[rooshael]

I have a 1974 240D W115 on my hands that doesn't run. It has 81,533 original miles. It does turn over. I have a friend who is a heavy-duty diesel mechanic helping me out every now and then.

When we first came across it, the primer pump never got stiff from pumping and injectors weren't spraying when cracked so we figured that it was pumping air into the system. We replaced that with the primer pump mercedessource has for sale. It got slightly stiffer, but whenever it turned over there was still no fuel coming out of the injectors when cracked or all the way off.

We attached a temporary fuel system straight to the injection pump and from the return with a small 12v fuel pump. We pressurized it and that worked a small bit with a tiny spray coming from the injectors, but not the amount that would come out with that much pressure. All the air came out when we did this. Because there's some fuel coming from the injectors now, we ruled that the injection pump does not need rebuilding.

We tried spraying starting fluid while turning it over, which made it crank even slower than it was, and we started to figure that it was cranking too slow to start. We took all the belts off and the fan and the cranking remained the same speed, very slow.
The diesel mechanic I know is thinking that we need to replace the starter. Is this the way to go? Does anyone think we're missing anything?
Google Drive link to Mercedes 240D W115 Turning Over Audio

BTW: (Probably unneeded information, but kinda funny) The guy I bought it off of said he took two hours to replace the fuel filter, so we replaced it again in case he did something stupid trying to replace it. Not sure if he actually replaced something else and thought it was the fuel filter.

 

[rooshael]

To add, this is definitely NOT a battery problem. We used three different batteries on it to make sure. One from a working Excursion, a deep cycle rv/marine battery, and the battery it came with (2 weeks old when we got the car two months ago). We made sure to charge the one it came with and the deep cycle battery.

 

[rooshael]

Update:

Turns out starting fluid is awful for these mercedes diesels. Didn't do anything to ours because we only used a tiny bit and it sounded really bad for a few seconds, but if we had used more we may have had a problem on our hands..

We replaced the starter and it turned over much faster and sounded better too, but still no running. We ended up getting a used injection pump off a 76 240D that lost compression and was parted out. Starts fine and runs beautifully now.

The injection pumps for the W115/240D are interchangeable as long as it IS a W115 and has an OM616 4 CYLINDER DIESEL ENGINE.

It took about 4 hours to figure out how the hell to time the injection pump.

MERCEDES SOURCE SELLS A TIMING KIT FOR THE INJECTION PUMP. THIS IS UNNECESSARY TO BUY.

You don't need to have the special screw on dripper, you can just take the delivery valve out of the 1st injector, screw one of the injector lines (whichever has the best shape to drip into a can) onto it, and have it drip at 1 drip per second. You probably have to have a second or third set of eyes and hands to help.

It's very much caveman-german engineering if that makes any sense. The beginnings of unnecessary mechanical nonsense..

 

[300Dman]

What I don't recall reading is that you removed the Ground and battery cables and cleaned all of the areas where they connect. That is the most basic thing. I am wondering why a Heavy Diesel Mechanic would not have gone for that first.

My Symptoms were not the same but when I pulled off my Starter I found that the Brushes were worn out.

People have said that a like on my 84 300D turbo Diesel the Starters crank faster then a good stock 240D Starter. However, I cannot vouch for fitment issues I only have read that some 240D owners have done that.

 

[300Dman]

Note the starter swap might only work with 240D made in the 1980s.

When you use Starter Fluid you need to unplug the Glow Plug Relay or if you have the relay behind the Instrument cluster disconnect the Fuse on the Fire Wall. The Glow Plugs ignite the Starter Fluid before peak compression.

Thick crankcase oil in the cold also slows engine cranking when trying to start.

 

[300Dman]

See post number 6 in other site. I go by Diesel911 on that site. Checking the voltage drop will tell you if here is too much resistance in your Battery Cables.
As an example with one voltmeter probe on the positive Battery Terminal and the other on the other end of the Cable down at the starter when you crank if you cables are good you should see no voltage on meter because all of the voltage/current is going through the cable as it is supposed to.

While you are down there remove the Negative clamp on the Better and then remove the Starter cable from the Starter and make sure where it contacts is not corroded. And re-assemble and test.

Dying starter motor? W115 240 - PeachParts Mercedes-Benz Forum

 

[rooshael]

We didn't swap the starter. We bought a new one. We swapped an injection pump.