I was wanting to ask about the glow plug relay, that is supposed to click. On mine I cannot hear it if it does. It does light the light in the dash ok, and it stays on for the normal interval, I think. My concern is could it be not good if not hearing the clicks? Also, I was interested if it could possibly cause a no crank at times intermittently? I have been left stranded off and on numerous times, since acquiring the car. It out of the blue did it yesterday again, and I was left walking. It starts right up by jumping the car, and then it works again normal by the ignition switch. I know it could be the ignition switch, but if it was bad I wouldn't think it would automatically work normal again instantly always after jumping the car to start it?? Is there a schematic to verify the glow plug module is good or not? Any thoughts or help would be appreciated on this!

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Rebe

The no start issue is likely something else.

The relay would normally click after the timer trips to prevent the glow plugs from staying on too long.

It's easy to test. Put the car in the run/glow position on the ignition switch and then use a multimeter to test for 12v at one of the glow plugs. The 12v should go away after 30-45 seconds. If not then your timer is not working.

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I was just listening for it sitting in the driver's seat.

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Rebe

If you live in a City normal taffice noise might pervent you from Hear the Relay Click. If your Hood Pad is still that that would dampen the noise.

People have said if you turn the Interior Dome Light on whent he Glow Plugs Relay goes on the Dome Light will dim and stay dim until the Relay Timer shuts off.

If you ignore the Glow Plug Lignht and keep the Key in the Pre-glow Position you will get about 30 seconds of Pre-glowing till the Relay timer shuts off.

Since you do not have a Neutral Safety Switch a no Starter cranking issue can be caused by the Starter itself, the electical connections, the Ignition Switch or the Steering Colum Lock (because it turns the Ignition Switch).
Note that your Ignition Switch also turns on the Glow Plug Relay.

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84 300D, 82 Volvo 244Gl Diesel

Yes, it is a no crank when it happens. I have a new bosch starter on the car. I have ruled out the starter because, it will jump start ever time without fail from the starter, no issues there. The reason I had a question on the glow plug relay is that the wiring diverts there on the starter circuit. In the electrical diagrams it shows an electronic module, and the circuit enters in. My thinking was maybe something is not reseting in there from time to time. Once it did it at my garage, and I pulled the c46 I believe it was and replugged it. It then cranked right up. It like reset something? I am definitely not a master at deciphering the electrical schematics...so I just threw it out there as a check. If it is the ignition switch, it is a real bugger, I think, the way it works! I think, I need a trailing car every time I venture out with it!

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Rebe

That is because your Glow Plugs are on while the Starter is cranking on all of the Merceds that use the Pencil type Glow Plug.

The reason for having the Glow Plugs on during cranking is that the Glow Plugs heat the Air in the Precombustion Chamber to a higher heat the Engine Compression can.

Apparently Mercedes decided that it is better to put a properly sized Battery in and put up with the dural load of the Starter and the Glow Plugs being on during Cranking to gain the higher Heat of having the Glow Plugs on during cranking.

I don't know for sure but I doubt if the Glow Plug Relay Timer is on during Starter Cranking.

Concerning the module I have not read of that on the Forum before.
Try disconnecting the Moduel and have someone Crank the Starter while you have the Volt Meter connected to the Small Terminal at the Starter Motor or you could do the same with a Test light.
I am guessing that you are going to get Voltage there at least intermittantly. The reason is that in the Wiring diagram it shows a Violet/Purple Wire with a White Strip coming out of the Ignition Switch and going to Conecctor C146 that is located above and to the Right of the Accelerator Pedal beside the Upper part of the Councel (on mine to expose it you need to remove part if the Counsal panel don't now if that is the same on yours. I think the other different colored Wires go to the Backup Lights).
From that connector the Wire Changes to a Solid Violet/Purple Wire and goes to the Small Terminal on the Starter Solenoid.

Anoter test to do is to apply your Voltmeter to the Battery and have someone Crank the Engine and see how far the Battery Voltage falls.

It does not show this but I believe from there another Violet/Purple goes from the same small Terminal on the Starter Solenoid to the Glow Plug Relay.

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84 300D, 82 Volvo 244Gl Diesel

I would purchase one of the cheapo charging system monitors that plug into the lighter socket and see how your electrical system is behaving.

I had a nearly identical problem and it turned out that the glow relay was intermittently sticking on for several minutes after starting. When that happens, and particularly if you are doing multiple short trips with the car, it will quickly kill a battery. Even a brand new one.

The voltmeters are not as commonly available as they once were. I purchased mine from Amazon.

Other than that I suggest you try watching to see if the dome light flickers after ~30 seconds to indicate the glow relay has switched off. On my 1980 it is barely perceptible, but on my '85 it is quite evident.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

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Actually, the battery is not a culprit in the situation, because when the ignition switch is a no crank. I am just starting the car by using the battery in the car by-passing the ignition. The battery and the starter are always a positive in resolving the no crank issue.

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Rebe

Neutral start switch?

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83 SD

84 CD

Sounds like your ignition switch could be the culprit...

Have you looked at the wiring diagram for the car to see what else is in the starting circuit?

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Just took a peak, nothing else in your starter circuit other than the battery, ignition switch, and starter. If you've eliminated the starter and the battery, the only other component is the ignition switch.

You could wire a light bulb to the stater solenoid (where the ignition switch is supposed to provide the power to the solenoid, which engages the starter and thus the starter cranks over the engine). If when you turn the key, the light does not light, then you know the solenoid is not getting power.

Replace that switch sooner rather than later, because if it jambs so you cannot turn the ignition tumbler, you will be "up the creek". You'll need to be able to turn the tumbler to remove the tumbler and replace the ignition switch.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Well, I bit the bullet yesterday. I changed out the ignition switch on my '83 240D. I have been fighting an intermittent no crank, since my purchase last November. I bought into Mercedes Source info and tool to do it without the lock removal. It was supposed to be doable, but it was not for me. I decided to just remove the lock, and it was not a very hard job at all. If the tumbler is not locked up and free, it can be done after doing one very quickly no problem. I took my tumbler to a place and had it ultrasonic cleaned. I wanted to make sure it didn't have any tiny brass particules in it. On this car the FSM calls for the tumbler release wire to be .040 in diameter. That is pretty important on this one, and a large paper clip is exactly the right diameter for the job. Now, I will have to wait out the drive and trial to see, if it solved the no crank issue!

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Rebe

I had started the car a couple of times and shut it off shortly, after installing the new ignition switch. I decided to go for a short drive last evening with it. Bad news!! I got ready to start it after the glow plug light went out, and it was a no crank again. I am ready to call it quits on this. It wasn't the ignition witch after all!

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Rebe

I read through this thread as it has progressed, but don`t remember if it was said or done.

There is a ground cable between the engine and body on the drivers side. Look below the Oil Filter housing and you can see it. It is accesable from under the vehicle. Remove it and clean both contact areas. This ground can cause all kind of problems.

Charlie

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The no crank at times is finally put to rest. I found the trouble the following morning & got the repair made this morning. I didn't need the new ignition switch, but it springs back nicely. Also, it is nice to have a ignition lock system, that turns smoothly without any catches. It is nice to get beyond the inconvenience of being stranded at times. Thanks for the responses!

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Rebe