely* want to use a genuine Mopar regulator. The aftermarket is exceptionally poor in quality with these and we frequently see failures right out of the box or extremely premature.
 

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brush contact failure , sitting kin do that , or at least it has done it to me ....  disco both field wires at alt , power 1 field terminal with 12 from bat stud , run a ground to the other field terminal should give ya attempt at 24 volts when started , called full fielding the alt done short time as test only ....
 

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Discussion Starter · #6 ·
I did essentially that without unhooking anything. The momentary hit of ground to the VR side of the field made it sing along like it should.

I'll pull it down and check the brushes. That and solder joints was on my hit list. I may also just ship it to a new old-timey rebuilder a few friends have started using with exceptional luck. The shop that did this one last time started going downhill when mine was done, coulda been cheap parts installed. $100 for a full rebuild sure beats a new one.

The sitting thing really makes me thing connections, corrosion or something along those lines.

Thanks guys!
 

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The 1993 Canyon Sport had an intermittent charging issue and it turned out to be the computer.  I ran wiring and mounted an external oem voltage regulator and it works perfect.  It was very easy to do and it’s nice knowing it will be easy to fix if it ever quits charging again.  I didn’t do a thing to the alternator.
 

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gsellstr said:
I did essentially that without unhooking anything. The momentary hit of ground to the VR side of the field made it sing along like it should.

I'll pull it down and check the brushes. That and solder joints was on my hit list. I may also just ship it to a new old-timey rebuilder a few friends have started using with exceptional luck. The shop that did this one last time started going downhill when mine was done, coulda been cheap parts installed. $100 for a full rebuild sure beats a new one.

The sitting thing really makes me thing connections, corrosion or something along those lines.

Thanks guys!
The only issue with that thought is that *if* it isn't the alternator, you'll have spent $100 and still have to put the external regulator on... And since full-fielding the alternator works, it makes me think the alternator is okay.
 

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Discussion Starter · #9 ·
I do get that as well. Here's my thought process...

PCM does a voltage check at startup, to see if ASD voltage is present at the VR side of the coil. If so, no DTC, VR circuit goes live and sends the variable ground for the field. If NO voltage is present (such as a brush that's hung, bad connection, etc), then the PCM sees no voltage at the VR side, determines it's open, shuts off the VR control, so no charging.

Supporting this theory, is the fact it usually is fine after a key cycle, only one instance it hasn't cleared itself until about 10 minutes in. It is also fine after the initial occurrence, following sitting long term (enough for corrosion to begin). Lastly, this issue started not long after the last rebuild. The shop that did the rebuild didn't even swap the rectifier pack, which failed approx. 3 months later, and was replaced with an aftermarket one I grabbed from the local chain store.

I will probably look into getting an external regulator kit just to have in the toolbox before the trip this fall though, just for my own peace of mind.
 

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I had an alt recently , older spade connector field style , she go to work (dark) everything fine , JUST make it home battery down .... I wiggled field wire and holder in process , bingo , charge , snug screw to holder ok fixed ....
( newer rebuilt alt ) 2 days later SSDD .... wiggle charge screw tight still ..... r/r alt with used off shelf .... fixed .... so it has a double grove pulley and only needs 1 ....... still lined up ......  ;D 
 

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Discussion Starter · #11 ·
I'm kinda hoping it's something stupid like that. lol

Asked another Mopar nut at work, got a regulator and pigtail headed in tomorrow, since he can't use em anymore on his Cuda. That'll cover the backup for the Moab trek, then teardown/rebuild/whatever on the alternator to see what's what.
 

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Discussion Starter · #12 ·
Parts cannon fired. I was thinking of just having the alternator rebuilt locally, then I checked Summit. Reman'd BY Denso, 120A for $86 plus a core, throw in some brake pads I need anyway and free shipping, keep the old one for diagnosis on the bench, refurb, stockpile, kinda hard to say no. It was gonna be $100 just to rebuild this one locally. Worst case it makes no difference and I put on the external reg for the trip, best case I never have another issue with it again.

Then Prime day happened. 100' of 7/16 ARE winch rope, a Warn fairlead and winch cover. My credit card hates me right now. lol
 

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snatch blocks are handy while yer at it .......... lol  oh hey did ya know the fsm's show a fuseable link in the HOT wire to the alt ? looks to be somewhere ON the engine , a part OF the main alt lead ... I say that cause of yer winch , and its draw.....
 

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Discussion Starter · #14 ·
Already got a snatch block in the truck, been there since the winch was installed, so that's handled. Also bumped the alternator high current side up from factory wiring to some #4 I had laying around, back when I installed the winch, made a rather significant improvement in charging voltage, go figure. lol
 

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yes , my plow truck , a '91 still has the oem wire there , with a OLD lift only myers pump , been meaning to change that wire , volts gauge drops to 8 or less on a lift of ? 9 foot homemade steel plow .... easy to drain battery plowing, never seems to bother in good weather so ..... it remains ... that wire is 1 thing a carbon pile load tester is good for ... 
 

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dodge82273 said:
yes , my plow truck , a '91 still has the oem wire there , with a OLD lift only myers pump , been meaning to change that wire , volts gauge drops to 8 or less on a lift of ? 9 foot homemade steel plow .... easy to drain battery plowing, never seems to bother in good weather so ..... it remains ... that wire is 1 thing a carbon pile load tester is good for ...
I've got 2 gauge wire and a 200 amp alternator. Got tired of everything dimming and almost dying when working my plow lol.
 

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Discussion Starter · #17 ·
That's one thing I won't dick around with...factory high current wiring. It's junk in so many cases, and so easy to upgrade to legit wiring that makes a big difference in so many areas. With the exception of the wife's bone stock car, the rest of the fleet is all upgraded to #4 at least. Thinking back the Dodge may be #2 as well, forget where I used that run. Hard not to as well, when you can find so many cars at the yards, previously equipped with big stereo systems, that they left the #2 or #4 wiring in the car. Takes just a couple minutes to have 15' of beefy wire that costs a couple bucks at the most. lol
 

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alllll right guys , ya made me feel bad enough,  I'll do it this summer before we're hauling firewood up to the house
( its the next time that truck will get used , plateless...) 
 

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Discussion Starter · #19 ·
Guilt trip completed! lol

Anxiously waiting on shipping companies today and the rest of the week. Brake pads, winch cover and hawse today, ARE rope on friday, no idea on alternator since it drop shipped from Denso's warehouse somewhere, Summit has no info.
 

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Discussion Starter · #20 ·
Ok, new denso reman alternator in, no change in the DTC. Definitely handles the winch a lot better than the old one though. Spooled up 100' of synthetic rope tonight, 30 second pulls, 3-4 minutes cooldown in between, voltage during a pull dropped about a volt, would have been 1.5-1.8 on the old one.

So, did some testing. Checking on the VR signal line to the PCM to battery ground, I was showing 12v with the key off. That makes me curious, since there shouldn't be any voltage either coming from the SBEC or from the ignition switch so I'm not sure what's going on. I didn't think about it until later, but I need to pull the wires off the alternator, see which leg has 12v on it with the key off.

The other thing I'm wondering about is if there's a cap that's getting charged up on the SBEC when it sits, then when I give a momentary short to ground on the VR line, it drains the cap and the system starts working again.

Anybody know much about the logic side in these old SBEC's?
 
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