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ML320CDI engine cranks but does not start

M-Class (W164) 2006-2011: ML280CDI, ML320CDI, ML420CDI, ML350, ML500, ML550

ML320CDI engine cranks but does not start

Old 02-09-2019, 07:44 PM
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W210 (E230), W126 (300SDL)
ML320CDI engine cranks but does not start


I have an ML320 CDI (non bluetec) with an OM642 engine that does not want to start. It cranks, and after a few seconds times out and cranking stops.

History so far:
The car "ran out of fuel" due a really bad repair some knuckle head "performed", and the fuel line from the tank output into the rigid tube got disconnected. The driver at that time tried for quite a while to start the car, until giving up and calling to a tow.
After temporary repairing the fuel leak (rigid line is on the way) the engine started only three more times, enough to move the car to a storage location (my garage). It took quite a while to start it the first time, but after jumping the battery with another car, it started "easily". Next start was done after leaving the engine running for 30min to heat up (assuming bad glows), and it was really hard to start, but once it started we drove it into the garage.
One week later I tried to start it, and only by jumping it and lots of tries it ran, and only once, and since then I have not been able to start it, be it jumped, after leaving battery with a charger, etc.

I have changed both air filters, they were full of debris, and fuel filter. The tank does have fuel, scanner reported 47L, but just assumed it might be a bad reading (a few months ago the car had an issue were it was not reading fuel tank level), and added ~10L more, and scanner now reports 55L, so seems to be that there is fuel.

When trying to start the engine, DAS reports battery voltage goes under 11.x (DAS turns red); this does not happen if jumped.
I also checked waveform on camshaft sensor and it is working as expected.

One thing I noticed, is that when I try to start the engine, the DAS reports rail pressure at barely 120bar, most of the time 110~119bar, while saying minimum required is 120, interesting; and also quantity and pressure valves show a value between 30 and 50% each while cranking. Shouldn't pressure valve value either be at 100% or 0%, whatever it is for fully closed?, and quantity sort of "open" not sure this one.

I have not measured the leak from pressure valve, but the number I see on DAS while cranking makes me wonder if there is something else, like CDI computer opening it on purpose.

Also, no errors are reported at all. The vehicle has a couple errors, parktronic , rear SAM window heater, and top window issue, but nothing else.
If I try to start it with pressure valve connector disconnected, the CDI computer notices it, the same case with quantity value; the error is reported.

I am really out of ideas, if anyone can give me a help I will really appreciate it,

Ivan Kocher is offline  
Old 02-11-2019, 01:35 PM
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07 S550, 07 GL320, 03 SL500
At a high level it sounds to me like you are not getting enough fuel to the engine. It's just a guess but based on everything you are saying it seems to me that there is not enough fuel pressure

I can't remember if there is a port to add a fuel pressure gauge on the diesels? If not DAS can tell you what the fuel pressure is (and should be)

There are two pumps I believe.. one in the tank under the back seat, and one under the hood. One of them is a booster pump. If either fails you can have fuel pressure problems and car won't run.

I'd run all of the DAS fuel pressure tests, and follow any guided tests that it suggests after that. It seems weird to me that the CDI computer would do something funny right out of the blue. This sounds related to starving the engine of fuel..that is usually when fuel pumps burn out.
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Old 02-11-2019, 04:16 PM
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2008 ML320CDI 4Matic, 2006 C350
The fuel pump under the right rear seat is the Low Pressure unit. It is the one most likely to start failing.
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Old 02-11-2019, 11:23 PM
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W210 (E230), W126 (300SDL)
The car ran out of fuel once, empty tank. It was due to the fuel tank level sensors not working supposedly, that is what the owner said; and at that point it was taken to the repair shop that damaged the car for fixing.

I will ask for help to measure the low pressure pump side, as I do not own a fuel gauge, but know someone that has one
Will update as soon as I have info about it.
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Old 02-17-2019, 04:39 PM
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W210 (E230), W126 (300SDL)
Update so far on electric pump:
1. generates more than 7bar pressure after a couple seconds it is running.
2. flow is about 56mL/second. I measured 1.22L in 21.7 seconds

I measured these two number on the fuel filter output. Also it took like 18h for the pressure to go nearly zero after I powered off the pump, I wonder if this is normal.

In this page https://diag.net/msg/m42gozknibrjhlt701d3th52f5 the 642 fuel pump should at least have a flow of 500mL/9s, which is basically what I got. I cannot find in WIS what the right numbers should be. Also, the pressure gauge I used goes up to 100psi (~7bar), so I am not sure how much over 7bar it really produces.

Still engine does not start.
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