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Discussion Starter #1
The way that it's supposed to start is that you turn the key until the lights come on and then you pull the glow plug button out halfway. You then wait for the salt-shaker looking round thing on top of the steering column to start glowing and then you pull it out all the way and it activates the starter motor.

When I do it to mine, the glow thing never lights up. When I pull it all the way out to start the car, the ignition lights dim a little, but that's all - nothing else happens.

I know that the engine runs and I know that the car transport company had it running. But it won't for me.
I've recharged and checked the battery and checked the connections but to no avail.

It has to be something simple, but I can't work out what
 

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I have this car - I suspect that you are not waiting long enough. Remember the "salt shaker" is not very bright and that the the longer you have the starter switch pulled out the brighter it gets (and hotter the glow plugs get) but on a mild day you might not need to heat them that much. On a cold winters day you will need to heat them much more. This is different from the 1976+ years where they have a bright light bulb that goes off when you can start it.

Also you didn't mention it but you do should turn up the idle (the small thumb screw next to the ignition key) before you try to start cold and leave it up for one or two minutes on a mild day, longer on a cold day. It will stall if you don't. If it does not stall or the idle adjust seems to make no difference then either the idle is adjusted too high or the cable is broken.

On this car the glow plugs were wired in series with the slat shaker stock (often called "loop type" glow plugs because the plug had a loop). There are kits to "upgrade" them to "pencil type" which are wired in series; if you do this you may or may not wire the salt shaker in the circuit. Perhaps someone has done this to you car but if it is stock the salt shaker will light as you warm the glow plugs.

How can you tell if you car has been "upgraded" - look at the drivers side of the engine you will see the fuel injectors and next to them the ends of the glow plugs -- if they are connected in series by large uninsulated wire that looks a bit like a seat spring (a couple of S shapes) this is stock. If they are connected by individual wires they have been messed with.

I have the original configuration and see no reason to mess with it. But glow plugs do go bad and if that happened in the original configuration - depending how it went bad (open or short) if could leave the car unable to start. In the 47 years and 440,000+ miles I've had this car it happened once. I actually did get it started by shorting the bad glow plug and drove to a mechanic. Finally no matter which kind of glow plug you have they do need to be cleaned - or rather the pre chamber needs to be cleaned out. Look on youtube for information on that.
 

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Discussion Starter #4
I have this car - I suspect that you are not waiting long enough. Remember the "salt shaker" is not very bright and that the the longer you have the starter switch pulled out the brighter it gets (and hotter the glow plugs get) but on a mild day you might not need to heat them that much. On a cold winters day you will need to heat them much more. This is different from the 1976+ years where they have a bright light bulb that goes off when you can start it.

Also you didn't mention it but you do should turn up the idle (the small thumb screw next to the ignition key) before you try to start cold and leave it up for one or two minutes on a mild day, longer on a cold day. It will stall if you don't. If it does not stall or the idle adjust seems to make no difference then either the idle is adjusted too high or the cable is broken.

On this car the glow plugs were wired in series with the slat shaker stock (often called "loop type" glow plugs because the plug had a loop). There are kits to "upgrade" them to "pencil type" which are wired in series; if you do this you may or may not wire the salt shaker in the circuit. Perhaps someone has done this to you car but if it is stock the salt shaker will light as you warm the glow plugs.

How can you tell if you car has been "upgraded" - look at the drivers side of the engine you will see the fuel injectors and next to them the ends of the glow plugs -- if they are connected in series by large uninsulated wire that looks a bit like a seat spring (a couple of S shapes) this is stock. If they are connected by individual wires they have been messed with.

I have the original configuration and see no reason to mess with it. But glow plugs do go bad and if that happened in the original configuration - depending how it went bad (open or short) if could leave the car unable to start. In the 47 years and 440,000+ miles I've had this car it happened once. I actually did get it started by shorting the bad glow plug and drove to a mechanic. Finally no matter which kind of glow plug you have they do need to be cleaned - or rather the pre chamber needs to be cleaned out. Look on youtube for information on that.
Thanks for the info. Yes, mine are definately stock - they have the bedsprings between them. And I've tried glowing it for a full minute at night and still no light from the salt shaker. But nonetheless the car does start, although not very well. But we're in late summer here so that probably helps.

What voltage are the glow plugs? I was thinking of shorting them directly off the battery to see what that does. reason I ask is that not all glow plugs are 12V - I've had some that were 6V. But I've stuck a multimeter on them during the glow phase, with no joy, so I'm not sure what's happening.

I do know the car is nonstandard, as it has the OM616 motor in it, not the original OM615.

But I'm going to rebuild it anyway, so I guess I'll sort it out then.
 

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OK for your amusement - at night (or other dark environment) open the hood (or "bonnet") such that you can see the "bed springs" while you try to start it. They will glow like the salt shaker should.

As you describe it I think that you have some bad glow plugs. They are most likely shorted to the engine block by the carbon buildup (common problem). This is in the MB service book - that you need to remove the glow plugs and clean out the pre chamber periodically (see youtube, several good videos on how to) but then check each plug to see it's working. If you still have Stock the voltage across ALL of them is 12v (so 3v each) but easy to check that while your are heating the plugs that each one is getting 3v. If (let's say) #2 is shorted to the block by massive carbon buildup then 3 & 4 won't get any electrons and won't heat at all. Explains rough start - especially if after engine is warm it runs well.

You might not have to rebuild the engine, just clean pre chamber and perhaps replace bed glow plugs. It's worth checking before you do anything to serious.

Good luck, and post photos of all the crud that comes out of your pre chamber and then how well it starts :)
Frank
 

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Discussion Starter #6
OK for your amusement - at night (or other dark environment) open the hood (or "bonnet") such that you can see the "bed springs" while you try to start it. They will glow like the salt shaker should.

As you describe it I think that you have some bad glow plugs. They are most likely shorted to the engine block by the carbon buildup (common problem). This is in the MB service book - that you need to remove the glow plugs and clean out the pre chamber periodically (see youtube, several good videos on how to) but then check each plug to see it's working. If you still have Stock the voltage across ALL of them is 12v (so 3v each) but easy to check that while your are heating the plugs that each one is getting 3v. If (let's say) #2 is shorted to the block by massive carbon buildup then 3 & 4 won't get any electrons and won't heat at all. Explains rough start - especially if after engine is warm it runs well.

You might not have to rebuild the engine, just clean pre chamber and perhaps replace bed glow plugs. It's worth checking before you do anything to serious.

Good luck, and post photos of all the crud that comes out of your pre chamber and then how well it starts :)
Frank
Thanks for the info. The rebuild isn't anything to do with the glow plugs - it's just the fact that it is badly worn and has terrible blow by. It also leaks oil when it is cold - never had a car do that before. And I'm respraying it as well - it'll be a full restoration
 
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