Help diagnose my Electrical over voltage issue..

[Hotshot]

Electrics are my fav part of Maintenance on cars, I know I知 weired.. but I知 stumped.

86 Targa 3.2 - I have full factory manuals and stock wiring, no funny biz. All terminals and group points shiny and non oxidized. All ceramic fuses.
JWest mod installed for Headlight relay.


A few months ago I was driving along and I noticed my 14.6 normal state was shooting up to 15.5. It was clipping the radio and turning it off ( new Blaupunkt SQR) and making my central locking light look possessed.

I noticed that with my gas pedal I can control the voltage, so I suspected the orig Volt Reg and Alt should get changed as 35 years is a long time.

- New Velo OEM ALTN/Volt reg installed. Ground straps all checked good.


All seemed ok then a day later problem came back.

Started to isolate circuits. Headlights, flashers, central locking, etc, and found my seat power motor didn稚 work / glitchy. Thought that motor is pulling too much and took the seat power off line.

Problem solved! Now 13.9-14.6 steady as a rock, day night, AC all good...THEN.


After 500 km since then, last night I知 driving home and I select the Vent blower at a light. So with idle power it shoots up. 14.0-15 and get erratic.

Light turns green, rpm increase ( 2500 when you should check n test ) it gets high and I decide to try the pax seat power motor, and Poof, radio clips, central lock light goes nutty.

Then I tried the heat blowers, fog lights, any other thing with lights and motors and it all did the same as I was close to home.


Any thoughts before I really dive into harnesses and ground points, and isolate each bloody circuit?

My battery is massive Merc Benz bat the PO installed. 2017 date on it. In winter I have it tendered. She cranks great, puts 12.7 volts tested at the Bat and with my voltmeter in the car resting.


I may try and swap bats.

[blucille]

Seems to me you got a defective replacement voltage regulator.

[Stophos]

Not exactly the same symptoms but I had a similar erratic problem years back and it was the ignition switch.

[Hotshot]

Originally Posted by blucille

Seems to me you got a defective replacement voltage regulator.

It has been stable as a rock until this issue.

[John W.]

Usually but not always bad grounds cause voltage dropouts not higher voltage. If that痴 the original alternator it痴 probably time to get it rebuilt at a local shop. New brushes, bearings and regulator. That cured my similar problem. Cost $110.

[Hotshot]

Originally Posted by John W.

Usually but not always bad grounds cause voltage dropouts not higher voltage. If that痴 the original alternator it痴 probably time to get it rebuilt at a local shop. New brushes, bearings and regulator. That cured my similar problem. Cost $110.

I replaced the Alternator. And the voltage reg. There one unit from Veleo. Porsche OEM.

Your right John, it would be a drop. An increase would be a pump / motor drawing more, which is why I def had the seat motor binding causing an issue.

But that circuit is totally offline.

I知 wondering if a Battery can be bad in the sense that when it needs to put out a little more load it acts up?

Since the fix, it痴 been 14.6 to 13.9 like a champ. So the new Alt/ Vr is working.

[Tea Tray]

Have you checked the wires to the alternator? Both ends? My memory is foggy about an alternator ground wire.

[Jdub]

A solid ground from your alternator includes the cable from the alternator to the top of the transmission, then from the transmission to the body, passenger side, and of course the battery as well. It is VERY easy to miss a compromised ground wire that has high resistance - even the uncoated strap can look fine until you look closely and find white dust throughout (that is, remove the covering and twist it about to see the buildup).

I would focus on this since it costs you nothing and had me on knees crying until I figured it out (fresh Valeo, cleaned ground point, etc.). My experience was flickering - you have real world numbers that mimic what I saw.

Good luck!

[darrin]

still think it's a defective alternator/vr -- a "new" Valero is, as I understand it, still a remanufactured unit, with the remanufacturing occurring in a 3rd world factory. If you continue to have intermittent issues after checking grounds/etc., I'd find a local, old school, alternator/generator rebuild shop and have the replacement alternator carefully examined/rebuilt - had similar problems with 3 different remanufactured alternator/vrs until I had a local shop go through, check and rebuild my existing unit.

