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#1
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Troubleshooting alt-battery no charge
I have now eaten over 5 batteries in the past 2 years in the 300TD. I cannot figure out what is going on.
First I replaced several batteries that would repeatedly discharge. The car would start fine for a while, then suddenly not start. Sometimes it would still glow, then not engage the starter, sometimes it wouldn't even glow. I found the wires that led to the 3 screw terminal block on the fender well right behind the rad. overflow tank were melted, so I cut them back enough to remove all the compromised insulation and wiring and spliced new ends on. Those ends seem to be fine - no more melting or excessive heat at the terminals, but the problem was not solved. Around the same time I also replaced the belts. After I got a new Interstate battery after replacing 3 wal-mart ones, we failed to start at a fast food place. I was able to tap on the starter and get it to go, so I thought maybe the starter was failing. So I replaced that. The problem still remained, so I replaced the alternator. The alternator that was in the car (reman Bosch) bench tested ok, but the bracket had loosened, and rubbed a burr into the lower bolt hole which made the body impossible to reinstall properly. I replaced it with a junkyard reman Bosch that also bench tested OK. When I put the jy alt in, the battery warning light would remain on until I gave some throttle, then it would go off. Initially, I was getting 13.7-13.9V at the battery depending on what I had on (lights, radio, AC, etc...). But over time this dropped. After a while, it was clear that the new alternator was also not charging. So I thought maybe I needed better output. So I ordered a 160A model. I still got the battery warning lights until I hit the throttle, and I was getting 14.1-13.7V at the battery. This weekend, we took a long road trip. After about 4 hours of operation, we stopped for fuel and had difficulty starting again. Soon the monovalve failed, then the AC compressor cut out. By the time we arrived at our destination, the window motors were very slow. We went to walmart and got another battery and that was fine for trips over the weekend. There were no warning lights on even at initial start-up. When we set out to return, we drove for about 3.5 hours and again the monovalve failed and the compressor cut out. We made a short stop (never killed the engine) and the lights were very very dim. The battery warning lights never came on. So we found an OReillys and bought ANOTHER battery (3 in the car by the end of the weekend!). It was getting dark, and I know that once we were going that was the only electircal we really needed to get home, so we headed home (4 more hours on the road) with only the lights on - I even turned down the cluster lights though those are led, so they are pretty low demand. I tested the voltage across the new battery with the car running and it was 12.29V We made it home with lights, but the battery was at 40% charge once we got home. Thus morning I tested the voltage across the alternator with the car running and it was about 1.2V. My plan is to get the new alternator bench tested to make sure it is still ok, then go to a junkyard this afternoon to get a new bracket to replace the L-bolt which is a little bent - though the belts seem to stay tight. I guess I might get a couple of replacement belts, though the ones on the car seem to be in pretty good shape and are less then 2 years old. Any other thoughts on why I can't seem to keep an alternator charging in this car? The other thing I have noticed is that I have my tach guage disconnected (the plug that goes into the amplifier rotted and I haven't replaced it yet. But it will occasioanally 'bounce' which I assume reflects a loss of ground. I know the cluster ground strap is connected well, so I am thinking this may be reflecting a discharge from a hot wire somewhere into the chassis?
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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 |
#2
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OK, just had the 'new' 120A alternator bench tested and it failed.
I think I will go buy a reman at a mcparts store so I can return it easily if the car eats another component. If the battery has been through a single discharge-recharge cycle, and is now holding 12.xV, and I install a new alternator, it should be safe, right? It is a battery that has been through multiple discharge-recharge cycles that is in danger of eating an alternator, right?
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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 |
#3
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Have you checked your grounding? Ensure the battery-chassis ground and especially the chassis-engine ground are clean and tight. If there is even slight corrosion around the terminals, it is best to remove and clean them and I usually add a little conductive grease for protection.
