My 96 E300D has suddenly died. It starts, revs momentarily and then immediately shuts down. After a few seconds delay, trying to start it again will do the same thing... again and again. Continued cranking on the starter will cause the occasional cylinder to fire and make me feel optimistic, but it will never actually start. I have checked the 40 relay and the fuel cutoff valve, both seem good. The relay clicks and the COV opens momentarily when the key is turned to on. I had the dubious idea to manually turn on the cutoff valve with a couple of jumper wires to the battery. The engine started right up and went to full throttle (Very exciting). Hasty removal of the jumper wires immediately killed the engine. The cutoff valve was replaced about a year ago. There is no air in the fuel and I'm using an inline electric fuel pump that is providing 7 psi to the fuel system. I can see lots of fuel flowing through the lines and filters. All the filters have been replaced. It went from running very well to completely dead. Any ideas would be greatly appreciated.

Hard to kill once running; suggests a massive air leak (usually at 1 of 2 orings at prefilter) or a clogged tank screen maybe.

Follow the fuel path and look for bad seals especially 1-3.

fuelflow.JPG (image)

Check the routing of the fuel lines. People have reversed them before after working on them. Will idle but not accellarate usually.

Why are you using an electric pump? Veg setup? The lift pump works by creating suction and pulling fuel up through line 3, line 4 becomes pressurized and then goes back to the IP and finally to the inj's.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

Thanks for the suggestions, I added the electric fuel pump to eliminate the lift pump as a potential problem and to prime everything after I replaced the fuel lines and filters. (not necessarily permanent) No veggie here, burning nothing but dino fuel. No air at all in the fuel lines, the electric pump circulates quite a bit of fuel through the system. The problem occurred suddenly, before any work was undertaken, and nothing I have done (changed filters, changed all fuel lines, added pump) has made any difference. Suspect is the computer control of the cutoff valve, but not sure how to troubleshoot it.

Seems like you verified operation of the SOV with the jumper bit. I think the K40 relay controls the valve, I think it like $100 from the dealer, I would think about swapping it out.

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1996 E300 110,000
1985 300TD 212,000
1980 300D 238,000

You don't want to have to replace the computer that controls the IP -- it is at least $1000. As johninva writes, the K40 relay (in the black plastic box on the right side of the engine, where the battery isn't) is about $100 and is sort of an updated version of the over-voltage protection relay of earlier models. If it fails then the IP won't get any electricity. It is a common cause of engines suddenly going dead. You can replace it yourself, it just plugs in.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Great suggestions. I replaced the K40 relay board, but no change. Using a voltmeter, I can see power going to the cut off valve momentarily, but then it turns off and stays off. Are there any other sensors or fuses that may cause the computer to turn off the engine?

Hmm- the symptoms match what I read would happen with bad fuel lines or o rings sucking air (supposedly you would see bubbles in any clear lines tho), or a bad k40 relay... Maybe bad wire/connection or bad ground? Hope you're able to track it down- keep us updated.

Well, after spending a week at the local independent shop, we went through a series of diagnoses, he looked at the security ignition key, the K40 relay and the fuel lines. I found it gratifying that these were all the same things that were suggested in this forum. Great minds do think alike.

In the end it turned out to be the crankshaft position sensor. When it goes out, the computer shuts the engine down immediately after starting, but doesn't throw a code to the OBD port.

Thanks for all the help.

I know this is old, but was the replacement of the sensor something a novice can do?

Mo in NJ