1977 240d turns over but won't start.
 

Ok, I am a novice with diesel and mercedes-benz vehicles. I recently bought my first MB, a 1977 240D (automatic), and decided that I enjoyed it enough that I wanted to keep it alive. From my point of view it ran well enough. I had no trouble from the vehicle until the weather turned cold. The winter last year was a bit more extreme than we are used to in my part of the country(western ky). For about a week it was horribly cold for the area, reaching 20ish below for a few days. i knew it was coming so i filled up the tank and put some diesel additive in to keep it from freezing up. After that, the car wouldn't start and apparently the block heater went out. It does turn over, but it doesn't start. So, I tried jumping it, replacing the fuel filters, and changing the glow plugs. After all that, I bled the fuel system. Then I decided to get a new battery, still nothing. With my meager knowledge, I have no clue how to fix this car. I am not sure if the block heater going out and it not igniting are linked. I checked the fuses, I looked at the relays, but I am not sure what a bad relay looks like. The starter is new as is the alternator. I am at the point that the car will be sold or fixed by a mechanic if I can find one that knows these cars. Any ideas or places to start would be very appreciated.

While changing the Filters was a good ideal you have 2 Fuel Systems to bleed the Air out of.
The Fuel Supply System runs from the Fuel Tank (Screen at the Bottom of the Fuel Tank), under the Hood to Plastic Primary Filter, to the Fuel Supply/Lift Pup up to the Secondeary/Fuel Filter, Into the Fuel Injection Pump Housing and out past the Fuel Pressure Relief/Over Flow Vlave and from there the Fuel ends up back in the Fuel Tanks.

(You will deal with less Air in the System by filling the Secondary Fuel Filter with Fuel when you install it.)

After that you need to start pumping on the Hand Primer till you hear a sort of buzzing or soft squeeling sound comeing from the Fuel Injection Pump. When you here that keep pumping some more just to be sure.
That clears the Air out of the Fuel Supply System.

If you cranked the Engine with Air in the Fuel Supply System that Air gets into the Fuel Injection System where it gets trapped in the Fuel Injection Hard Lines between the Fuel Injection Pump and the Injectors.
When Air is in there when you crank the Engine the Air Compresses but barely moves towards the Injectors and you can Kill a Battery and stress a Starter trying to bleed/get the Air out.
The soloution is to loosen the Fuel Injection hard Line Nuts at the Injectors and crank the Engine; allowing the Air an easy path to escape till you see Fuel coming out.
Tighten the Fuel Injection hard line nuts and attempt to start.

did you check the glow plug fuse? on early models it is somewhat hidden and it is separate from the fuse box that contains everything else. here is a tutorial:
Mercedes W123 Glow Plug Fuse and Fuse Box, Early Style Replacement - iFixit

The Glow Plug System used on you year and model can be problematic if you have the original Glow Plugs.
If there is a short circuit that burns somethng resulting in an open circuit; when one Plug burns all of them stop working because the electrical circuit is in series.

First check to see if the Fuse on the Fire Wall is burned. It sould be under a Plastic Cover.
If any of those Zig-Zag wires touch the Engine Block it will burn something. I think if the Wires are not in the Correct order something will burn.

I can only give you a basic trouble shooting. While the Glow Plugs are on start at the rear of the Engine and take a Volt Meter and ground the Black Probe somewhare on the Engine and apply the Ret Probe on the end of the Glow Plug and see if you get Voltage.

Do that to all of them. If one is not getting Voltage you know there is an open circuit.

Note that the original Filiment/Loop type Glow Plugs do not ground to the Cylinder Head like Spark Plugs do. They ground with that last Wire up front

You can do the above Test Light that does not have a Battery in it but the Volt Meter give you more infomation. Don't be disturbed if as you go down the line from rear to front on the Glow Plugs the Voltage decreases. It is supposed to work that way.

If you decide to replace the block Heater it would be a good idea to pull it out frist and check the size of the threaded end as a lot of Folks have gotten the wrong size that needs another adapter Bushing/Ring.
The problem is the Adapter Ring/Busing does not seem to be sold by itself.

Less effective but another option is a lower Radiator Hose Block Heater but ask the Forum Members which one is the best. I live in S. CA and know no dietails on them.

Adjusting the Valves properly helps with starting. As the Valves wear the Valve Clearance/Lash closes up. A lot of People think the Engine has Hydraulic Valve Lifters that don't need adjusting but that is not so.

If the back of your Fuel Injection Pump has a tube going to the Intake Manifold you have a Fuel Injection Pump with a Pneumatic Governor.

I don't know enough about them to comment on trouble shooting or if a Governor Diaphragm Leak or Housing leak can cause a non-starting issue.

These links are somwhat organized and it is easier to find stuff.

DIY Repair Links
DIY Links by Parts Category - PeachParts Mercedes ShopForum
PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles

Have you done a valve adjustment?

Is the primer pump leaking?

What type of glow plugs did you put in the car?

Have you checked the battery for voltage? You should be somewhere around 12.6 - 12.8V before cranking the engine.

I went through the same thing when I bought my latest one and it turned out the battery was putting about 12.4-12.5V -- just enough to make it sound like it should turn off, but not enough to fully turn over the engine.

Dkr.

The glow plugs are the "pencil" type, no loop. they had been changed over from the loop before i bought the car. I have not done a valve adjustment and the primer pump does not appear to be leaking. As for the glow plug fuse, it seem the previous owner may have bypassed it. I can see where it is supposed to be, but both wires are connected to one screw.

fuel
 

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... did you tried loosen the fuel Injection hard line nuts at the Injectors and crank to see if ANY fuel comes out?


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Without the block heater the average older example is not going to want to start below a temperature much higher than what you quote. Part of the reality of older indirect injection diesels.

You can upgrade the glow plugs to pencil plugs if you have the older series plugs. That will help but forget starting in really cold temperatures with out a block heater or an engine that is still a little warm.

Also synthetic oil helps lower the stating threshold as well substantially. Simply put though you need a block heater that works. I am surprised it got that cold as far south as you are in comparison to us in eastern Canada. .

There may indeed be some other issues that can be improved a little such as the valve adjustment already mentioned and making sure the fuel system is in good shape.

personally i think you need to verify the glow plug system is functioning. my friends 240D has the upgraded system and a loose wire prevented it from starting even in 60 degree weather.

i checked that the injectors were getting fuel, they are. i bled the fuel injection pump, it needed it. I Have checked the wires on the glow plugs, all snug. inside the glow plug light comes on and goes off after an interval. but, i am supposing that would not signal that the glow plugs are not working or would it? could it be a ground problem? but it doesn't seem to be firing. So a closer look at the glow plug system should be my next move i am guessing?

get a volt meter setup, measure from the block to the screw on each glow plug. if you have 10 or so volts to each plug, they are working. if you have zero volts to the screw on the GP, then your relay under the dash or a wiring problem exist.
if you are getting 12V, to each screw, most likely the plugs are all bad...

measure and report back what you have.

+1 on the valve adjustment... it's important for compression!