Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 10-18-2004, 10:41 AM
Registered User
 
Join Date: Apr 2000
Posts: 459
Strange charging/electrical problem

I have a problem that I can't quite figure out, so hopefully someone here can shed some light: when I spend a Saturday or Sunday running errands and making lots of short trips, eventually my battery runs down a lot. I know this because 1) the engine is cranking over noticeably slower, and 2) I can measure battery charge with a multimeter and it will read 12.24 volts, which is really low. I thought maybe I have a charging problem, but at idle I have around 13.85 volts, and around 13.95 at fast idle. I think that should be enough to keep the battery charged, shouldn't it? Because the alternator was charging properly I suspected the battery, and replaced it. Unfotunately, I had the same problem this past weekend, even to the point where the battery had barely enough juice to crank the engine. Can anyone suggest what the problem might be?

Here is the other piece of this puzzle. I know my starter is having problems because sometimes I will turn the key and nothing will happen. If I tap the side of the starter solenoid it will start. I guess this is a sign that the solenoid is going bad. But here is my ultimate question - is the fact that the starter is going bad the cause of my battery problems? I'm thinking that because the starter is going bad, its drawing more current than it normally would, and therefore lots of stopping and restarting the engine is running down the battery.

I would appreciate any advice. Maybe someone has had a similar problem. BTW, all battery cables and connections are clean.

Thanks,

GregS
'84 300D

Reply With Quote
  #2  
Old 10-18-2004, 11:07 AM
TonyFromWestOz's Avatar
"The Wizard of Oz"
 
Join Date: Jan 2004
Location: Perth, Western Australia
Posts: 834
1. At first glance it seems that your alternator is working, but it can deliver those voltages even if it can't put out the full current from the alternator. Can you get an Ammeter to put in series with the alternator output? Measure the current at ~2500 rpm and it should come up to the alternator's rated output, then reduce as the battery voltage rises (being recharged). You may have one or more diodes in the alternator open circuit.
2. Yes, a crook starter can drag heaps of extra current for little difference in cranking RPM. With your short runs and frequent starts, you may be dragging the battery down too much.

Check the alternator first, if OK, pull the starter and have it checked out and reconditioned if necessary.
__________________
Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.
Reply With Quote
  #3  
Old 10-18-2004, 04:13 PM
Registered User
 
Join Date: Apr 2000
Posts: 459
Can you suggest how I might check the amp output? I just called advance auto and Sears, and they both said all they can do is tell me whether its producing the right volts. Actually, Sears said all their diagnostic test can tell me is whether the alternator is "good or needs to be replaced." Whatever that means! A clamp on ammmeter would work, but I hate to spend $80+ for one of those just for this test. I already have a good multimeter, but it isn't the clamp-on type.

Thanks,

GregS
Reply With Quote
  #4  
Old 10-18-2004, 04:33 PM
boneheaddoctor's Avatar
Senior Benz fanatic
 
Join Date: May 2004
Location: Hells half acre (Great Falls, Virginia)
Posts: 16,007
Quote:
Originally Posted by GregS
I have a problem that I can't quite figure out, so hopefully someone here can shed some light: when I spend a Saturday or Sunday running errands and making lots of short trips, eventually my battery runs down a lot. I know this because 1) the engine is cranking over noticeably slower, and 2) I can measure battery charge with a multimeter and it will read 12.24 volts, which is really low. I thought maybe I have a charging problem, but at idle I have around 13.85 volts, and around 13.95 at fast idle. I think that should be enough to keep the battery charged, shouldn't it? Because the alternator was charging properly I suspected the battery, and replaced it. Unfotunately, I had the same problem this past weekend, even to the point where the battery had barely enough juice to crank the engine. Can anyone suggest what the problem might be?

Here is the other piece of this puzzle. I know my starter is having problems because sometimes I will turn the key and nothing will happen. If I tap the side of the starter solenoid it will start. I guess this is a sign that the solenoid is going bad. But here is my ultimate question - is the fact that the starter is going bad the cause of my battery problems? I'm thinking that because the starter is going bad, its drawing more current than it normally would, and therefore lots of stopping and restarting the engine is running down the battery.

I would appreciate any advice. Maybe someone has had a similar problem. BTW, all battery cables and connections are clean.

Thanks,

GregS
'84 300D
I had a regulator that sometimes overcharged (17.9 volts measured at battery post once, thats when I ordered a new one when I got home) smoked the Tach, half the dash lights and stereo, sometimes never charged and on 4 occaisions drained the battery overnight for no reason whatsoever. This was over the course of 8 months.

About the starter, check your connections first.
__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche
Reply With Quote
  #5  
Old 10-18-2004, 05:01 PM
Registered User
 
Join Date: Dec 2002
Location: RI shore
Posts: 2,937
years and years ago I got a DC ammeter fro JC Whitney that has 2 notches on the back, one large and one small. Lay it up against a conductor and the needle reads in amps. Not thoroughly accurate I'm sure, but great for a quick check. I'm sure it was a lot less than $10
__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.
Reply With Quote
  #6  
Old 10-18-2004, 05:03 PM
phidauex's Avatar
BioDiesel Hopeful
 
Join Date: Oct 2004
Location: St. Louis, MO
Posts: 806
"A clamp on ammmeter would work, but I hate to spend $80+ for one of those just for this test. I already have a good multimeter, but it isn't the clamp-on type."

Try one of these from Harbor Freight: http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=42396

Its harbor freight, so its not the best of the best, but I use mine all the time and it works quite well. Here is my rule for tools.. I buy a cheap one first, and if I wear it out, I buy a high quality expensive one to replace it. If I don't wear it out, that means I don't use it enough to justify the expensive one in the first place!

