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  #1  
Old 09-27-2010, 07:34 PM
muleears's Avatar
Old MB Driver
 
Join Date: May 2006
Location: Windsor, VA
Posts: 1,435
Alternator/charging system question

The battery was too weak to start my son's '85 123 the other day. I put it on a charger and brought it back. I had no warning lights about a charging problem. I checked the charging system with a little tester I got from Harbor Freight. It says the system is not charging. I then replaced the voltage reg. in the alternator, hoping that was the problem. The little tester still says its not charging. When I put the new voltage reg. in, does it take a certain amount of time for the brushes to seat and begin charging? Or should it work properly right away?

I guess I'll take it to Advance and let them test it and see what their machine says.

I still have no warning light about the charging system. The light comes on when I turn the key so I know it works.

I have a multimeter, can I check the system myself?

__________________

Muleears
'07 E320 Bluetec 133K my DD
'04 Jaguar XJ8 VDP, 34K
'10 Hyundai Accent 60K Grocery Getter
'02 VW Golf soon to be on the road again
'97 E300 Diesel Son's DD
'61 VERY tolerant wife

Hampton Roads, VA USA

Gone but not forgotten:
'67 250S 95K
'86 300SDL
'87 300D Turbo, 364K! R.I.P.
'98 E300 Turbodiesel, 213K
'02 S420, 164K
'01 Prius 138K
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  #2  
Old 09-27-2010, 07:56 PM
zeke's Avatar
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Join Date: Sep 2007
Location: The Alamo City, TEXAS
Posts: 1,189
I had a similar problem....Changed the belt and voltage reg. with no effect. I found some rotten wires that terminated at the 3-pole connector on the firewall side behind the aux. cooling tank. These wires connect the alternator/starter CCU with the ignition switch somehow. I cut the rotted portion away from the each of these wires and spliced in new 10g wires and it fixed the problem..

YMMV, but it is something to look at.
__________________

Current Mercedes
1979 maple yellow 240D 4-speed


Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT
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  #3  
Old 09-27-2010, 08:18 PM
muleears's Avatar
Old MB Driver
 
Join Date: May 2006
Location: Windsor, VA
Posts: 1,435
Thanks Zeke. I have some CCU issues too, maybe the problems have a common cause. I'll check the wires. Don't have a pic by chance do you?
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Muleears
'07 E320 Bluetec 133K my DD
'04 Jaguar XJ8 VDP, 34K
'10 Hyundai Accent 60K Grocery Getter
'02 VW Golf soon to be on the road again
'97 E300 Diesel Son's DD
'61 VERY tolerant wife

Hampton Roads, VA USA

Gone but not forgotten:
'67 250S 95K
'86 300SDL
'87 300D Turbo, 364K! R.I.P.
'98 E300 Turbodiesel, 213K
'02 S420, 164K
'01 Prius 138K
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  #4  
Old 09-27-2010, 10:36 PM
cirrusman's Avatar
Just add Diesel.
 
Join Date: Aug 2008
Location: Salt Lake City, Utah
Posts: 587
It could be a number of things. I'd check the electrical contacts coming out of the alternator to see if there's current going to the battery. Check this with a tester light; you'd plug the positive end of the tester at the alternator and the negative at the battery's negative pole. If the light comes on, you have current. If not, there's your problem; alternator will have to be replaced.
If the battery charge bulb is burnt, the alternator won't charge, it's worth checking. If the current from the alternator to this bulb is interrupted somehow (Blue wire coming out of the alternator), same thing, I'd check it as well. Since you have a multimeter this should be easy for you. And if you have a tester light, even better, you can check if there's current getting to the instrument cluster. You will have to take out the cluster, but that's a breeze in these cars. On my '83 300SD the wires that bring current to this bulb are #7 and #9, and they're numbered in my cluster. Don't really know about yours, but it can be similar. One's blue, the other one's blue and white. If you have no continuity here, It can be a pain but you'll have to find the place where it's shorting and replace it. Although I doubt it's that since those wires don't see much sunlight or are in much contact with the elements, but it's worth checking if your alternator checks out good.
Good luck!
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[/SIGPIC]~cirrusman

1983 Mercedes Benz 300SD - Wife calls him "Chitty Chitty Bang Bang"
[SIGPIC]




1983 Toyota Tercel (Tommy, The little Toyota that could)
1965 Ford F100 (Grandma Ford)
2005 Toyota Sienna (Elsa, Wife's ride)


