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6.5 to 5.9 Cummins Alternator Help

Scholioso said:
Are these problems only related to the denso alternator?
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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.
 
Scholioso said:
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?
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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.
 
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...
 
Scholioso said:
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...
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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.
 
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.
 
Scholioso said:
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.
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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.
 
THEFERMANATOR said:
Look up a 90 d350 with a cummins. They came with a 120 amp nippendenso alternator and external voltage regulator.
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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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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!
 
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).
 
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.
Scholioso said:
I went down to oreillys & measured all the regulators for an 89 d350 cummins. They all measured around 5.something ohms.
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Did you set the meter as per the directions o the video I posted, or?
 
FellowTraveler said:
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?
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Yes sir! One thing I've learned from working on aircraft, gotta replicate exactly what the pilots are describing.
 
Ok. So I got a new denso alternator & the heavy duty voltage regulator. The truck lights are all flickering & very bright. It's at 15 volts after start, then drops to 13-14 when running. Headlights, instrument cluster, etc. All kinda flicker or pulse I guess is a better word. Ideas? Usually when this happens, it's my understanding that it's the voltage regulator. Both regulators (oreillys & the c8313) do this. Ideas?
 
A. Regulator bad (new parts dont mean good parts)
B. Wiring to regulator bad
C. Alternator bad

Building custom work trucks, we often had to do multiple alternator set up. When doing adaptive work there was a local alternator/ starter rebuild shop that I paid extra to have then build an alternator to the specific task.

Nowdays that is so much easier done through powermaster. That would be my desire in your situation. however I cant afford 1/2 the desires for my current build, so... yeah.
 
I had the alternator tested, it's good. The voltage regulator is reading according to the video FellowTraveller posted. I guess that just leaves my wiring. Could it be possible that the two small wires on the alt need to be swapped? Otherwise I wired it up according to how everyone specifies.
 
FellowTraveler said:
Ground the regulator to the alternator case making sure its a clean connection on both ends.
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Ok I will try that. It's just weird how the alternator case is grounded directly to the battery & the regulator is as well. I thought this would be better. Maybe due to this, the regulator isn't completing its circuit as it's just returning straight to the battery? I will report back with my findings.

Also, online there are varying ways of where the ignition wire actually connects. I wired it up similar to this. But instead of ignition leading straight to the connection itself, I "Y"-d it in with the wire from the alternator which leads to the regulator. Not sure if that makes a difference either.
 

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Sand said:
Mine is pulsing. Headlights and dash lights. You can hear it at idle too. It's because the regulator is not getting a clean power reading from the battery. I spurred off another subsystem for ignition switched power to the regulator an it's not happy. If I jump a wire from the battery direct to the regulator it smooths out. I need to run a nice relay switched power supply from the battery direct to the regulator.
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I just noticed this. I was rereading the posts. My truck is doing the same. I haven't tried jumping power from the battery to the regulator tho. So you're thinking of running an ignition relay to trigger straight battery power to the regulator? Please let me know how this works out!
 
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