[Hotshot]

Originally Posted by darrin

still think it's a defective alternator/vr -- a "new" Valero is, as I understand it, still a remanufactured unit, with the remanufacturing occurring in a 3rd world factory. If you continue to have intermittent issues after checking grounds/etc., I'd find a local, old school, alternator/generator rebuild shop and have the replacement alternator carefully examined/rebuilt - had similar problems with 3 different remanufactured alternator/vrs until I had a local shop go through, check and rebuild my existing unit.

Interesting. Mine was new. I could have opted for rebuild but this is a new one made in Europe. Although the VR is from China. Wasn稚 cheap.

What is killing me is that for 500km it was SPOT on and perfect before.

[Hotshot]

Originally Posted by Jdub

A solid ground from your alternator includes the cable from the alternator to the top of the transmission, then from the transmission to the body, passenger side, and of course the battery as well. It is VERY easy to miss a compromised ground wire that has high resistance - even the uncoated strap can look fine until you look closely and find white dust throughout (that is, remove the covering and twist it about to see the buildup).

I would focus on this since it costs you nothing and had me on knees crying until I figured it out (fresh Valeo, cleaned ground point, etc.). My experience was flickering - you have real world numbers that mimic what I saw.

Good luck!

Thx J Dub.

Are you referring to the grounding strap from Tranny to Block underneath.
? As in the flat fat breaded one?

[Jdub]

Yes, the flat band grounding strap that is braided. If it is old do yourself a favor and replace it. The alternator ground wire the same, and I well remember pulling the plastic off the battery ground strap, twisting it, and watching the corroded white powder . I do this as a precaution but then learned this courtesy of British Leyland

[spoke]

Originally Posted by Hotshot

A few months ago I was driving along and I noticed my 14.6 normal state was shooting up to 15.5.

New Velo OEM ALTN/Volt reg installed. Ground straps all checked good.

All seemed ok then a day later problem came back.

Started to isolate circuits. Headlights, flashers, central locking, etc, and found my seat power motor didn’t work / glitchy. Thought that motor is pulling too much and took the seat power off line.

Problem solved! Now 13.9-14.6 steady as a rock, day night, AC all good...THEN.


After 500 km since then, last night I’m driving home and I select the Vent blower at a light. So with idle power it shoots up. 14.0-15 and get erratic.

I would think that any voltage above 14.0V is too high. 14.6V seems high to me. May be ok but seems high.

So you change the alternator/VR and get the same result? That points to the original Alt/VR are ok. Can you/Did you have the original Alt/VR checked at Autozone or whoever does that kind of testing?

Seems something other than your Alt/VR is at issue. Keep in mind that the alternator is a big inductor. If the connection to the alternator (inductor) is interrupted the alternator will react by spiking high. It would be interesting to get an oscilloscope on the battery voltage to see the actual waveform.

You like electrical work so if you don't have an oscilloscope you might want to consider buying one.

Here's an oscilloscope front end that plugs into a laptop USB port. We use this one at work.

https://www.newark.com/velleman-sa/pcsu1000/2-channel-usb-pc-oscilloscope/dp/60AC5903?mckv=s0tW4W6cR_dc|pcrid||plid||kword||mat ch|e|slid||product|60AC5903|pgrid|1234751786630905 |ptaid|pla-4580771609217368|&msclkid=3246b717d0e614a8a507d65f2c02c542&CMP=KNC-BUSA-GEN-Shopping-NewStructure-Verylow

I'll bet you have high voltage spikes on the "battery" voltage. Keep in mind that a DC voltmeter averages the voltage seen at the terminals measured.

One test would be to grab another battery and try it out. If you have a battery handy or another car, this would be an easy way to discount the battery as the issue. I had a battery that was failing and I couldn't get 13V while running. Thought it was the alt/VR. Changed the battery and got solid 14.0V.

[Hotshot]

Very good idea. I am going to do both those things when I get back. I値l check out that scope. I do want one.