EMERGENCY, 300E will not start - PeachParts Mercedes-Benz Forum

Rahulio1989300E · #1 01-05-2008, 10:15 PM

Hello Everyone,

Okay, I have a weird problem on my hands.

This is what happened, on Friday morning about 5AM I begun my drive to Atlanta, from Dallas. I need my car for an internship I am going to be starting on Monday.

On the trip the car started and ran fine from home in Dallas. It was the first stop that the problem showed itself. The car would not restart at the gas station after filling it up. Checked the normal things, the battery was brand new and the connections were very tight. So we had to get it jumped. We decided to turn off all electronics and such in car to help the car. Drove a while, had to fill up again, same thing. Got it jumped.

Problem got a bit worse at this point, we had to haul ass out of the gas station on the 3rd stop since the engine would barely run in idle and would almost stall in drive or reverse. At speed, the car performed perfectly fine.

The final gas station we had before going into the city, same situation, no power to start the car. Here we thought that when we get to Atlanta, we cannot have the car stop on us. So we did something ridiculous and bought the battery from the person giving us a jump start.

So with a charged battery installed, the car was able to start itself. and we were off to Atlanta. Everything remained off until we had to turn on the lights. We made it back fine and the car never stalled while in the city.

I had a friend get a new 80amp alternator for me while I was en route. We installed it this afternoon and the car started up and ran fine. I took it for a 30 minute drive around campus. Car ran fine.

Then after about 3 hours. I went to move the car so my roommate could unpack his car. It would not start again. I popped open the hood and checked the wiring, all was good, until I got to the negative battery terminal. Loose!

I tightened it and it all started working again. I started and stopped the car about 6 times within 20 minutes to make sure it all worked. So far so good. I am going to let the car sit overnight to make sure it still runs okay in the morning.

Using a multimeter, I checked the voltage at the battery terminal at idle in P.
13.4 is what I got. Then I turned everything on, A/C, rear defroster, blower on high, headlights, driving lights, rear dome, radio, everything with a switch.
Got 13.1 to 13.3 at that point.

Any other things I should try to look at or check?

Are there any other things

G-Benz · #2 01-05-2008, 10:40 PM

The story indicated that our alternator was the real problem...seems as if you solved your starting issue once you replaced it.

Nominal charging voltage at engine idle is around 14.4 volts...your readings seem a bit low, although the 80-amp alternator is correct for your model.

Keep an eye one things to make sure the alternator you purchased doesn't have a faulty voltage regulator. I think your starting problems are solved, though.

Check the condition of your fuses while you're at it...I've had some fuses completely crumble in my hand when I pulled them for inspection...

Ferdman · #3 01-06-2008, 06:24 AM

Rahulio, I suspect the voltage regulator brushes on the original alternator were worn down so far that the battery was not recharging properly. A new voltage regulator would likely have solved the problem instead of replacing the entire alternator. If you still have the old altenator remove the voltage regulator and check the length of the brushes.

Rahulio1989300E · #4 01-06-2008, 12:40 PM

I had the voltage regulator replaced at about 185,000 miles for preventive measures. I did pull the old one from the 70AMP alternator and the brushes had about half an inch of length to them and still nice and springy. It was the KAE brand, and I kept it for my box of spare parts.

So I do not think the voltage regulator was the problem, or have you had a voltage regulator fail at about 15,000 miles before?