W108 4.5 voltage regulator issue - Mercedes-Benz Forum

Reply
 
LinkBack Thread Tools Display Modes
post #1 of 15 (permalink) Old 07-08-2016, 01:17 PM Thread Starter
BenzWorld Member
 
TZ_280SEL's Avatar
 
Date registered: Feb 2010
Vehicle: 1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
Location: Williamsburg, VA
Posts: 322
Mentioned: 3 Post(s)
Quoted: 39 Post(s)
(Thread Starter)
W108 4.5 voltage regulator issue

Now that I have an actual voltage indication (via my megasquirt), I have discovered a strange issue. Periodically, the voltage on the system will spike from the normal 13.5 volts to 15-16volts. It will stay there for a second or two and then return. It does this randomly and it is an actual voltage transient as it is accompanied by a change in headlight brightness and engine sound.

Alternator is only 15,000 miles old. I swapped the voltage regulator with a new one I had purchased a while back....same story.

I am assuming there is a momentary open in the sensing line to the battery. Is this a valid assumption? Not sure what else could be causing my issue.

Any thoughts?
TZ_280SEL is offline  
Sponsored Links
Advertisement
 
post #2 of 15 (permalink) Old 07-08-2016, 04:20 PM
w108,107 Parts Hoarder
 
Fonzi's Avatar
 
Date registered: Jun 2010
Vehicle: 4Keep:450slc5.0cab 280sl5sp 280se4.5 500seAMG 2sell:500sl92 380se83 300se86 350sl4sp 75slc MorInSig
Location: Philadelphia Area
Posts: 19,273
Mentioned: 29 Post(s)
Quoted: 1717 Post(s)
Lifetime Premium Member
Garage
I don't know, but I know my 4.5 needs a new voltage regulator. The low beams both blew when I hit a bump in the road and and my old battery old battery was bubbling. That's when I decided to take a look at the colts. Hmm... Steady ~16+volts. Yikes!

.

My signature:
Click for list of my 34 MB since 2010. If, you want 70's-80's Mercedes tuner wheels, let me know.
Fonzi is offline  
post #3 of 15 (permalink) Old 07-11-2016, 12:36 PM
BenzWorld Elite
 
Grubeguy's Avatar
 
Date registered: Jan 2006
Vehicle: 73 280SE 4.5, 71 300SEL, 03 BMW Z4, 72 Fiat 850, 80 Triumph TR7, 85 Porsche 911
Location: DC Area
Posts: 2,128
Mentioned: 1 Post(s)
Quoted: 102 Post(s)
Send a message via MSN to Grubeguy Send a message via Yahoo to Grubeguy
Aren't the regulators internal to the alternator these days? My previous searches for separate regulators came up with zilch ...
Grubeguy is offline  
 
post #4 of 15 (permalink) Old 07-11-2016, 01:44 PM
w108,107 Parts Hoarder
 
Fonzi's Avatar
 
Date registered: Jun 2010
Vehicle: 4Keep:450slc5.0cab 280sl5sp 280se4.5 500seAMG 2sell:500sl92 380se83 300se86 350sl4sp 75slc MorInSig
Location: Philadelphia Area
Posts: 19,273
Mentioned: 29 Post(s)
Quoted: 1717 Post(s)
Lifetime Premium Member
Garage
Quote:
Originally Posted by Grubeguy View Post
Aren't the regulators internal to the alternator these days? My previous searches for separate regulators came up with zilch ...
These days, and even in the later 70's 4.5 motors, but not the w108 4.5 which are the equivalent to the 4.5 in the early North American R/c107. These have external voltage regulators. On the w108 it is right behind the d-jet ECU on the passenger side (as I believe all 4.5 w108 are North American models, perhaps developed to meet emissions standards, as the 3.5 is actually more powerful).

You can tell the difference in the 4.5 alternators based on the plug on the back apparently. I sent all the 4.5 alternators I had to @rockcrusher in a flat rate box a few months ago. Perhaps he could have more details if needed.

.

My signature:
Click for list of my 34 MB since 2010. If, you want 70's-80's Mercedes tuner wheels, let me know.
Fonzi is offline  
post #5 of 15 (permalink) Old 07-12-2016, 05:47 AM Thread Starter
BenzWorld Member
 
TZ_280SEL's Avatar
 
Date registered: Feb 2010
Vehicle: 1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
Location: Williamsburg, VA
Posts: 322
Mentioned: 3 Post(s)
Quoted: 39 Post(s)
(Thread Starter)
So, problem solved. It is actually the alternator which is bad, but not for the normal reasons. The plug on the back of the alternator is held in place by a couple of plastic tabs, or should I say it is supposed to be held in place by a couple of tabs. My plug is being held in place by force of habit, which is not strong enough apparently.

When you wiggle the plug, voltage will spike to about 16-17v and then you wiggle it again and it comes back to 13.5v.

I did make a new harness from the alternator to the regulator as the old one was pretty beat up. All three wires into the alternator had their insulation broken from fatigue at the connector. One of them only had about a third of the copper strands left in tact.

So, alternator on order, new regulator, new harness....hopefully case closed.
rumb likes this.
TZ_280SEL is offline  
post #6 of 15 (permalink) Old 01-03-2017, 02:26 PM
Premium Member
 
Droidster's Avatar
 
Date registered: Nov 2013
Vehicle: 74 450SL 107 044 12 020684 73 280SE 4.5 108 067 12 021470
Location: Los Angeles, CA
Posts: 884
Mentioned: 7 Post(s)
Quoted: 174 Post(s)
Premium Member
Quote:
Originally Posted by TZ_280SEL View Post
So, problem solved. It is actually the alternator which is bad, but not for the normal reasons. The plug on the back of the alternator is held in place by a couple of plastic tabs, or should I say it is supposed to be held in place by a couple of tabs. My plug is being held in place by force of habit, which is not strong enough apparently.

