Trouble Starting-1977 300D - PeachParts Mercedes-Benz Forum

MrOwl42 · #1 01-04-2015, 02:16 PM

When I go to start it it sounds weak, like the battery is low and it's not going to start, but if I hold it for a little bit it will start, most of the time. I'm pretty sure it's not a problem with the battery because it should've died by now if it was but it's still starting. I looked up some diagnostic symptoms but nothing seems to quite match, headlights dim when I start go to start it, and it does eventually start up, it just takes longer than normal and sounds like it might not start. This happens whether the engine is hot or cold so I don't think it's just a problem with the cold weather. Any ideas?

leathermang · #2 01-04-2015, 02:24 PM

Where are you located ?
How long since you adjusted your valves ?
Have you tried charging your battery just before trying to start it ?
Have you made sure your wires to your battery....and the ground strap to the engine are all cleaned and not corroded ?
Are you sure all your glow plugs are working ?
Do you have the old style glow plugs or newer ones ?
Ever had your compression tested ?
How many miles do you think the car has on it?

MrOwl42 · #3 01-04-2015, 02:32 PM

Located in New York
I haven't, I've only relatively recently started fixing this car up, what valves/how do I adjust them?
Yes, still same thing
The wires all seem to be pretty good
The glow plugs seem to be working fine
Recently replaced them with the newer style
I haven't had the compression tested
Not sure on mileage, odometer doesn't work, it's stopped around 230,000

Assault · #4 01-04-2015, 02:58 PM

Go to an autoparts store and get the battery tested. I had a battery with 79% 800CCA and the car struggled to start. Not as bad as your scenario, but fairly close. Bought a new battery from Autozone with 950?CCA made a huge difference, as well as a new starter.

leathermang · #5 01-04-2015, 03:41 PM

That is good idea... take the battery.... that way you will be taking apart the connections to the battery and can clean them before putting battery back into the car... the dimming of the lights when you use the starter indicates an insufficiency somewhere in the system..
and about the starter... although they have HUGE brushes.... they DO finally wear out... or need the armature cleaned... or the three screws in the end which hold the ' basket ' the carbon brushes ... can get loose .. over decades... I take mine to a starter/alternator rebuild place in a farm town.. which deals with tractors and such rebuilding all the time...

MrOwl42 · #6 01-04-2015, 03:54 PM

Okay I'll check the battery. And interesting, the research I did said that the dimming of the lights was a good sign saying that the ignition switch was good, if I'm recalling correctly

leathermang · #7 01-04-2015, 04:03 PM

LOL

MrOwl42 · #8 01-04-2015, 04:14 PM

This is what I was going off of, not specifically for W123s though. Why Won't My Car Start?

leathermang · #9 01-04-2015, 05:09 PM

Your car is starting... so you know the key switch is working...

MrOwl42 · #10 01-04-2015, 05:47 PM

Yeah... I just listed the headlights dimming as something that might be relevant information... But I got the battery tested, they said it could use charging but in general was okay, so I'll try charging it, but I'm sorta doubtful that that'll work

leathermang · #11 01-04-2015, 06:24 PM

check the connections as I mentioned....
does no good to have it in the battery... but not get to the starter....
take off all the wire connections and clean with wire brush...
If no improvement.... take the starter off and have the auto parts store check it .....

unkl300d · #12 01-04-2015, 07:42 PM

replace the brushes on your alternator.

look it up in the archives.

if you have very cold weather, try cycling your glow plugs before cranking.

even if you have the newer style.

turn key until glow light goes off.

Remove key and repeat 2 more times, then crank.

see how it goes.

if you park indoors and its cold weather, try hooking up a trickle charger.

Coscto or harbor freight $10 cheapie.

see how it goes knowing the battery is topped always.

I had a similar problem last winter. battery good etc.

put a trickle charger on it during evening time.

once past the winter, no problems.

don't overlook your valve clearances in general. that can dog down engine start up.

vstech · #13 01-04-2015, 08:00 PM

Yes, the lights dimming as you crank IS a critical piece of information. It shows that the starter is pulling more amps than the battery can provide TO THE STARTER, or the starter is damaged, and pulling excessive amps.

Meaning, either the battery is discharged sufficiently to slow the starter crank speed, or the connections between the battery and the starter have degraded.
Have you changed the oil for winter blend, 5w40 synthetic? It will tremendously help with cold temp cranking. But, "looks good" is not the same as disconnected, and physically cleaned each connection.

I would start by battery brushing the battery terminals, and the cables. Take the ground cable off the fender, and clean the wire, the bolt, and the fender of all corrosion, and oil.
Then take the positive cable off the starter, and clean the wire, the starter, and the nut.

Also, under the car below the brake pedal area, there is a braided copper cable. Take it off the car, and clean each end, and the areas that it bolts to.
Reassemble, and report back.

sleepstar · #14 01-04-2015, 09:39 PM

have you had a valve adjustment done at proper intervals?
i had the exact same issue as you do. i had multiple places tell me my battery was "good, just needs charging". they'd say it was at 80%. putting in a new good battery fixed the problem.

MrOwl42 · #15 01-05-2015, 02:06 PM

Okay, sounds like I've got a lot to do, it might take me a little bit since I'm busy with otherstuff as well but I'll do the suggestions and tell you what happens