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91 Loyale SPFI Pulsing Voltage "intermittent"


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8 replies to this topic

#1 Subeast-EA81

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Posted 12 December 2012 - 11:59 AM

So heres the story, My car has this pulsating voltage, 12-14 volt sweep at half second intervals. readings are on an after-market gauge, and as well as factory(makes my headlights look like a cop car so thats the only bonus:brow:). I checked it with my Fluke 289, didnt see any AC voltage, so the diodes in the Alternator must be working. I know its charging due to the amount of off-road lights i have on the car (4x @ 130watts). So heres were it gets whacky, when lugging along in 3rd gear <2000RPMs i can feel the varying voltage affecting the speed of the car (same fluctuation coincides with accel and decel with level throttle input. The best part is that its inconsistent, sometimes its doing it, which makes the car behave as described, and not doing it which lends to level voltage and smooth behavior.

Checked, done so far: Install Optima Blue top Marine Deep cycle Battery, replace clamp style battery cables with marine 4 awg cables with lug and screw down terminals soldered at both ends, Install block to chassis ground cable, cleaned and fix bad connections at alternator.

Being a Marine electrician for a living, usualy i can find the root issue myself, however the wonder wagon is challenging me again.

Any ideas? Discuss!

#2 Dee2

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Posted 12 December 2012 - 02:35 PM

I did a quick search on google for "car has this pulsating voltage" and found many answers basically summed up here:

http://www.ehow.com/...es-pulsing.html

#3 Subeast-EA81

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Posted 12 December 2012 - 03:57 PM

thanks for the link, i have addressed most of those concerns, other then a more in depth look at the voltage regulator. I assumed it was good as i didnt see any AC voltage coming from the alternator, i may be wrong

#4 Dee2

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Posted 12 December 2012 - 06:36 PM

The auto parts stores can usually do a free diagnostics check for you. Try more than one store if the attendant isn't experienced or you want a second opinion.

#5 Cougar

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Posted 12 December 2012 - 09:16 PM

If you haven't cleaned the battery connections yet then do that. You also might try clipping on a heavy ground wire between the alternator body and the negative battery lead to see if there is a problem there. Clean the chassis grounding wires also. Another thing you could try is disconnecting the main output lead at the alternator and see if you still see the voltage ramping up on the output stud. Be careful with the wire end, as you most likely already know that wire is hot at all times, so keep it isolated. If the voltage is still changing then it would seem to me the internal voltage regulator has a problem. There could be an issue with the brushes also since the trouble seems to be related to the RPMs.

My compliments to you on having such a fine piece of test equipment as the FLUKE 289 DVM. You are correct about the AC voltage. You should normally never see anything above .1 volt while the engine is running. Less is best in this case.

Edited by Cougar, 12 December 2012 - 09:25 PM.


#6 Subeast-EA81

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Posted 12 December 2012 - 11:00 PM

Well the majority of the checks and fixes lead me to think its time to take it to the bench and disassemble. or retrofit the CAT 150 amp alternator i have been kicking around since it was new. If i end up wedging the cat one in there, i'll have to post up pics, ill try disassembling the one thats in there and fiddling with it first as thats how i operate.

The 289 has been a good meter for sure, supose if i wanted to be realy nerdy i could use the 434 and check the waveform, but thats over kill :Flame:

#7 naru

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Posted 13 December 2012 - 09:21 AM

My compliments to you on having such a fine piece of test equipment as the FLUKE 289 DVM.


Big waste of money unless name dropping is a big part of your game,IMO.
My $10 meters do the same thing for $500 less.

#8 naru

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Posted 13 December 2012 - 09:37 AM

So heres the story, My car has this pulsating voltage, 12-14 volt sweep at half second intervals. readings are on an after-market gauge, and as well as factory(makes my headlights look like a cop car so thats the only bonus:brow:). I checked it with my Fluke 289, didnt see any AC voltage, so the diodes in the Alternator must be working. I know its charging due to the amount of off-road lights i have on the car (4x @ 130watts). So heres were it gets whacky, when lugging along in 3rd gear <2000RPMs i can feel the varying voltage affecting the speed of the car (same fluctuation coincides with accel and decel with level throttle input. The best part is that its inconsistent, sometimes its doing it, which makes the car behave as described, and not doing it which lends to level voltage and smooth behavior.

Checked, done so far: Install Optima Blue top Marine Deep cycle Battery, replace clamp style battery cables with marine 4 awg cables with lug and screw down terminals soldered at both ends, Install block to chassis ground cable, cleaned and fix bad connections at alternator.

Being a Marine electrician for a living, usualy i can find the root issue myself, however the wonder wagon is challenging me again.

Any ideas? Discuss!


Voltage regulator is in a slow cycling feedback loop because the alternator cannot maintain system voltage at lowish rpms w/o maximium field current.

Time for new brushes or less driving lights.

Absence of AC voltage coming from the alternator does not mean the regulator is good.

Exact reason for slowness of the cycle is interesting,but,very likely irrelevant. ....Or maybe not.

Edited by naru, 14 December 2012 - 10:49 AM.
maximium field current.


#9 Petersubaru

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Posted 15 December 2012 - 03:35 PM

thanks for the link, i have addressed most of those concerns, other then a more in depth look at the voltage regulator. I assumed it was good as i didnt see any AC voltage coming from the alternator, i may be wrong

..if you google this problem you will see that thousands of people have this same problem..I suppose that the regulators are somewhat tired and can go on like this for a very long time..I say this because almost every rebuilt alternator still has the original regulator that came with it when first new..both my original loyale and now my '01 subi pulsate ..even the replaced rebuilt upgraded nissan 100 amp does it and I have had to run the fuel pump directly from the battery by relay from the ecu to avoid hearing the fuel pump fluctuate..next time it will be a completely new alt for me that will have a new regulator installed..




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