When you wiggle the plug, voltage will spike to about 16-17v and then you wiggle it again and it comes back to 13.5v.

I did make a new harness from the alternator to the regulator as the old one was pretty beat up. All three wires into the alternator had their insulation broken from fatigue at the connector. One of them only had about a third of the copper strands left in tact.

So, alternator on order, new regulator, new harness....hopefully case closed.
My battery recently died, I recharged it and checked the voltage with my multimeter and it was jumping all over the place. I suspected my voltage regulator and a new one is on its way, but just found this thread. I'll check the plug on the alternator as well.

Just curious, after replacing those parts, has it solved your issue?

Droidster is online now  
post #7 of 15 (permalink) Old 01-03-2017, 02:57 PM Thread Starter
BenzWorld Member
 
TZ_280SEL's Avatar
 
Date registered: Feb 2010
Vehicle: 1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
Location: Williamsburg, VA
Posts: 322
Mentioned: 3 Post(s)
Quoted: 39 Post(s)
(Thread Starter)
Yes, after replacing the alternator, my issue is solved.
TZ_280SEL is offline  
post #8 of 15 (permalink) Old 01-03-2017, 03:12 PM
Premium Member
 
Droidster's Avatar
 
Date registered: Nov 2013
Vehicle: 74 450SL 107 044 12 020684 73 280SE 4.5 108 067 12 021470
Location: Los Angeles, CA
Posts: 884
Mentioned: 7 Post(s)
Quoted: 174 Post(s)
Premium Member
Quote:
Originally Posted by TZ_280SEL View Post
Yes, after replacing the alternator, my issue is solved.
Good to know, thanks so much!
Droidster is online now  
post #9 of 15 (permalink) Old 01-03-2017, 05:44 PM
w108,107 Parts Hoarder
 
Fonzi's Avatar
 
Date registered: Jun 2010
Vehicle: 4Keep:450slc5.0cab 280sl5sp 280se4.5 500seAMG 2sell:500sl92 380se83 300se86 350sl4sp 75slc MorInSig
Location: Philadelphia Area
Posts: 19,273
Mentioned: 29 Post(s)
Quoted: 1717 Post(s)
Lifetime Premium Member
Garage
W108 4.5 voltage regulator issue

I had two electrical issues on my w108. First the insulator on the bracket that holds the wire from the battery to the starter failed. Then the metal of the bracket chewed through the insulation on the wire. That's when I got huge sparks, and whole bunch of the insulation melted off the wire. It's interesting how sparks and fire under the hood can be such a bad thing.

As a temporary solution (after disconnecting the battery), I wrapped the wire in duct tape until I could replace the starter wire.

Then one day I was driving in some very cold weather on a very bumpy road. Both headlights went out at the same time. Then I popped the hood in my driveway to take a look and I heard the battery boiling. I was running around 17-18 volts. I disconnected the wires on the alternator until I could get to the voltage regulator issue. Replacing the external voltage regulator solved the problem.

That's the way I remeber it anyway.

.

My signature:
Click for list of my 34 MB since 2010. If, you want 70's-80's Mercedes tuner wheels, let me know.
Fonzi is offline  
post #10 of 15 (permalink) Old 01-03-2017, 06:10 PM
Premium Member
 
Droidster's Avatar
 
Date registered: Nov 2013
Vehicle: 74 450SL 107 044 12 020684 73 280SE 4.5 108 067 12 021470
Location: Los Angeles, CA
Posts: 884
Mentioned: 7 Post(s)
Quoted: 174 Post(s)
Premium Member
Quote:
Originally Posted by Fonzi View Post
I had two electrical issues on my w108. First the insulator on the bracket that holds the wire from the battery to the starter failed. Then the metal of the bracket chewed through the insulation on the wire. That's when I got huge sparks, and whole bunch of the insulation melted off the wire. It's interesting how sparks and fire under the hood can be such a bad thing.

As a temporary solution (after disconnecting the battery), I wrapped the wire in duct tape until I could replace the starter wire.

Then one day I was driving in some very cold weather on a very bumpy road. Both headlights went out at the same time. Then I popped the hood in my driveway to take a look and I heard the battery boiling. I was running around 17-18 volts. I disconnected the wires on the alternator until I could get to the voltage regulator issue. Replacing the external voltage regulator solved the problem.

That's the way I remeber it anyway.
:flushed::flushed::flushed:

Thanks for the reminder. I'll be checking the harness as well as I've seen some insulation that has degraded.
Droidster is online now  
Sponsored Links
Advertisement
 
Reply

  Mercedes-Benz Forum > General Mercedes-Benz Forums > Vintage Mercedes-Benz

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Mercedes-Benz Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











  • Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
     
    Thread Tools
    Show Printable Version Show Printable Version
    Email this Page Email this Page
    Display Modes
    Linear Mode Linear Mode



    Posting Rules  
    You may post new threads
    You may post replies
    You may not post attachments
    You may not edit your posts

    BB code is On
    Smilies are On
    [IMG] code is On
    HTML code is Off
    Trackbacks are On
    Pingbacks are On
    Refbacks are On

     

    Title goes here

    close
    video goes here
    description goes here. Read Full Story
    For the best viewing experience please update your browser to Google Chrome