If you want to use a regular multimeter for current measurement, just disconnect one of the alternator lines and use the leads of the multimeter (connected to the amp reading plugs on the meter) to reconnect the line. IE, the current will go through the meter. Just make sure you have good alligator clips, and be careful.

Peace,
sam
Reply With Quote
  #7  
Old 10-18-2004, 06:22 PM
Old Deis
Guest
 
Posts: n/a
You can more or less get a good idea of the amp output by first measuring the voltage across the battery, which it looks as if you already have that, then turn on the headlights, heater fan, rear defrost, radio, every accessory you can and check the voltage again. It will drop, but should stay above 13 volts. If is drops below that you have a charging problem.
Reply With Quote
  #8  
Old 10-18-2004, 08:05 PM
Registered User
 
Join Date: Jun 2004
Location: West of Ft. Worth. TX
Posts: 4,186
Check your grounding straps both from battery to chassis and chassis to engine. I have ran across this problem in the past of slow starter spin up and charging problems. Much easier to do than pulling a starter also.
__________________
Sam

84 300SD 350K+ miles ( Blue Belle )
Reply With Quote
  #9  
Old 10-18-2004, 09:01 PM
Waitn For The Bus All Day
 
Join Date: Jul 2004
Location: south east pa.
Posts: 1,786
I had a bad diode in my alternator that caused the same sounding symptoms, but the starter could also be "dragging"-cranking slow due to worn brushes.

BTW, I did the same-replaced my battery first. Oh well, I got a new battery out of the deal so what the heck.

Cheers,

Bill
Reply With Quote
  #10  
Old 10-18-2004, 09:05 PM
Registered User
 
Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Look in the Yellow Pages for an alternator/generator/starter repair shop. They will usually be able to test the charging system in the car, along with starter draw.

If the starter draws too much current, you need a completely rebuilt on with a new armature -- just cleaning, turning the commutator, and new brushes won't work since the real problem is excessive resistance in the armature. That is what causes both the high current draw and the slow cranking.

Most likely you have a couple diodes out in the alternator, so that you can only get 20A or so out of it, and repeated starts with a "tired" starter will drain the battery.

If you get a dim glow on the alternator lamp at night, the brushes are worn out and you need to replace the voltage regulator (or have the above mentioned repair shop put new ones on, only a couple bucks!).

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
Reply With Quote
  #11  
Old 10-18-2004, 09:23 PM
whunter's Avatar
Moderator
 
Join Date: Dec 2003
Location: Metro Detroit, Michigan
Posts: 17,359
Thumbs up Good advice to follow.

Quote:
Originally Posted by psfred
Look in the Yellow Pages for an alternator/generator/starter repair shop. They will usually be able to test the charging system in the car, along with starter draw.

If the starter draws too much current, you need a completely rebuilt on with a new armature -- just cleaning, turning the commutator, and new brushes won't work since the real problem is excessive resistance in the armature. That is what causes both the high current draw and the slow cranking.

Most likely you have a couple diodes out in the alternator, so that you can only get 20A or so out of it, and repeated starts with a "tired" starter will drain the battery.

If you get a dim glow on the alternator lamp at night, the brushes are worn out and you need to replace the voltage regulator (or have the above mentioned repair shop put new ones on, only a couple bucks!).

Peter
By your description the solenoid is bad now, and will stop working shortly.
Unless you like walking or paying tow trucks, it needs to be fixed ASAP.
__________________
ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1980 240D
1983 300D
1984 190D
Reply With Quote
  #12  
Old 10-19-2004, 01:58 AM
romansek
 
Join Date: Jun 2003
Location: Dallas, Tx
Posts: 190
Do not invest in the clamp-on ampmeter

The clamp-on ampmeter will not mesure DC current. It is only for AC current. I recommend procedure discribed by "Old Deis". Your starting problem will not cause to discharge of the battery. If the starter is not turning than is not using the battery unless has short (observe dimming of the dome light or voltage on the battery).

Roman
------------
87 300SDL 157K
86 300SDL 212K
86 420SEL 226K
81 300D 147K
Reply With Quote
  #13  
Old 10-20-2004, 09:49 AM
Registered User
 
Join Date: Apr 2000
Posts: 459
I tested my car last night according to "Old deis'" suggested method, and here is what I got:

1) first test with engine idling and no accessories on - 14.01v;

2) turn on radio, headlights, and heater fan - drops to 13.95v;

3) turn on high beams, defroster, and a/c - drops to 13.65 (engine still at idle, and volts increase a little when the idle is increased (to about 13.68v or 13.7v));

4) turn off all accessories and test again at idle - back up to 13.9v and 13.95v, goes to 14v when I rev up the engine.

O.K. This does not sound like a bad alternator does it? There is serious amp draw when all these accessores are on, and with such good voltage readings I just don't feel comfortable accusing the alternator. Could I still have an amp output problem with such good voltage readings? On the other hand, I still don't know why my battery would be weak at times (reading as low as 12.24v when the engine was off), or whey my starter won't always engage. Is the starter not engaging because the battery is low (from a charging problem), or is the battery being drawn low because of a worn starter?

GregS
Reply With Quote
  #14  
Old 10-20-2004, 10:20 AM
Old Deis
Guest
 
Posts: n/a
Those test results do eliminate the alternator as being the problem. You are showing good voltages under load. I would not be concerned about the 12.2 v with engine off. That is a good reading as well.
Sounds like a starter to me. Could still be the cables, but the starter is looking like a suspect from here.
Reply With Quote
  #15  
Old 10-20-2004, 11:36 AM
Registered User
 
Join Date: Apr 2000
Posts: 459
Thank you. And I agree, looks like I'll replace the starter.

Greg

Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not 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 On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 10:18 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page