W123 no start/ start puzzle- beyond archives - PeachParts Mercedes-Benz Forum

unkl300d · #1 12-06-2013, 09:27 PM

Hello, I searched the archives for a hint of an answer but I still am inquiring.

This morning was quite cold for San Francisco. 47 degree F. 1979 300D.

After only cycling the glow plugs once, I turned the ignition on and the starter engaged normally and the engine turned for about 3 seconds, then it seemed like the starter disengaged without mechanical noises with what seemed like a disconnection of electricity as if due to a 'breaker' doing its job.

The 'breaker' is an analogy, I know there is no fuse or breaker on the starter itself.(aside from the strip fuse for the glow plugs)

tried again and same.

No weird noises other than the sensation of a quick disconnect of electrical power.

So later I moved the trans selector to neutral and allowed the glow plugs to cycle three times before starting.
Started normally.

Went for a short ride, parked. Restarted in Park with no problem. Temp outside was about 49 F.

I am curious to know what caused the symptoms.

Does the glow plug timer intervene when the glow plugs are not hot enough?
Although I did not hear the glow plug timer 'click' as the starter 'lost the power source'.
(normal sequence is to wait until glow plug light goes out and then turn ignition all the way)

I don't suspect the neutral safety switch or solenoid because the symptoms don't add up.

I have not tried cold starting it normally yet nor just in neutral.

In the meantime this query.

Here is a bullet list:

1) Did the engine turn over? -- yes for 3 seconds
2) Any clicking sound from the starter solenoid?-- NO, no starter grinding either.
3) Did you cycle thru the gear shift in all gears and end in park again? --later
4) Did you try to start in Neutral.-- later, coincidentally worked.
5) Did you check the battery terminals ?-- yes, new battery.

Thanks for your insights.