Another possibility not mentioned was the charge light (batt. symbol) in the cluster itself. If it doesn't light up when tested, then the field of the alternator won't enable charging. Another problem location I found was the regulator to alternator chassis grounding. Corrosion would cause the regulator to no longer charge. Again, cleaning and conductive grease has eliminated that problem. Corrosion, both on the "positive" and "negative" sides of the charging system will give you problems and the bad part is that they are usually intermittent problems which are a nuisance to troubleshoot.
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Sam 84 300SD 350K+ miles ( Blue Belle ) |
#4
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With all due respect, the problem is not the battery. Your charging system has a problem and as the previous post says, it could be our grounds.
The alternator bracket and adjusting bolt (that L shaped thing) must be in top shape. You should use only Continental belts as they are the best for this particular application and they should be clean and tight. Have you checked the voltage regulator on that alternator you pulled from the bone yard? There are two screws on the alternator that hold it on. Pull it off and see if the brushes are in good shape, longer than 1/4 inch and nice and smooth on the area than contacts the armature. If the voltage regulator is bad, your car will run on battery power and the battery will not be recharged when the engine is running. Lastly, you may have something discharging the battery at all times, even when you have it parked. You can narrow it down by putting your tester on the fuse block to see if any particular unit is drawing current. Just remove the fuses one at a time and test. Glow plug relays have been known to stick "on" causing constant discharge.
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"Life is tough...it's even tougher if you're stupid." John Wayne Dave Pawleys Island, SC '79 300CD Last edited by Daman858; 05-31-2011 at 03:12 PM. |
#5
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I have Continental belts. The bracket is is ok shape, (better shape than the one on my 240D which has had the same battery since 2007). The glow system seems to work as it should - I see a drop in voltage for maybe 5 sec (not sure, never timed it) then back up to 12V for the start.
The first thing I did before replacing the original alt. was replace the volt. regulator, then I moved that to the junkyard unit, so it had a new regulator, and the high amp replacement came with a new one, so it isn't that. The charge light had been working (like I said, it would come on, then stay on after start until I hit the throttle). Now, I am not sure. Will double check and also check fuses for excessive current with out engine running. I replaced the battery - ground cable last night, and tested voltage drop from hot terminal to chassis, and it was perfect. Will also check engine ground strap connection.
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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 |
#6
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I had a similar issue that turned out to be bad connections inside the plastic connector that attaches to the alternator. They were barely making contact and would stop charging when the wires moved around.
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#7
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I replaced the terminals when I installed the 120a alt
ground strap to engine is tight I couldn't get any current readings across the fuses I measured against the chassis...not sure if that's right? but the voltage drop across each fuse as I turn the ignition and turn on appliances seems in order I rechecked the 3 port terminal, and that seemed ok...I tightened up the screws a bit, but voltage was good from the ground point to both hot terminals.....really confused. Also, I should mention there was some corrosion I cleaned off of the #13 fuse (radiator side of the fuse), and some on the Ac compressor fuse on the cabin side of the block it self. I also found this older thread that describes my experience well. I do seem to get good charging for a little while when I installed both 'new' alternators, but them the voltage generated fell off as described by pdrayton: http://www.peachparts.com/shopforum/archive/index.php/t-180649.html The issue was never revisited after he tightened a starter bracket, but I don't think that is my problem. I did have a loose bracket on the original alternator due to a missing bushing on the L-bolt, but that has been fixed, and the alternator and starter both seem solidly mounted.
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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 Last edited by zeke; 05-31-2011 at 04:42 PM. Reason: add link to similar problem |
#8
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unplug the glow plug relay and remove it from the inner fender liner on the drivers side, just behind the headlight unit. There are 4 very small flat head screws that will come off and you can separate the unit in 2 parts. Mine was filled with water. Not good. It is a long shot, but it is 5 minutes that may show a problem.
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1984 300d 360,000mi(sold, I miss it!) 1984 300D 1973 450se 1995 E300 2006 E350 4matic 2016 E250 |
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