My vehicle electrical system voltage is surging.
It seems almost unnoticible at idle sometimes.
1800 rpm and above it's very noticible.Anyone else had this problem.
My lights are being affected and who knows what else. I checked the voltage at the battery with the engine running and 14.5 to 15 volts is the fluctuation with an analog meter.
I don't want to foul up any of the computers so I haven't been using it.
Is it the alternator or the BCM?
Does the BCM regulate alternator output?
Could it be a bad diode in the alternator?

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2005 Limited CRD
GDE Hot tune, Airtex Lift pump, Filter head,ProVent, 255/65/17 Kumho KL78
other diesels :
2001 Dodge 4x4 24 valve 510/1050 @rear wheels
1984 Mitsubishi Turbo Diesel_gone but not forgotten

The voltage regulator is part of the PCM(ECM for CRD) in a KJ.Could be a bad wire,check those 1st.After that it's off to the dealership as the only way to correctly diagnose/test the system is to use the DRBIII/Starscan.

As stated..the voltage is regulated by the ECM.
I would suggest that you disconnect the battery and re-plug the connectors on the ECM.
The alternator has a clutch fitted inside the drive pulley which is prone to failure so check that this clutch is not causing the speed of the alternator to fluctuate and check that the serpentine belt, idlers and tensioner pulley are working as they should.

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2002 Export CRD 2.5 Sport

X2 on that decoupler/clutch. Check is to idle the vehicle in Park, stand at front driver's side of the fender, look down along the serp belt to the tensioner way down in there, if it's bouncing around the decoupler is bad, also look at front of idler pulleys for leaking grease. If the decoupler is bad it's an $80 or so item that can be replaced although removal requires a special tool unless someone knows another way. If you replace the decoupler don't go for a cheap generic best get a CRD specific one that's able to handle the diesel 4cylinder power cycle.

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Sold to LOST member my 05 Ltd, GDE Stg II turbo + TCM tune, SunCoast TC w. Transgo kit, Steiger window regulators, Samcos, Fumoto valve, 2nd gen filter head with Lub. Spec. bleeder, Hayden clutch & 11 blade fan, inverted spare, P-1 battery, BF Goodrich Long Trail TAs, Etecno1 glow plugs, timing belt at 50K miles/8 yrs

it is the clutch / pulley , my 06 did that same thing until I replaced the alt and pulley

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05 liberty CRD Limited - suncoast TC , GDE Turbo , GDE TCM Tune 2gen OEM filter head, stant 195 tsat, Autoandart Window Fix, New TB kit ~190k (Geordi)
06 Liberty CRD Limited - stant 195 tstat Autoandart Window Fix, 2gen OEM filter head, New TB kit ~180k (Geordi), GDE Turbo, GDE TCM ECO tune

Just an update. New pulley solved the problem. No tool needed to remove the old pulley. Just a 10m socket and a vice on the old pulley.
Thanks guys

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2005 Limited CRD
GDE Hot tune, Airtex Lift pump, Filter head,ProVent, 255/65/17 Kumho KL78
other diesels :
2001 Dodge 4x4 24 valve 510/1050 @rear wheels
1984 Mitsubishi Turbo Diesel_gone but not forgotten