Rhythmic pulsing of voltmeter

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sargentrs

sargentrs

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Having a weird thing happening recently. I installed a Sunpro voltmeter a couple of months ago and things have been running well. Since I bypassed my original ignition and installed the HEI ignition module setup, she's been getting a good 13.5v at idle and 14.5 volts at rpms higher than 700 rpm. For the past couple of weeks, I've noticed a "rhythmic pulsing" of the voltmeter ranging between 13.5 and 14.5 volts at idle. Regular and consistent, up and down, up and down, up and down, in time with the revolutions of the engine. About every 1 second, so about 10 revolutions of the engine at 600 rpm, it'll drop down to 13.5 and then back up to 14.5. I can hear the engine idling accordingly and I even have an annoying vibration in my dash somewhere that keeps time with it as well. I know my P/S pump is leaking and occasionally whines and you can hear the whine keeping time with the voltmeter and the rattle in the dash. Could the P/S pump be dragging on the engine causing a pulsing of the alternator and affecting the revolutions of the alternator pulley causing the change in voltage. Or would some load on the voltage be causing the engine to revolve in that manner? The higher the rpm, the faster the rhythm of the voltmeter needle until I reach around 1500-2000 rpm then I guess the engine is turning faster than the pulsing and she holds a constant 14.5v. Before I start throwing $$ and parts at it, anybody experience this type of situation before?
 
Something could be loading the electrical system, causing the drop in voltage, and the load through the alternator will put a drag on the engine.

What electrical system mods have you done besides the HEI? Any big stereo? (Are you playing the 'death march' on it with its slow cadence? LOL) Are you running the heater blower or wiprers when this happens? (Just trying to think of big or rythmic loads)

Someone here had a similar issue with erratic charging voltage when he modded the wiring and took the alterantor output direct to the battery. It was fixed when he moved the alternator output connection to the big lug on the starter relay.
 
Could be the regulator or battery also. (just covering the bases) :)
 
The wiring on this beast is in such poor shape I've done everything I can to remove the load on the original wiring. To start with the bulkhead was fried so I did the madelectrical bypass. That cured my intermittent starting problem but was still only getting 12v at idle and 10+ with lights and heater. Over 800 rpms and I'd get 14+ but when I slowed down I lost charging voltage. Did the alternator to starter relay mod and was able to get 14+ and 12.5v at idle. Had an intermittent problem with the ignition harness so did the HEI module install and finally achieved 13v+ at idle 14.5v at any rpm above idle. All was good for a month and now this starts. Oddly, in gear at a red light, it's a rock steady 14v+ until I touch the gas then the pulsing starts. I'm leaning toward the VR myself. Saving up for a Denso internally regulated alternator so I can eliminate that circuit too. Before I'm done the only original wiring in the engine compartment is going to be the headlights and I'm seriously considering wiring those in with relays for 12v to the lights. Lights flicker badly at anything below 1200 rpm-ish.
 
Btw, added a 20w amp to boost my phone's mp3, was fine until now, and a 3 pc Sunpro gauge set, that's it. Wipers/heater doesn't affect it one way or another but blinkers drop it 2v every time they blink and always have before I changed anything.
 
my truck surges at first after a cold start with headlights on and heater

i just assume my voltage regulator is going out, stock one from 92

after 5 min or less tho it stops and sits at 13 volts is steady

i think its just charging the battery and is acting dumb and old
 
When flickering at certain rpm's and voltages going down at idle and when accesories or any other device that draws power comes on, the regulator tries to make up for it by increasing the field voltage to the alternator.
At idle there are not sufficient rpm's for the alternator to put any more power out than it does, so some of the load comes off the battery. (lights dim and signals slow down)
In doing all this the regulator will vary the voltage output of the alternator if it gets too high and we see that on/off effect of the regulator in the lights and volt or amp meter because it is the most obvious there.
The only way we can get away from that is to make the amp draw at idle low enough as to not require the added voltage from the alternator.

Good wiring is a really good start, and we have all seen the benefits of relays being used so that the main power draw of lights and such is not run through 10 feet of wire and a switch before it gets to it's intended home in the bulb.
By then the voltage and amps are already severly degraded.

