M104.980 - Cranks, not starting

[brette013]

So a family member drove the 300ce-24 recently to the shops and back, the car now refuses to start up. Cranks hard but not igniting. Drove it to work and back the night before and worked perfectly fine. The car had sometimes when cold, start up on the second go after stuttering on the first.

Am I right to think it could possibly be the distributor, crankshaft position sensor, EZL (Ignition Control Module), or a fuel related problem? The RACQ guy said to me it has no spark, so I'll lead with that.

[MMWA]

is the tach moving when the engine is cranked ?

if you don't have access to a scope, you can in a pinch use a multimeter with duty cycle reading on the round diagnostic socket.

If the TD (tach) output from the ezl is functional while cranking you can rule out the crank position sensor and then...
If the switched negative leg of the coil is never being switched to ground and is permanently +12 feeding straight through the coil while cranking the ezl is toast.

Note that they fail in other ways too, such as excessive current draw and no operation at all, but the above fault is the symptom 99.9% of the time.

its very easy to test everything even the crank position sensor with a scope in a matter of seconds but not everyone has one at hand.

Personally if the EZL replacement is necessary, i would be replacing the coil, leads, cap, rotor, insulation disk and plugs with new oem / equivalent to prevent future failure, those EZL's dont come cheap for the 24 valvers.

[brette013]

I am hoping its not that EZL but cannot rule it out as the car has done 230000km's, unknown on ignition parts, and its failure to start was almost instantanous.

With testing the system out so far, started first at the crank sensor and found that the RPM needle moves when cranking. Put a multimeter on its sensor wire to the EZL and its resistance says something between 850-950. I think that's within spec so its probably good.

Don't know how to test EZL so I've left that for now. Resistance for the primary side of ignition coil is between 0.2-3 (I believe spec should be 0.3-0.6). Secondary resistance is reading 8.93 kw (sorry don't know how to read multi's very well, tested on 20k setting), but if I'm understanding it right is ok at it should be between 8-13. Thinking about replacing the coil and seeing what happens as the primary reading puts me off.

Haven't tested distributor yet as I need to get a torx bit to remove it to get access.

Using this as reference, think its for 123-126 models but figure ignition system is largely the same ke-jetronic - http://www.mercedes-club-bg.com/Mercede ... ic/EZL.pdf

[brette013]

Also looking up EZL part no for my car, it says the new part no 016-545-04-32 replaces the old 012-545-21-32 that i'm running. If anyone knows, should I believe that this would in fact work if I do resort to buying new version? Randomly searched it here https://www.genuinemercedesparts.com/oe ... NCZyPTU%3D

[Ivanerrol]

Before running out and buying another EZL. Check the crank position sensor - with a multi meter.
Also the coils die.
There's a MAS relay box - replaces the old Fuel pump relay and AC relay. Another suspect. (do the fuel pumps whirr when the ignition key is turned before cranking the engine?)

[brette013]

Fuel pump buzz's after turning ignition on. Already looked at crank sensor with multimeter, looked alright to me.

[brette013]

Just wanted to end this by saying it was my ignition unit module. Pretty costly those EZL's are, the old one in the car was a Siemens but now it's a Bosch unit.

Had changed the ignition coil but it didn't fix anything. As a positive the new Bosch version compared to the old Bosch does looks shinier (e.g. no engine grime), but did notice its design is slightly different that the old one.