Electrical Peroblems with 300 SDL - PeachParts Mercedes-Benz Forum

julio.garcia.fc · #1 07-31-2011, 06:38 PM

Hello,

I am new to this thread. I hope this has not been asked before. If so, please point me to the correct thread. I could not find information.

My 300 SDL has been running great for a while. A few days ago, I stopped and turned off the engine waiting for a train. I was playing with the ignition switch to get the radio to come on, but not the glow plug. When the train went by, I could not start the car. The glow plug came on, but it did not have enough juice to turn the engine. I got a jump and went on my way. I thought that playing with the ignition switch may have drained the battery and after running for 15 minutes it would all be OK. Not so. The ABS light came on the ABS box in the engine compartment started clicking.

I changed the voltage regulator. The brushes on the old one seemed badly worn. No luck. The only symptom that seems to have changed since I changed the voltage regulator is that the ABS light is not coming on any more, and it is not clicking either, but that may be because the battery is so dead now. Now, I cannot even get the turning signals to work when it is running.

Other odd behavior include jumpy panel gauges. The speedometer jumps around a bit, the fuel gauge does not mark a full tank (3/4), even though it is (just filled it up), the RPM is at zero when the engine is idling.

A few days ago, this car used to start almost instantaneously.

When I jump it, it seems to run just fine, but most electrical things do not work or are sluggish. All this odd behavior started after that train stop. Any ideas?

I have owned the car for just a couple of months. It ran perfectly for the person who I bought it from. He is a close friend and I have know the car for 4 years. It is beautifully restored.

I hope you can help me.

NJ300sdl · #2 07-31-2011, 09:59 PM

Research OVP relay. It may the cause.

julio.garcia.fc · #3 07-31-2011, 10:17 PM

Thank you. I found this: OVP relay whys and wherefores

BTW, I hooked the jumper cables to one of my other cars and "charged" the 300 SDL for a few minutes. The battery took a charge and has held it. Not enough to turn the engine, but all the other "end user" electronics seem to be working. I am wondering if it is the alternator (???). I will dig some more into the OVP.

Jeremy5848 · #4 08-01-2011, 02:19 AM

Other than the regulator/brushes, the alternators are usually pretty reliable. You might try removing the regulator and looking at the slip rings (the things the brushes press against). If they are badly worn they might be able to cause your problem even with a new regulator.

Another possibility is a bad ground. Make sure the big wire braid strap is clean and well connected on both ends where it connects the engine to the chassis, somewhere underneath. Likewise, check the connection where the battery grounds to the chassis.

Jeremy

pimpernell · #5 08-01-2011, 09:08 AM

Quote:

Originally Posted by julio.garcia.fc

Hello,

I am new to this thread. I hope this has not been asked before. If so, please point me to the correct thread. I could not find information.

My 300 SDL has been running great for a while. A few days ago, I stopped and turned off the engine waiting for a train. I was playing with the ignition switch to get the radio to come on, but not the glow plug. When the train went by, I could not start the car. The glow plug came on, but it did not have enough juice to turn the engine. I got a jump and went on my way. I thought that playing with the ignition switch may have drained the battery and after running for 15 minutes it would all be OK. Not so. The ABS light came on the ABS box in the engine compartment started clicking.

I changed the voltage regulator. The brushes on the old one seemed badly worn. No luck. The only symptom that seems to have changed since I changed the voltage regulator is that the ABS light is not coming on any more, and it is not clicking either, but that may be because the battery is so dead now. Now, I cannot even get the turning signals to work when it is running.

Other odd behavior include jumpy panel gauges. The speedometer jumps around a bit, the fuel gauge does not mark a full tank (3/4), even though it is (just filled it up), the RPM is at zero when the engine is idling.

A few days ago, this car used to start almost instantaneously.

When I jump it, it seems to run just fine, but most electrical things do not work or are sluggish. All this odd behavior started after that train stop. Any ideas?

I have owned the car for just a couple of months. It ran perfectly for the person who I bought it from. He is a close friend and I have know the car for 4 years. It is beautifully restored.

I hope you can help me.

Most of the chain auto parts stores such as Autozone or Advanced Auto would be happy to check out the battery and alternator to see if they are up to snuff. When you jump the car and start it, if you remove the jumper cables, the engine does not require any electrical power to run. If your alternator is not putting out enough voltage, your electronics will not operate as designed. If you have a spare battery that is fully charged and place it in the car, and you still get the same results regarding the electronics, then you might have a more involved issue that just the alternator. Good luck!!

86-300sdl · #6 08-01-2011, 09:45 AM

I've found that these cars seem to go through batteries. Particuarly if the proper one is not installed. I get a new one every three to four years. Especially if I am spending a lot of time in 95 degree + areas. For me if even one cell is not up to speed it is time for a new good battery.

TX76513 · #7 08-01-2011, 11:01 AM

On your SDL there is a outboard connector on the side of the positive battery cable make sure that connection is clean and tight. I overlooked that and it cost me many hours of trouble.

julio.garcia.fc · #8 08-01-2011, 11:31 AM

The battery on it just now was purchased May 2008. Sounds like I may need a new one? I checked the voltage and it is 13 or a little less. I will take it to autozone a little later today.

I take it is OK to drive with no battery or with a bad alternator?

Thanks!

winmutt · #9 08-01-2011, 11:49 AM

Maybe your GP relay is stuck in on pos eating juice? I had this happen with my 87 recently.

sixto · #10 08-01-2011, 12:27 PM

Quote:

Originally Posted by julio.garcia.fc

I take it is OK to drive with no battery or with a bad alternator?

Okay for whom? Don't drive on the street without brake lights and turn signals.

Sixto
87 300D

julio.garcia.fc · #11 08-01-2011, 12:40 PM

Yes, of course. I put enough charge in the battery to get turn signals and break lights working for ~30 minutes or so before I go anywhere. I just want to make sure I do not fry anything else.

julio.garcia.fc · #12 08-01-2011, 04:43 PM

Well, I just had the battery fully charged and tested. It is good. They also tested the alternator and the diagnosis was a bad voltage regulator, which I just changed. It is a new one. I have not changed a regulator before, but other than carefully placing it in the same way as the old one, is there some special secret to doing it? I made sure the brushes were aligned and pressed up to align the screws.

I hope the image shows up OK, if I did it right. Note that while the image does not show both screws, both are in there now. I had to replace on of them. Whoever replaced the regulator before stripped the screw head.

julio.garcia.fc · #13 08-11-2011, 09:09 PM

FYI, it was the alternator.

yuke · #14 08-13-2011, 09:07 AM

Check your glow plug relay to see if it stuck in the on position had this happen on my 85 300SD took 9 months to figure it out.Right now you probably do not even need the glow plugs to get started so pull the connection on the relay and see it it ends your dead battery issue.I also hooked up a volt meter on my dash and can immediately tell when I am in a discharge state which has not happened since I replaced the relay.Oh I see you found the problem great job.

julio.garcia.fc · #15 08-15-2011, 04:21 PM

Where is the glow plug relay?