300 TDT won't turn over / new battery....
 

With no warning my car (87' W124 / 603) won't start - still stuck in the parking lot at work. The battery is about 6 months old. Turn the key - nothing. I got a jump with good battery and good cables- nothing. It doesn't even begin to turn over. My question: would the starter be the next most obvious culprit or is there something else peculiar to diesels or the 603 that I should suspect? Thanks for any and all advice.

The first thing you should do is check your battery cables and connections to see if they are lose or corroded. Another thing is that you ight want to check your battery anyways, I have had a few bad batteries. As for the starter, I wouldn't know if that could be the problem, but I am sure someone else would.

Thanks 123c - I forgot to mention that I still have power when I turn the ignition - lights, radio, dash lights etc..... just no power to the starter.

So can you hear anything when you turn the key, like any noise from the starter? Once when I experienced a bad battery, all the electrical stuff worked, I had someone try jump starting me, and after letting the glow plugs cycle through, the battery had enough juice for the lights and stuff, but would do nothing when i tried to start it. I got it started by taking the jumper cable and connecting it directly to the lug on the starter. When I did this, i disconnected the cables from the battery. Try this, and if your car still won't start, then it would most likely be the starter.

Bryan,

There are a couple of things that could be going wrong. To sort this out you need to check the battery voltage. With nothing on, no key in the starting switch, you should have 12.5 Volts or more. If not, the battery or the system has a fault. Assuming the battery is good, when you cycle the key to the glow plug position, you should see a drop in voltage. When the light goes out on the dash, the glow plugs stay energized (the light is just a timer to tell you the minimum time the glow plugs need to be energized), and you should see another drop in voltage as the solenoid is energized, then another as the starter is energized when you turn the key to start. If you only see one event, that may be ok as the solenoid is not likely to spend a significant time switching the starter motor from off to on. To follow this sequence you need a second person to move the key as you watch the meter.

Assuming the battery is ok, if the solenoid does not engage, you either have a bad starter switch, solenoid, or the safety switch is not working. I am unfamiliar with this safety switch feature as I have had little experience with automatic transmissions, but it seems there is a switch that prevents operating the starter in anything but Park and Neutral on the transmission. It seems the Park position gets crudded up or something and can stop working. To check this just try starting in Neutral. If it works in Neutral, you have to have the safety switch cleaned or replaced.

If the starter switch on the dashboard is defective, you can tell this by manually running a wire from the positive terminal on the battery to the solenoid connection on the starter. I am not familiar with the way this is set up on the W124 cars, so I cannot give you much in the way of detail here. The solenoid connection is typically a lighter duty wire than the starter motor wire, and solenoid wire does not come directly from the battery. On W123 Diesels this wire comes from a bus junction/connector on the passenger side (in the US anyway) inner front fender, which makes it very easy to perform this test. If jumping the dash key switch works, the dash key switch needs to have the electrical end replaced.

If the solenoid does not work (it should make a relatively loud "click" and then run the starter motor) when you bypass the dash key switch, it needs to be removed, cleaned or replaced. This typically means taking the starter out and taking it somewhere to have the solenoid (also called the "Bendix" by some) replaced. At this point I would consider reinstalling a rebuilt starter, as the solenoid is typically pretty robust, and if it is shot, chances are other parts of the starter are about shot too. If the solendoid gives a loud click and starter still does not turn over, the starter is probably shot but it could be the connections on the solenoid. Check to see if the battery voltage droops significantly when you turn the key to the start position. If so, the starter is probably shot. If that is the case, get a rebuilt one from FastLane. They are good quality rebuilds and reasonably priced.

Hope this helps, Jim

Thanks for the advice Jim, I'll try what you suggested - I'm sure you touched on the problem.