Two very easy things that can help right away is a change to LED type lighting.
Your average brake lights use about 6 amps of power, and the same amount of LED's use about 1/4 amps (.025)amps
That leaves about 5 and 3/4 more amps for the headlights (or anything else) to use at idle and it makes a big difference.

One other easy one is an electronic flasher for the signals.
Electronic flashers don't use amps to heat a metal strip to make it bend to make and break the contact.
Signals that flash slow at idle do so specifically because the voltage needed to heat the little metal strip is lower at idle and so it takes longer to open and close the contacts.
Electronic flashers flash the same speed all the time and draw way less amps doing it.

Doing just those two things will take about 10 amps off your charging system and battery at idle and it makes a big difference.

Wipers will barely slow at idle, and signals wont slow at all.
Now that I think about it turning my heater blower on high makes no difference in the wipers, lights, or signals at idle.
Stepping on the brakes has zero effect on the headlights either since the amp draw to light them is so small with LED's
 
My experience,, the condition described was the regulator in numerous examples.
So often that I'll plug in a known good regulator as a first step in diagnoses of rhythmic pulse.
 
RedFish said:
My experience,, the condition described was the regulator in numerous examples.
So often that I'll plug in a known good regulator as a first step in diagnoses of rhythmic pulse.
Click to expand...

I agree, and that would need to be fixed anyway.
My post was intended more for after the regulator fix, but doing the lights and flasher before or after doesn't matter.
(well unless the current spiked and killed brand new LED's, but that is doubtful)
 
Is that mechanical or IC? O'reillys also had one for 17.99 but it didn't specify whether it was mechanical or IC so I'm assuming it's mechanical. The 17.99 and the 22.99 were both BWD and the IC version was AC/Delco. I like Duralast too. Don't guess there's any big difference or pros/cons on the IC version vs the mechanical version so probably go with that Duralast. Thanks!
 
Neither of the ones you have linked are mechanical; they are both electronic. The older mechanical ones were not used in your vintage of charging system, and look quite different and connect with discrete wires, not a molded plug. Finding the most reliable and consistent is you goal here; BWD is a line from Standard Motor Products; they are probably all made in Mexico. (A older NOS Mopar unit might be US made.)
 
Sure thing! Apparently '70-'73 is different than '74-'76? Guy on ebay has a box full (about 60 NOS @ $25 ea) he says are '70-'73 but the model number is different than the high priced one's I've seen for '74-'76 ($75-$95).
 
I've spent the last 4 hours scouring the web for a voltage regulator made in America that was not NOS. Sadly, I don't think they exist anymore. At least, if they do, they don't say so. I found a thread regarding the AC Delco C603Z on a Mopar forum that said "Made in USA" stamped right on the part. However, when I search local parts sites for the C603Z, the pictures they show do not have the same stamping. I read of positive remarks regarding the SMP VR125 but can't confirm "made in USA" status. Everything I've read says that Wells was the original manufacturer of many of the Chrysler VRs but I can't confirm they are still made here. The most encouraging thing I've found was a Mopar Performance PN 3438150 at http://www.summitracing.com/parts/dcc-4529794/applications However, the application says it's for '70-'73 6 cylinder or '71-'82 SB/BB engines. The '74-'76 6 cylinder specs out the 3755960 which I have been unable to find, except $90 NOS. What's the difference in the 3438150 and the 3755960? They look identical. I realize this is just a lot of trouble to go to select a $30 VR but I don't have a lot else to do tonight and it's rather interesting to try to find one.
 
Can't tell you for sure. I do believe they are completely interchangeable. Could easily be the same part made for Chrysler but from a different vendor. BTW, I do indeed recall pulling, tossing, and replacing the original VR's several times 'back in the day', so the original units are by no means bulletproof!

Happy New Year!
 
So, did some searching related to the SMP VR125 and from what I can tell, it's a suitable replacement for either. According to the RockAuto catalog info..

Alternate/OEM Part Number(s): 1119180, 12336870, 12338616, 3438150, 3755850, 3755960, 4091050, 4111990, 4379100, 4379225, 5234625, C603, C603Z, C604, GRC395, GRC538

So I'm going to go ahead and get the Mopar Performance 3438150. At least it says Mopar on it. Thanks to all for the help and info!
 
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