1979 300sd ignition problems
 

I have replaced the starter and a faulty neutral safety switch in a 116 chassis 300sd. The car started about 8 times or so then it began to do what it was doing before the n. safety switch was replaced: The dome lights dim when you try to turn it over but the starter will not turn. help!

Sounds like it might be a bad battery or corroded battery terminals. Try cleaning terminals and battery posts and check the battery by putting a voltmeter across the posts (not terminals) and read the voltage when attempting to crank the engine with the starter. If the voltage drops to few volts, the battery is bad. If battery seems OK, try the voltmeter across the terminals attached to the wires and try the cranking test again. If the voltage drops now, there is corrosion between the posts and the terminals.


P E H

BTW I forgot to add: you do not have ignition problems, you have starter circuit problems. This circuit consists of the starter motor, battery, solonoid, wires and various switches. One of more of these is what is preventing the starter motor from cranking the engine.

As far as turning the engine over, I never do it because the oil leaks out. LOL.

P E H

What If the problem is in the ignition switch? Would it not be an ignition problem?

Have you checked to see that the alternator is charging? It's very simple to do. With engine running, a volt meter should show something like about 13.5 volts across the battery. If charging the battery gets it going again, you should check this.

Good luck,

Clunker,

A diesel does not have an ignition switch. Only a gasoline engine has an ignition (spark) system and thus an ignition switch. A Diesel has what I call a key switch which turns electrical components on and off and energizes the glow plug relay and starter solonoid which connects the starter to the battery. The key switch works in conjunction with a vacuum valve which is connecten to a diaphram in the injection pump to shut off the fuel to stop the engine.

The actual "ignition" of the fuel. whether gasoline or Diesel, is internal to the engine either in the combustion chamber or the pre-combustion chamber.

P E H

Sounds good to me! The battery terminals are clean and the alternator is fine. When I try to "jump" the car off using my 240D, it damn near stalls the 240D, as if something is instantly and constantly drawing power. Any more ideas on where to look?

Clunker

Please! Check the ground strap from Neg to body, If it is loose on the body, you will get intermittant starts. Also, check connections at starter, and yes your ignition switch could be bad. It is the main switch which energizes the starter solenoid. It could be the solenoid is hanging up also, or it has burned contacts.

Check ground first, then see if you are getting 12 volts at solenoid.

Also, if this huge starter is bad and drawing a lot of current, then you need a new starter.

Sounds like excessive current draw to me.

Check the connection between ground strap from starter to frame, and from negative battery cable to frame. Either connection can corrode, and cause severe current draw problems.

Also, check the engine for ease of rotation -- if you have a bad water pump, power steering pump, or dragging AC compressor, you won't have enough power from the battery to turn the engine over fast enough. Ditto for ruined crank bearings (shudder).

Do you hear the starter engage? That is, do you hear a loud CLICK at the starter when you turn the key?

And did you get a Bosch rebuild or new starter, or just a cheap rebuild from the "guys down the street"? When these starters go bad, it is usually because the windings have excessive resistance. cleaning it up, putting in new brushes, and turning the commutator, the usual gas engine starter rebuild, won't fix the problem. The starter still won't work.

Clunger,

What do you mean that the 240D is almost stalled out when you jump the 300SD? Was there a big spark when the battery cables were connected? This would tell me that there was a big short somewhere in the 300SD. Or did the 240D almost stall out when the 300SD starter was energized? If the overload doesn't happen until the starter is energized, it sounds like a short in the starter. If a large current is being drawn from the batteries, it is NOT a problem with corroded terminals or bad connections. You are drawing too much current, not to little.

Do the headlights dim when the starter is energized? How about when both batteries are connected? If lights dim a lot, this is another indication that too much current is going thru the starter and is probably a bad starter even if it is a rebuilt starter.

P E H

i'm curious, how does the 240d almost stall when it's power is taken away? i've seen gasoline cars do this, but i thought a diesel could run on without an alternator or even a battery once it's started??? I'm not questioning anyone, just curious.
Ryan:confused:

The alternator is putting out a lot of electrical energy when the other car is jumped and puts an increased load on the engine that is driving it. Alternators don't run for free. You have to put in a rotational mechanical energy slightly higher than the electrical energy you get out. Remember the law of physics that says energy can not be created or destroyed, just converted from one form to another.

P E H

P E H

If you have the kind of current draw it sounds like you're getting something is also probably getting really hot too. After you try to start it a few times give a quick feel to the starter or solenoid to see if they are really hot (just watch out you don't burn yourself.) That will be a good clue on where to start.

To: RG5384
I guess what P.E. Haiges said is why. Its as if your cutting the engine off by the "stop" lever on top of the engine. It idles way down to the point that it can barely run.

The 240D idles down once the battery cables are applied to the 300SD with the ignition in the 300SD off. I will check the headlights when I engage the starter to see if they dim.