P38A P38 diesel 2001, overcharging / alternator recommendation

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H

Hellenes

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Location
Forde, Norway
Half a year ago I fitted a DELCO REMY DRA3673 alternator due to charge voltage variations (from too low to 16V). The new alternator worked well for half a year but then started to charge with up to 18V, also at low rpm.
The cabling between the alternator and battery is upgraded. The voltage regulator is also replaced with no improvement.
Any advise for further troubleshooting?
Any experience to share with alternators for P38 diesel? Is the original capacity to low? (No extra consumers added to the car). What type of alternator do you recommend as a replacement or upgrade?
 
Original alternator was for older type batteries with lower voltage required. I’d recommend a BMW alternator (standard for M51 but cheaper than LR)
If you have a modern calcium battery fitted id go with a non standard voltage regulator with a 14.7v setpoint. They are about £14 and ten minutes to change with basic tools. The guys can show you which one to get
 
Check the earth strap from chassis to engine, it's often the cause of alternator output appearing to fluctuate. As a test you can put a jump lead from the alternator case to the battery negative.
 
Earth strap OK. I've tested with a jump lead but no improvement.
Also attached an oscilloscope and only stable continuous pulses detected.
I'll do some more testing over the weekend, to be continued.
 
Hellenes said:
Earth strap OK. I've tested with a jump lead but no improvement.
Also attached an oscilloscope and only stable continuous pulses detected.
I'll do some more testing over the weekend, to be continued.
Click to expand...
Sounds like the diode pack has given up if there are no high resistance connections in either the positive or negative sides. You can see ripple but I would not expect to see defined pulses if the battery is properly connected as the battery damps out any pulse effect. Try a jumper from the alternator positive output to the battery, the positive cable has been known to corrode inside the plastic sleeve.
 
Jumper from alternator positive is in place in parallel with the original wiring.
I presume there will always be pulses, although low ones. I'll check what range we used on the oscilloscope. Thought I would see irregular pulses if a diode was broken. I'll check the diodes with a multimeter.
I can't imagine the signal coming from the dash charge light / BECM to the alternator can influence the charging? Or if any, feedback from the battery to the BECM?
 
Hellenes said:
Jumper from alternator positive is in place in parallel with the original wiring.
I presume there will always be pulses, although low ones. I'll check what range we used on the oscilloscope. Thought I would see irregular pulses if a diode was broken. I'll check the diodes with a multimeter.
I can't imagine the signal coming from the dash charge light / BECM to the alternator can influence the charging? Or if any, feedback from the battery to the BECM?
Click to expand...
The charge light/BECM circuit to D+ has no effect once charging has started. With a scope on 5volts per division, you should see about 14 volts with some ripple on the trace. The amount of ripple varies but should not if I remember correctly be more than 1 volt if that. with a single diode out of 6 failed you will only see a brief dip greater than the ripple.
 
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