About a month ago my battery light came on dimly while driving. I kept using the vehicle as normal and noticed that the battery was not charging as well. Finally last night I had to get a jumpstart. After checking and replacing the voltage regulator I got a jumpstart. The car started and ran for about 5 seconds then died. I repeated this several times and each time the same thing. I had my buddy watch the voltmeter at the battery terminals. 12 volts at the battery, jumpstart, voltmeter shows 6 volts at the battery terminals, then the engine dies and voltage jumps back up to 12.

Assuming the alternator is bad will that really cause the engines to stall? The fuel pump is OE/mechanical so I never imagined this issue could exist. Is there anything else to check?


I also added a ground strap to the engine but it does not seem to have any effect with this issue.

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The battery can actually be disconnected once our OM617's are running.

The car may be stalling because the battery voltage is too low (at 12 volts) to heat the glow plugs adequately and/or spin the motor fast enough when cranking.
So.. yes, indirectly a bad alternator can cause stalling by affecting the battery charge.
You really need about 12.75 or more volts to start an OM617.
When the engine is running, a good alternator will be charging the battery at 13 or more volts.

Cold weather is hard on batteries, how old is the current battery?

Try cleaning the battery terminals and the cable connections and hooking the battery up to a charger overnight.

It should start right up if the battery accepts a full charge.

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I'd just get the alternator and battery tested and go from there. I'd suspect something causing the alternator to put too much load on the engine, causing it to die. Could be it's trying to keep up with a bad battery, could be it's bad itself. But you'll never know unless you start testing things. Once it's started it should stay started, though.

A quick test would be to take the belt(s) off, start it, and see if it stays running then. But that wouldn't tell you much beyond what I said above and you'll still need to do the tests.

-Rog

Thank you guys for your inputs!

Let me run just one more thing past you guys:

Once I got the car started I tried hitting the throttle, just to make sure the load wasn't too much at idle. Initially the car revved up, but without releasing the throttle after a couple seconds the engine would start decreasing RPM until it died out again. Does this sound like a symptom of anything else I can check?(I can see that there is fuel in the pre-filter so I'm sure it's getting fuel)


Thank you guys again! I'll post an update after getting battery and alternator tested

It could certainly be a lot of other things, but you have to start ruling the obvious things out. Removing the alternator belts would tell you if there's anything else to investigate.

-Rog

Fuel shutoff may be failing or getting vacuum, or the pcv hose may be blocked...

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Oh my gosh PCV valve. I pulled the stock air box out since switching to a cone filter. I switched a while back after leaking exhaust burned through the turbo intake elbow, but just today pulled the actual filter housing out and reconnected all of the PCV piping directly to the oil return. I figured it would return at least some oil and it's not airtight, but I'm sure there is backpressure in the system

The alternator might be seizing up.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

why is your negative battery connection going to the air cleaner mount, remove it. its not helping you. Also you need new air cleaner mounts.

So let's get this straight...

Battery Voltage = 12V

You jump-start the engine and Battery Voltage = 6V

Engine Dies and Battery Voltage = 12V again.

Correct? If so, you have an alternator or battery issue. Probably bad diodes or a battery hooked up in the wrong polarity. There is no reason why the voltage should go DOWN when the engine is running.

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Well the PCV was the culprit after all. I vented the PCV to atmosphere and now it runs. I had no idea that could be an issue

Nothing wrong with extra earth points if you can get them in place .I will do this with my w124 .But i maybe put it in another location ..

Strange since the intake is wide-open (no throttle plate) in an OM617 (assuming, always state year and engine), so the intake should always be close to atmospheric. There is no PCV that I know of, just an elbow and tube that vents blow-by gases into the intake. If the blow-by has a lot of engine oil, that wouldn't stop it from running, indeed it just burns that oil and can even idle on that oil, i.e. making the engine hard to stop.

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They had the crankcase breather tube hooked back into the sump, blocking it. The engine was shutting off because the crankcase pressure built enough to push the back side of the vacuum shutoff actuator (something unique to MB diesels)

OP should still check the weird voltage thing though IMO...

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It's a 1984 300D 617. Sorry I should have stated that.


The voltage is fine, IDK at what point it hit 6 volts but the buddy that gave me a jump isn't a car guy, he was just conveniently available at the moment.

I had no idea there was a vacuum shutoff actuator in the crankcase