300D Charging Issue - PeachParts Mercedes-Benz Forum

InDiesel · #1 12-21-2008, 07:00 PM

Ok here is a rather weird one.

1984 300D Turbo Automatic. Started draining batteries about 8 months ago. I went through a couple of Walmart batteries, then figured out that my instrument panel problem (occasionaly erratic action in the tach, and fuel gages, etc.) may have been causing a charging problem since it is my understanding that the battery light is in the "charging" loop(?). I pulled the panel found a hairline crack in the PC board and soldered connections across the cracks. I also replaced the voltage regulator. Problem seemed to be solved.

About two months ago, another no start one morning. I deccided to get a "Die Hard" with over 800 CCA's. It seemd to work fine for a while. Did not perform a charging system check.

It worked for about a month, then I came out to start one morning, and no go. Battery was too weak. Jumped it off and went on my way. I ran around in the car most of the day with no problems. Then when returning home in the evening, with the lights on, heater fan blowing, and radio on, the lights started to dim. I turned everyting off except for the lights. Still they were getting weaker. As an aside, I have, on rare occasions, heard relays rapidly clicking behind the climate control area. I assumed that it was the climate control unit, but the lights would flicker somtimes when it did this. Figuring I didn't have much to lose since I was loosing juice to power the lights, I gave the console a couple of "Fred Sanford" slaps on the side. Rapid relay clicking started and the lights flickered. After a couple of more slaps, the lights retruned to "full bright" (brighter than ever it seemed!). I continued on home.

Next morning, battery was very, very low, (almost completely dead) and I jumped it again. I drove on a short trip and returned home. The car sat for several days with the windows partially open, so I had to cover with the "blue tarp".

Yesterday, I jumped the car(the battery was compelety dead) and went straight to Sears to get the system diagnosed. The battery was so dead it read nothing on their meter and wouldn't even charge becasue the charger didn't relize that the battery was connected. They popped in a new battery and tested. They said that it the system was reading "no charge".

From there I went to Pep Boy's to get the alternator replaced (and the voltage regulator). After replacement (the guy struggled with it for over 3 hours) the voltage was only about 12.5 volts at rev, 11.75 at idle. They said that there was really nothing more they could do and recommeded a "euro repair shop".

I brought home and tried to do some more diagnostics. I disconnected the Climate Control Unit and retested, but there was no real change. I also cleaned the ground cable at the body connection as well as the terminals on the terminal block. Still no change. I tried turning on all the power equipment to see if a big draw would kick the alternator in to "high gear", still no go. It also appears that there is some kind of drain on the system as well, but I do not have an amp meter to see how heavy the draw is.

This morning I went to Advance to get another Alternator so I could pull the voltage regulator off to see if replacing that would help. Still low voltage. So I returned the new one to it's proper owner.

Here is the deal, when I initially start, the voltage is over 13 volts at rev (12.7 or so at idle), but then drops back after about 3 or 4 seconds. It does this consistantly. I cannot seem to do anything to get the alternator (or voltage regulator) to kick in with some effective charging, or even above 11.7 volts after initial start. After I turn the ignition switch off, the voltage returns to about 12.25 volts. So I will resort to disconnecting the battery at night to avoid the drain.

Thus, I hereby call on the power of the Shop Forum for assistance. I have read through some of the charging issue posts, but nothing has helped yet. I am not ready to park this car yet, it has been my daily driver for about 5 years and everything works except the cruise control (and now the Climate Control, but that is for another thread).

I have assumed that the charging system is fairly simple and straight forward, but maybe it isn't. As always, any help is most appreciated.

Jeremy5848 · #2 12-21-2008, 08:25 PM

An interesting problem or problems. With the key OFF, all lights OFF, doors closed, etc. – so nothing except the clock and maybe a memory circuit in whatever radio you have is drawing power – and you disconnect the battery negative cable so the battery won't die overnight: is there a spark when you disconnect? Can you tap the negative cable on the battery post and make sparks as you connect and disconnect?

If you can make sparks, something more than the clock and the radio memory is drawing current. That is probably what is causing the battery to go down overnight.

If you do not get sparks, the battery should not discharge. If you have a VOM with an Amps scale, you can try measuring the current between the negative cable and the battery negative post. It should be only a few milliamps – just enough to run the clock, radio memory, etc.

Even if you do not get sparks, there could still be a problem with something loading down the electrical system when you are driving. One possibility is the glow plug relay. It can stick closed so that the glow plugs are on all of the time. Glow plugs draw a lot of current; the typical charging system cannot keep up in normal driving. You can do a very simple test by starting the car and then unplugging the 5-wire heavy cable that goes from the relay to the glow plugs. If the relay is stuck shut, your charging problem will go away when you unplug the cable.

Another test is to measure the voltage at any one glow plug. Once the engine has started there should be no voltage at the glow plugs. If there is still voltage at the glow plugs with the engine running, you have found a problem, if not the problem.

Jeremy

InDiesel · #3 12-21-2008, 08:57 PM

Jeremy,

Thanks for the tips. Will give it a try.

I do get a sparks when tapping the neg cable on the neg post. I believe that it is more than clock and radio mem.

I'l unplug the glow plug relay, test and report back.

InDiesel · #4 12-21-2008, 09:06 PM

Jeremy,

You were spot on with the GP relay issue.

Stuck GP Relay is the winner. Charging at 13.5 volts at idle with GP relay unplugged.

Battery reads at 12.5 volts now after ignition is off, so it added about .5 volts with just 2 or 3 mins of running even with lights and blower on for a little while.

Is the GP Relay field serviceable or is it a replacement part only (I haven't searched the forum yet, but thought I would ask since I am posting anyway).

Interestingly as well, no more sparking when tapping the lug to the post. I am not sure how this could be related, especially since I went ahead and reconnected the GP relay for tomorrow mornings start (it will be unusually cold here in Athens in the morning, I think in the 20's). I assume that even with a stuck relay, that the GP relay is not energized without the ignition being engaged.

I'll keep the post updated with my progress.

Thanks Jeremy. You are the quick diagnostic MAN!

InDiesel · #5 12-21-2008, 09:21 PM

Ouch $178.36 for a new GP Relay!

Someone please tell me I can open her up and "electro clean" it, file it, WD-40 it, or something.

79Mercy · #6 12-21-2008, 09:36 PM

I can grab a relay at the junkyard on Tuesday if you want me to. Send me a e-mail.

leathermang · #7 12-21-2008, 10:29 PM

Don't WD40 stuff like that... leaves residue...
go to computer store and find a spray solvent that leaves nothing behind...

InDiesel · #8 12-21-2008, 10:47 PM

Quote:

Originally Posted by leathermang

Don't WD40 stuff like that... leaves residue...
go to computer store and find a spray solvent that leaves nothing behind...

Thanks for the advice Leathermang.

The WD-40 part was rather "tongue in cheek". I was gonna add duct tape to the list as well, but forgot before I posted.

Good catch though, don't want someone casually reading and thinking it is a good idea.

Simpler=Better · #9 12-21-2008, 10:57 PM

Autozone has CRC plastic safe electrical cleaner for around $6/can