Gone:
1988 Toyota Pickup
2004 Subaru Outback

1987 Cadillac Fleetwood Brougham
1986 Volvo 740 GL Station Wagon - Piece of junk.
1981 Volvo 242 DL 2 Door - Hated to see it go. R.I.P.
1987 Pontiac Fiero GT
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  #5  
Old 09-28-2010, 02:15 PM
zeke's Avatar
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Join Date: Sep 2007
Location: The Alamo City, TEXAS
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Here ya go....great pics of the wires I replaced in this thread

revisiting alternator upgrades and rewiring
__________________

Current Mercedes
1979 maple yellow 240D 4-speed


Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT
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  #6  
Old 09-28-2010, 07:06 PM
muleears's Avatar
Old MB Driver
 
Join Date: May 2006
Location: Windsor, VA
Posts: 1,435
Right now the car is sitting in the drive, after a 15 mile drive. Idling with the fan on high and high beams on the voltage at the battery is 12.37. If I rev it up a bit, it will go to 12.9. Shouldn't I be getting over 13.4-13.5 volts? I'm letting it sit and idle to see if the alternator can keep up with the drain.

Zeke- I haven't had a chance to check any wiring and its getting dark.

I'll post an update in 20 min. or so.
__________________

Muleears
'07 E320 Bluetec 133K my DD
'04 Jaguar XJ8 VDP, 34K
'10 Hyundai Accent 60K Grocery Getter
'02 VW Golf soon to be on the road again
'97 E300 Diesel Son's DD
'61 VERY tolerant wife

Hampton Roads, VA USA

Gone but not forgotten:
'67 250S 95K
'86 300SDL
'87 300D Turbo, 364K! R.I.P.
'98 E300 Turbodiesel, 213K
'02 S420, 164K
'01 Prius 138K
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  #7  
Old 09-28-2010, 07:29 PM
muleears's Avatar
Old MB Driver
 
Join Date: May 2006
Location: Windsor, VA
Posts: 1,435
Quote:
Originally Posted by muleears View Post
Right now the car is sitting in the drive, after a 15 mile drive. Idling with the fan on high and high beams on the voltage at the battery is 12.37. If I rev it up a bit, it will go to 12.9. Shouldn't I be getting over 13.4-13.5 volts? I'm letting it sit and idle to see if the alternator can keep up with the drain.

Zeke- I haven't had a chance to check any wiring and its getting dark.

I'll post an update in 20 min. or so.

It's been 20 minutes, idling under full load and the battery still reads 12.4 volts. What does this mean? When it comes to electrical stuff I'm lost. Should I read the voltage with the car off and see what that says?

Thanks for the help.
__________________

Muleears
'07 E320 Bluetec 133K my DD
'04 Jaguar XJ8 VDP, 34K
'10 Hyundai Accent 60K Grocery Getter
'02 VW Golf soon to be on the road again
'97 E300 Diesel Son's DD
'61 VERY tolerant wife

Hampton Roads, VA USA

Gone but not forgotten:
'67 250S 95K
'86 300SDL
'87 300D Turbo, 364K! R.I.P.
'98 E300 Turbodiesel, 213K
'02 S420, 164K
'01 Prius 138K
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  #8  
Old 09-28-2010, 08:26 PM
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Quote:
Originally Posted by muleears View Post
It's been 20 minutes, idling under full load and the battery still reads 12.4 volts. What does this mean? When it comes to electrical stuff I'm lost. Should I read the voltage with the car off and see what that says?

Thanks for the help.
It means that you are not charging. A good fully charged Battery can have 12.50- 12.75 Volts. This is after the Battery has sat for 1 hour.

You can use your Volt Meter to test the Connector that plugs into the Alternator.
Pull the connector off. There is 2 wide slots that have Fat Red Wires going to them. Put your Red probe in one of the large slots of the Connector and the Black Probe to ground. You should have Battery Voltage there all of the time; even with the Key off.

There one small slot on the connector that has a skinny Blue Wire. This is the Wire that goes to your Charging Light.
Put the Red Probe in the small slot and the Black Probe to a ground. With the Key off you should get no voltage at all there.

Do the above but with the Key on but do not start the Engine. With the key on you should get slightly less than the Battery Voltage. If you get that voltage the Light Bulb in the Charging light is OK.
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  #9  
Old 09-28-2010, 09:16 PM
muleears's Avatar
Old MB Driver
 
Join Date: May 2006
Location: Windsor, VA
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Quote:
Originally Posted by Diesel911 View Post
It means that you are not charging. A good fully charged Battery can have 12.50- 12.75 Volts. This is after the Battery has sat for 1 hour.

