Hoping the collective forum wisdom knows the secret to solving this one, but it's got me stumped. Car is a 1998 E300 turbodiesel. Turning the key it will crank and crank until the battery wears down, but it doesn't fire at all, not even a sputter. It is getting fuel, I get fuel when I crack the injector lines, and also while cranking there is a fuel smelling smoke coming from the tail pipe.

The car has been driven daily. There was a known phantom drain on the battery, as parking it for 2 or 3 days would result in a weak/slow crank next time it was driven, but it always started. Just prior to this no-start condition, the car was parked for 2 weeks straight, and the battery went totally dead. I put it on a smart charger for a few days, and it has charged back up successfully now.... but no start.

I've attached an advanced code reader to the 38 pin plug, and there is only a single fault across all 18 modules in this car. The one fault is related to temp sensor in the transmission, and was present prior to this no start condition. There were also some "voltage too low" faults on a bunch of the modules, but after the battery was recharged, those have been cleared and have not come back.

And I had a spare Genuine MB K40 relay, so I tried swapping it, but no improvement.

Thanks in advance for any ideas!

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'98 E300 turbodiesel

Concerning the sitting 2 weeks straight it is possible that your Fuel Supply/Lift Pump Valves are worn and after sitting 2 weeks the Fuel that was supposed to stay in the Fuel Lines migrated back to the Fuel Tank. That could explain the cranking and cranking with no Stating. Buy the time you started to get fuel up to the Injectors the cranking speed was too low for the fuel to burn.

Some sort of fuel restriction could also cause the same symptom.

However, that does not seem consistent with getting Fuel to the Injectors nor the smell of fuel at the exhaust.

That leaves if your Glow Plugs are actually working or not. You can disconnect the actual wires that go to the Glow Plugs at the glow plug Relay disconnect the connector and test with an Ohm Meter. That checks if the Glow Plugs are open or not or if their resistance is off.

You can also leave everything connected and turn the key to the pre-glow position, listen for the click and see of the glow plugs are actually getting voltage. If it has a strip fuse on the glow plug relay you can look at it to see if it is burned or take an extremely close look at it to see if it is cracked (I had a cracked one and did not take a close enough look the first time I look).

You did not say if after charging the Battery the Engine was cranking at a normal speed.

Note there is going to be more then a few people that are going to vilify me for mention Starter Fluid.
A more radical way to see what is going on is to disconnect your Glow Plug Wire Connector from the relay so that your Glow Plugs will not go on and remove part of your intake duct so that you can safely spray in Starting Fluid. But, this is they way you have to do it. You have to have someone else start cranking the Engine while you spray only enough in to get the Engine Started. You don't spray till the Engine is cranking; that is the way to get the minimum amount in needed to start.

It is not safe to spray a bunch of starter fluid in and then run and turn the key on. When that happens you get a whole sudden mass of the stuff into your engine. In other words by yourself you cannot control the amount to keep it to a minimum.

If nothing at all happens with the starting fluid something is causing a lack of compression or improper timing in your Engine.

Tough choices.

I have seen Diesels Start on WD-40 sprayed into the Intake but the intake has to be rather short for it to work. But, the WD-40 is safer.
At one time they actually used to make starting fluid just for Diesels; but, I have not seen any for over 30 years.

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84 300D, 82 Volvo 244Gl Diesel

Yes GP's are all working, all tested from the plug 0.6 ohms and no GP related codes in the ECU. It's 80+ degrees here, so car should start fine even with all bad gp's.

Engine does feel like it's cranking normal speed. I took the battery charger off at 8 am this morning, let the battery rest all day, and then measured voltage at 6 pm this evening and found 12.72 volts. So battery seems ok i think.

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'98 E300 turbodiesel

There may be no fuel actually being injected into the Cylinders or something did in your compression (that can even be some sort of timing issue.)

Look in the small filter and see if there is black or greenish-gray-black stuff in it. If so your fuel system is plugged up

Do you have that vacuum shutoff I mentioned?

This sounds like one of those jobs where you are going to have to write a list of stuff to troubleshoot and methodically go down the list.

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84 300D, 82 Volvo 244Gl Diesel

If your Fuel Injection Pump has a Vacuum Shutoff on it try disconnecting the vacuum line from it and see if it stats OK like that. If it stats OK like that you may be having some issue with the Vacuum Shutoff on the Steering Colum Lock.

If you want to get fancier T in a vacuum gauge to the vacuum shut off line. While you are cranking the engine there should be no vacuum I that line.

The last one is even more bazar. If something is causing crankcase pressure or holding crankcase pressure (meaning not venting properly) the crankcase pressure can push your vacuum shutoff on the fuel injection pump (if you have one) into the shutoff position.

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84 300D, 82 Volvo 244Gl Diesel

Check all the fuses , especially those for ecu.
You mention it cranks and cranks , now is this because you hold key in position or flick and let go and it just keeps turning until you turn key off ?.

i did check all the fuses under the hood, including those on the K40 relay. I have not yet looked at those under the rear seat.

Engine cranks and cranks because I'm holding the key in the start position. Cranking stops as soon as I release the key. The odd thing is that it's not even sputtering or firing at all. Not even a little bit. I'm on day 3 now of cranking a bunch every morning and again every evening, with the car on the charger overnight.

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'98 E300 turbodiesel

Reason I asked is because in a normal start scenario you just turn the key and let go and the car will start itself , my Jeep with the Mercedes om642 engine does the same .... so if no signal from sensors (usually crank sensor)within a second or two then they stop cranking.
My Jeep had my swirl motor delete resistor short out on the inlet manifold and this blew a fuse (no 16) and the ASD (auto shut down relay )resulted in a no start and the engine would keep cranking by itself until I removed the key , I obviously had a warning light and four engine codes for inlet / turbo /boost etc as the blown fuse powers those circuits.
You having no codes I presumed that there was no ecu communication which would then lead to non stop cranking on a key flick start.

Ok, made a little progress today, but still a little confused.

In my attempts to start the engine, I thought the glow plug light was staying on longer than it typically should in warm weather. Usually when it's 80+ degrees, it's only on for a moment before going out. But it has been taking ~10 seconds to go out during this no-start ordeal. Maybe something malfunctioning in the GP system?

Next I tried unplugging the can-bus connector from the GP relay, and attempted to start. No change, it cranks and cranks, I get smoke from the tail pipe, but doesn't even attempt to fire.

Next I plugged the can-bus connector back into the GP relay, and unplugged the big 6-pin connector that runs to the 6 GP's. Attempted to start, and bam, fired up instantly and settled into a smooth idle. Woah!

Shut it off, plugged the 6 pin connector back into the GP relay, and attempted to start. Cranks and cranks but no-start.

Next I checked all 6 GP's from the 6 pin connector. All show 0.6 ohms, none are dead or shorted.

This is bizarre. I wonder if there's some odd malfunction inside the relay, causing some kind of "no start" signal to be asserted on the can-bus?? Anyone ever heard of this problem before on an E300? I sure haven't.

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'98 E300 turbodiesel