Slow Crank...searched threads but not quite same symptoms... - PeachParts Mercedes-Benz Forum

dmcginn2 · #1 07-03-2011, 10:46 PM

My 83 300SD has been cranking slowly...sometimes.

1. Checked battery voltage...12.43 volts.

2. Checked voltage when wife turned it over...battery voltage dropped to 6 volts...turned over slowly...but it did start.

3. Let it idle for awhile, turned it off and had to jump start it...starter turned over fine.

4. Checked voltage while idling...12.7 to 13 volts. Voltage dropped to 10 volts at idle when lights and fog lights were turned on.

5. Drove car for 12 miles, charged battery turned car off, and cranked right up no problems.

6. Took battery to auto-zone...tested fine. Weird since I would think dropping to 6 volts would be indicator of bad battery...

7. tested for some sort of drain on the battery with key off etc. Nothing.

8. cleaned connections at the junction box on the left side.

Haven't tried to restart yet. Figured I would let it sit a couple days and try starting it to see what happens.

I know starter motor only has 63k miles, Alternator is only a year and a half old/has approx 5k miles and battery is two years old.

Is this a voltage regulator issue? Or starter drawing too much power? Or any other suggestions?

kerry · #2 07-03-2011, 10:48 PM

Put an inductive ammeter on the starter cable and see how much amperage it is drawing.

vstech · #3 07-03-2011, 10:49 PM

either the battery is bad, or the terminal connections are glazed.
12.43 is only about 60% charged.
12.7 shows bad alternator.

dmcginn2 · #4 07-03-2011, 11:01 PM

I will try both ammeter and taking a wire brush to the cables.

One other thing I forgot to mention was the weekend before I had been messing with that junction on the passenger side because I discovered one of the wire's insulation was worn off...so I disconnected it wire taped it ups since I couldn't fit the heat shrink tube over the terminal.

It was the third from the left...red wire was on top, and two white wires below it connected to same metal connector.

That's when my problems started.

I also noticed that all the radio presets reset themselves once...so after the cranking issue I initially assumed a loose ground cable since I had disconnected it the previous weekend to work on that junction.

dude99 · #5 07-03-2011, 11:09 PM

sounds a lot like a bad alternator to me. Have you replaced the voltage regulator?

dmcginn2 · #6 07-03-2011, 11:25 PM

I was thinking alternator originally, but when I looked through the mnx records that I got with the car...receipts and all...a new alternator was put in Sep 09...and it only had about 262k on it then...and only 267k now. I have good records of mileage and mnx back to 1994.

Now the voltage regulator...not certain about that. I will have to find the alternator receipt to see if it was on there.

I want to believe it's the voltage regulator because it isn't expensive, and it sort of makes sense with the inconsistent voltage. I would think I would not see a drop down to 10 volts at idle (at battery posts...not cable connection) as normal by turning on the lights and fog lights.

The voltage changes when I rev the engine, but I figured that would be normal.

But sometimes at idle with nothing on, it is 12.7, sometimes it is slightly over 13. I would assume the voltage regulator would take care of that load and keep it constant?

Diesel911 · #7 07-04-2011, 01:26 AM

Quote:

Originally Posted by dmcginn2

I will try both ammeter and taking a wire brush to the cables.

One other thing I forgot to mention was the weekend before I had been messing with that junction on the passenger side because I discovered one of the wire's insulation was worn off...so I disconnected it wire taped it ups since I couldn't fit the heat shrink tube over the terminal.

It was the third from the left...red wire was on top, and two white wires below it connected to same metal connector.

That's when my problems started.

I also noticed that all the radio presets reset themselves once...so after the cranking issue I initially assumed a loose ground cable since I had disconnected it the previous weekend to work on that junction.

There is such a thing as Liquid Electrical Tape I saw sold a OSH Hardware. I am guessing they are not the only ones selling it.
I am guessing it is something akin to Dip Grip.

When I put an inductive Amp Meter on my Starter that is working normally it pulls about 150 amps.
The only local place I have seen selling the small inductive Amp Meters is NAPA. About 3 years ago they were selling for $23.

The below Pic I have listed as a Terminal Block for an SD; I do not know what year. Ignore the Clips as the original pic was showing how to hook up a Remote Starter Switch.
I am assuming that the Wires are all connected correctly to the Terminal Block.

dmcginn2 · #8 07-04-2011, 01:50 AM

That picture looks just like mine. The wires I tinkered with are the 3rd over from the left (right next to the right hand alligator clip in your picture).

I have an OSH right down the road here. Maybe I'll stop by tomorrow if open, and maybe to see if Harbor Freight has a ammeter.

150 amps...got it.

funola · #9 07-04-2011, 07:59 AM

To isolate wether it's the battery or charging system? put a charger on the battery till fully charged, then measure battery voltage while cranking. .It should not drop below 10 volts.

kerry · #10 07-04-2011, 09:19 AM

Harbor Freight has a clamp around ammeter for about $20 as part of a multimeter and I buy the liquid electrical tape the local hardware store.

barry123400 · #11 07-04-2011, 11:06 AM

The milage interval since the alternator was replaced might indicate a loose vee belt. If you can turn the small fan on the alternator by hand the belt is too loose.
When this occurs you only get partial charging from the alternator.

To add to the potential misery a lot of rebuilt alternators are questionable for durability.

funola · #12 07-04-2011, 02:34 PM

Quote:

Originally Posted by kerry

Harbor Freight has a clamp around ammeter for about $20 as part of a multimeter and I buy the liquid electrical tape the local hardware store.

I highly doubt the $20 HF clamp on ammeter (part of multimeter) will measure DC amps, AC amps yes but DC amps highly unlikely.

If you have one, please verify if it measures DC amps or not. If it does, please post the item number because I want one.

kerry · #13 07-04-2011, 02:42 PM

Quote:

Originally Posted by funola

I highly doubt the $20 HF clamp on ammeter (part of multimeter) will measure DC amps, AC amps yes but DC amps highly unlikely.

If you have one, please verify if it measures DC amps or not. If it does, please post the item number because I want one.

Good point. It doesn't according to the manual.

dmcginn2 · #14 07-04-2011, 03:54 PM

And the winner is vstech....

$2.99 battery terminal brush thing from harbor freight...did the job. Can't believe it was that simple.

Came home tested battery voltage, 12.4 volts.

Cleaned terminals and inside of cable connectors with the brush.

Started right up, and approx 13.5 volts at battery terminal at idle.

And I did get a cheap multi meter with clamp ammeter for $12.99 but it was only for AC. It's good for voltmeter in a jam...doesn't read decimals.

dmcginn2 · #15 07-04-2011, 06:49 PM

Ok maybe not. My wife and I made two short trips today, maybe about a mile, and on the second restart, it cranked slow again...

I noticed the a/c was on when I cranked it on the second restart.

Drove home and did some checking

Voltage at idle is barely battery level with the a/c on.

But the voltage doesn't seem to be stable at idle without anything on, it sits at 13 volts and then climbs a little almost to 13.5 volts. sometimes it sits at 13 volts even.

Definitley drops voltage at idle when you turn stuff on.

Turned car off, restarted fine.

I will try the voltage regulator next?