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6.5 to 5.9 Cummins Alternator Help

FellowTraveler

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Are these problems only related to the denso alternator?
We are talking Denso here and rotor draw dictates what regulator to use.
"Regulator ground is a toss of the coin" however; a clean ground from it to the Denso case is suggested.
I sandpaper or wire brush all alt brackets and case where fasteners go and use OXY guard or other grounding paste to insure longevity of the connections to include engine chassis and body panel grounds. "your fender maybe grounded however; what are the grounds condition corroded rusted? if so clean them or go new.

If you are considering a rebuilt alt why not go to a 200 amp single wire Denso that is just bolt on no regulator needed. Any other alternator will require a skillset or fabricator to make brackets to fit the application.
 

FellowTraveler

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Ok so I have one that looks like it without the adjustable on the back. It's a "Standard VR125". Does anyone local sell the C8313 or is it an internet special?
They can be had on the bay for as little as $16.99 w/free shipping..........it will come trimmed to 14.7 volts, if you want to check the trim do so EXACTLY as shown in the video on a able. If out of spec do not rotate the adjuster trimmer more than a very little amount or you will destroy it.
 

Scholioso

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Reason for not going to the 1 wire 200 amp is the cost. That puppy is $380, whereas a rebuilt denso is $90. I can buy a lot of voltage regulators for that price. I will double check all grounds as well.

I just purchased a C8313 from ebay as you had said, should be here in 2 weeks which really kills me as I need it asap. I'm going to take the one I have back to oreillys & try to find a replacement for now. I'm moving & I really dont want to pay a towing bill. I'd rather just drive the truck...
 

FellowTraveler

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Reason for not going to the 1 wire 200 amp is the cost. That puppy is $380, whereas a rebuilt denso is $90. I can buy a lot of voltage regulators for that price. I will double check all grounds as well.

I just purchased a C8313 from ebay as you had said, should be here in 2 weeks which really kills me as I need it asap. I'm going to take the one I have back to oreillys & try to find a replacement for now. I'm moving & I really dont want to pay a towing bill. I'd rather just drive the truck...
Auto parts stores do not have any reference or listing to exactly what regulator to use for the Cummins conversions.....I had all the regulator issues too and remember the denso is controlled by a computer in the Ram Cummins application but I dug into researching what the problem actually was and found the fix.
 

Scholioso

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Problem is I'm not 100% sure I have the correct denso specific alternator. Didn't realize I was going to have such a problem with this. I think I'm going to order a Denso reman'd from RockAuto & install it just to be 100% sure. I don't feel like chasing these issues.
 

FellowTraveler

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Problem is I'm not 100% sure I have the correct denso specific alternator. Didn't realize I was going to have such a problem with this. I think I'm going to order a Denso reman'd from RockAuto & install it just to be 100% sure. I don't feel like chasing these issues.
The image you had posted is a denso alternator for the Cummins application......what problem? Just get the right regulator and be done with it.
 

FellowTraveler

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Look up a 90 d350 with a cummins. They came with a 120 amp nippendenso alternator and external voltage regulator.
Interesting, the part number he has been using is correct for his application and perhaps defective according to his mention that it does not produce 14.7 @ idle....and/or the alt too.
 
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Scholioso

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I went down to oreillys & measured all the regulators for an 89 d350 cummins. They all measured around 5.something ohms. Which tells me that my multimeter could be bad or low battery causing a false reading. Either way, I got the lowest reading one (master pro, go figure). Put it in the truck, same thing. Batteries are at 12.4 volts, start it up, it climbs up to 15.1 ish volts at idle. Doesn't really go anywhere from there. When going down the road, the voltage drops to around 13 to 14 volts. When ya shut the truck off, voltage drops to 12.5 again.

The reason I purchased another alternator was for a few reasons:
  1. the guy I got it off of was using it on his 1970 duster or something of that nature. Said he got it off of a dodge dakota?
  2. the main battery stud/lug on the back was shortened to fit on his engine. This really limited me on fitting a cable on the back, as I had to put nut, cable, nut. & tighten. It's hard to explain, I'll get a pic when the truck gets back from the exhaust shop.
  3. the alternator that came on the Cummins had a bigger backing case plate than the one I picked up. Reason I know this was I accidentally put the original cummins alt backing plate on this other alt I picked up & theres a pretty big gap all around the edges.
This is why I was asking how you knew what alternator it was FellowTraveler. I wasnt sure if the backing plate on the alternator was the identifier, because if so, it's wrong for this alternator. Anyways, new alt should be in today. Regulator should be here soon as well.

Truck limped down to the exhaust shop pretty well. Reason for limping is the dakota digital unit was faulty & I had to send it back, should be getting that back today. Then the trans controller will operate correctly!

Thanks for all of your help!
 

THEFERMANATOR

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15 volts when cold is fine. So long as it drops back to 13.5-14.5 volts after 15 minutes, its working like it should. Most regulators are set to run 14.5-15.8 volts for the 1st 10-15 minutes to quickly recover the bstteries charge, then drop back to a safe constant voltage(normally 13.5-14.2).
 

FellowTraveler

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As for identifying bad batteries I like to charge them to 100% and let them sit over a few days then measure the voltage. Also the battery case can have voltage present which can cause issues if so it needs to be cleaned and you must be careful not to get any of the cleaner "usually baking soda" into any of the battery cells because it will destroy the battery.
I went down to oreillys & measured all the regulators for an 89 d350 cummins. They all measured around 5.something ohms.
Did you set the meter as per the directions o the video I posted, or?
 

Scholioso

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As for identifying bad batteries I like to charge them to 100% and let them sit over a few days then measure the voltage. Also the battery case can have voltage present which can cause issues if so it needs to be cleaned and you must be careful not to get any of the cleaner "usually baking soda" into any of the battery cells because it will destroy the battery.


Did you set the meter as per the directions o the video I posted, or?
Yes sir! One thing I've learned from working on aircraft, gotta replicate exactly what the pilots are describing.
 
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