You can use your Volt Meter to test the Connector that plugs into the Alternator.
Pull the connector off. There is 2 wide slots that have Fat Red Wires going to them. Put your Red probe in one of the large slots of the Connector and the Black Probe to ground. You should have Battery Voltage there all of the time; even with the Key off.

There one small slot on the connector that has a skinny Blue Wire. This is the Wire that goes to your Charging Light.
Put the Red Probe in the small slot and the Black Probe to a ground. With the Key off you should get no voltage at all there.

Do the above but with the Key on but do not start the Engine. With the key on you should get slightly less than the Battery Voltage. If you get that voltage the Light Bulb in the Charging light is OK.
The charging light comes on when I start the car but has not come on any other time.

Since I have already replaced the voltage reg. is it safe to say I need an alternator?
__________________

Muleears
'07 E320 Bluetec 133K my DD
'04 Jaguar XJ8 VDP, 34K
'10 Hyundai Accent 60K Grocery Getter
'02 VW Golf soon to be on the road again
'97 E300 Diesel Son's DD
'61 VERY tolerant wife

Hampton Roads, VA USA

Gone but not forgotten:
'67 250S 95K
'86 300SDL
'87 300D Turbo, 364K! R.I.P.
'98 E300 Turbodiesel, 213K
'02 S420, 164K
'01 Prius 138K
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  #10  
Old 09-28-2010, 11:27 PM
zeke's Avatar
Registered User
 
Join Date: Sep 2007
Location: The Alamo City, TEXAS
Posts: 1,189
If you feel the fuse terminals, are any hot to the touch?

your voltage is about what mine was doing...it should be over 13v

I was ready to get a new alternator, too but the wires did it for me...
__________________

Current Mercedes
1979 maple yellow 240D 4-speed


Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT
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  #11  
Old 09-29-2010, 12:07 AM
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Location: Long Beach,CA
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Quote:
Originally Posted by muleears View Post
The charging light comes on when I start the car but has not come on any other time.

Since I have already replaced the voltage reg. is it safe to say I need an alternator?
If the light comes on at all that means the Light Bulb is good. All of your warning lights are supposed to come on when you first turn the Key; that checks to see if all of the Light Bulbs are working.

Replacing the Voltage Regulator only increases the odds that it is the Alternator that is no good. It does not tell you if there is a wiring/circuit issue.

If you pull the Alternator out of the Car and have the Alternator by itself tested then you will know for sure. This is because I believe the Test Bench is going to have nice clean connectors a good Ground.

If the Alternator works on the Test Bench you have some other problem in the wiring circuit that goes to the Alternator and/or the Ground.
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  #12  
Old 09-29-2010, 09:44 AM
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Join Date: Sep 2006
Location: Middle TN
Posts: 4,154
I have had a voltage regulator bad out of the box. I had read about modifying the voltage reg by putting a diode in. I tried that & was over charging so went & bought another regulator. Now it charges fine.
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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.
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  #13  
Old 09-29-2010, 01:21 PM
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Join Date: Sep 2007
Location: The Alamo City, TEXAS
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I think this is good advice....will definitively tell you the condition of your alt...leads to either replacement and no more problems or some electrical wiring sleuthing.....

Quote:
Originally Posted by Diesel911 View Post
If the light comes on at all that means the Light Bulb is good. All of your warning lights are supposed to come on when you first turn the Key; that checks to see if all of the Light Bulbs are working.

Replacing the Voltage Regulator only increases the odds that it is the Alternator that is no good. It does not tell you if there is a wiring/circuit issue.

If you pull the Alternator out of the Car and have the Alternator by itself tested then you will know for sure. This is because I believe the Test Bench is going to have nice clean connectors a good Ground.

If the Alternator works on the Test Bench you have some other problem in the wiring circuit that goes to the Alternator and/or the Ground.
__________________

Current Mercedes
1979 maple yellow 240D 4-speed


Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT
Reply With Quote
  #14  
Old 09-29-2010, 01:48 PM
Craig
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Quote:
Originally Posted by zeke View Post
I think this is good advice....will definitively tell you the condition of your alt...leads to either replacement and no more problems or some electrical wiring sleuthing.....
I had a bad connection at the alternator plug that drove me nuts for months, I finally found it by wiggling the wires and watching the voltage at the battery change.

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