w123 electrical gremlins and other stuff, need help - PeachParts Mercedes-Benz Forum

dark hawk · #1 01-16-2016, 04:22 PM

About a week ago is was driving my 1984 300d home from work. It was -1 F if that matters. Anyways after about 4 miles of mixed driving my radio started to act up. After about another mile the battery light turned on but really dim and the radio went out completely. Finally I made it home turned off the car in my garage and attempted to start the car because I know that these cars can run without a functioning battery or alternator. The buzzer also sounded odd. I waited for the glowplugs to warm and cranked. It went crank pause, crank pause, crank and gave up. Tried again with the same result. I got out my jumper cables and attempted to jump it with my land cruiser. Same result strangely.

I swapped the battery out of the land cruiser into the 300d. It started like normal but all of the dash lights were on dim (brake, battery, ect). I drove it around the block and the temp and fuel gauges were going full crazy and were all over the place. Headlights did work they I cant remember if they were dim or not but either way it wasn't enough for me to notice.

I pulled a good relatively new battery from my parts car and installed it. I tested the battery and it was at around 12ish volts (I have a analog multimeter that can be kind of hard to read) I drove it about a mile before the gauges started to act up. Another thing is the gauges appear to read accurately when the car is in park sometimes. I have tested the battery with the car running a number of times since and though it is kind of difficult to read the multimeter I can tell its not close to 14v.

I went look at the voltage regulator but i was unable to because of a coolant hard line in the way of one of the screws. Also I plan to get a digital multimeter later tonight and test with that.

Any thoughts or ideas on what these issues could be?

BWhitmore · #2 01-16-2016, 04:27 PM

Sounds like a ground problem. Check to ensure that you have a good clean battery ground and also a good engine ground. The grounds for the instruments/radio, etc. are located behind the instrument cluster(brown wires) thus requiring pulling the instrument cluster out. The gauges will go wild because of a bad ground.

dark hawk · #3 01-16-2016, 05:19 PM

Any ideas on why I wasn't able to start it? It started fine when before I left work which is the reason I think it might not be ground.

BWhitmore · #4 01-16-2016, 08:03 PM

Does the engine crank but not start? If no crank try moving the shift lever to neutral. Could be bad shifter bushings which would throw off the neutral safety switch. A poor battery and/or engine ground will also cause a no crank.

pj67coll · #5 01-16-2016, 08:09 PM

My previous 240D had an ongoing battery drain charge light coming on etc problem. Was fixed by replacing the VR. Might be an easy way to try and fix it. If it works at least you won't be chasing other possibilities and if not you'll at least have a new VR and can eliminate that from the equation.

- Peter.

dark hawk · #6 01-16-2016, 08:39 PM

The no start issue was a while ago, it would barraly crank and would not start. Not an issue now though.

charmalu · #7 01-16-2016, 11:24 PM

There is a ground strap between the eng/tran adaptor plate and the body.
Remove it and clean both ends where it connects.
I had a problem, and this was the cause of it.

It is on the drivers side right about where the oil filter is.

Charlie

sleepstar · #8 01-17-2016, 12:14 AM

didnt believe the stories abotu the ground strap until it happened to a friend of mine. glow plug light would stay on, battery light would be on but dim, car wouldnt start. the ground strap had been sliced in half.

cfh · #9 01-17-2016, 01:50 AM

The radio going out is a classic symptom of the battery losing its charge - if you had been using your wipers you'd have lost them too. Could be a bad alternator but probably a bad ground - clean up the sheet metal and terminals for the battery negative to ground on the passenger side and the engine to frame ground down low on the drivers side. Also it can help to run a separate ground from the alternator to the body. The alternator grounds through its bracket connections and that can be affected by rust or corrosion or even paint.

dark hawk · #10 01-17-2016, 11:23 AM

Ok so I tested the battery with a proper digital multimeter. When it was off the new battery tested 12.2 ish v. When I turned the car on at idle it was in the lower 11v range. I then got in the car and revd it to 2k for a little a couple of times and testd the battery in the mid 13v range so that's good. I still haven't pulled the voltage regulator yet because its -8 and I really don't want to lol.

Thanks for the help, I'll try the suggestions.

Orv · #11 01-28-2016, 04:04 PM

You should be able to get 13.6-14.4V at idle, if there's no other electrical loads on. Sometimes the car has to be revved up once to get the alternator field going but after that you should get good charging voltage at idle. If you only get good voltage while the engine is held at higher revs, you probably have a bad diode in your alternator or some other problem. (Loose belt, glow plugs stuck on, etc.)

red55b · #12 01-28-2016, 09:38 PM

Mercedes diesels require alot of battery cranking amps to ignite diesel fuel you must be sure the new battery is in the correct MB battery group (a replacement of an old one is just not going to work long term) has proper cc/cca cold cranking amps there is a low # around 900 and high # up to 1200 also dont rely on volt reading or even battery under a load test (mc parts will say need new alternator) there is a battery tester that has clamps and checks conductivity of battery SOLAR tester
Get a Optima battery aka gel battery the fitment of Optima's is weird but worth it long term
Bosch batteries are great and perform better and longer than duralast and interstate Check out CTEK smart charger too its hands down the best recondition and all around battery charger w out over charging

patbob · #13 01-28-2016, 10:05 PM

Thought I'd read years ago on here about the glow plug relay sticking on and draining the battery faster than the alternator can charge it.

However, this does sounds like a bad ground, maybe at the alternator.

dark hawk · #14 01-29-2016, 09:34 AM

Yes I have considered that it was glow plugs staying on. Thing is that I can hear them clicking off so I have that ruled out. I drove the car this morning. Started up fine but with stupid dash lights. After about 3 mins of driving the radio started to act up again and eventually known of my electrically were working except for a couple of dash lights and my turns signals barely worked. I'm going to check out a couple of things later today and touch back here.

dark hawk · #15 02-03-2016, 09:59 AM

So I had the alternator tested and it was putting out at 30 maximum amps, factory is 55 or 60-65 I can't remember which. Anyways, 30 is 25 under 55 ehich based on what I have read an alternator should be replaced if it is putting out 16-20 under it should be replaced which it is.

However, Kent Bergsma says that these alternators are robust and rarely needs to be raplaced. I cleaned off the battery ground as well as the ground cables near it if you know what I mean so I don't think it is a ground issue but it is possible it is a faulty ground somewhere in the system.

I guess my question is do I appear to be missing anything? If not are alternator issues as rare as I am lead to belive? If so, should I get a rebuilt Bosch off of here or a used on off of eBay? Thanks.