AlexVx

Hello, I have no crank/no start problem with my clk350, 2007. Could you please advice on following?

Short version: authorization is fine, ECU works well on vehicle simulator, 1 error related to generator, no ground on starter relay, no spark and no fuel. I hear fuel pump noise on start.

Long version:
I bought it inoperable. Trying to fix for more then one month. Checked all available sources, did everything discussed in 'no crunk' topics, but still car don't crank and don't start.
Car was delivered to my house with dead battery (completely dead, 0 V), replaced with new one. Tested with obd scanner, there were two errors:

• B112E IC, the control unit is faulty(ROM: read error)
• 1337 Ecm, alternator serial interface (current and stored)

Display on instrument cluster was faulty, so I bought used instrument cluster and transferred memory to it (just found service on ebay and send them both instrument clusters). It fixed second error.
While cluster was in repair I took off the alternator and brought it to starter/alternator service. They told me that alternator on my car is like new and works well. I also checked voltage on starter relay and it seems like +12V is fine, but there is no ground. According to wiring diagram ground signal goes from ECU. So my next guess was ECU fault.
I found ECU repair service on ebay and sent my ECU to them. Vehicle simulator showed no errors.
So, currently everything seem to be fine with authorization: EZS (electronic ignition) and ESL (electronic steering lock) show YES everywhere, transmission module show OK when gear is in park, drive authorization in IC also fine. Used this video as a reference I checked wires from starter relay to ECU, from alternator to ECU, all fuses and relays in front SAM, to the left from steering wheel and in the trunk.
I tried to take out all the fuses, except engine related, to eliminate faulty module that cloaks CAN.
I found one story when no ground issue was fixed with a switch that added ground signal to starter relay, so I attached wire to the ground point and to the starter relay. Now the car cranks, but still no start. I checked the spark and fuel: took one spark out and placed it on the engine. No spark and no fuel - spark was dry, no sparks visible.
May be someone will have an idea what else to check? I don't believe that crank sensor is bad, because I can check engine speed with scanner while cranking (around 120 rpm). I hear fuel pump noise and scanner show that it's working. I still don't know why scanner show alternator error.

Rudeney

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120RPM is too slow. It may be a dragging starter or a bad CPS. Also, check pressure at the fuel rail - should be 50-60psi. Also, the starter gets ground form the block, so if that was the problem with it not working, you need to trace and repair your ground points.

AlexVx

Hi, thank you for your reply. Since it's a gasoline, not diesel, is it so important to have high rpm value? I guess it should be possible to start engine even with 120 rpm?
Thank you for suggestion with ground problem. My scanner show NO on 'terminal 81' in ECU, in GENERATOR category (I'm using professional Launch scanner, not Star). It's not an error, just Stream value. According to wiring diagram it could be a problem with Fuse F56. This fuse lives inside the wiring harness. Looks like it's a really rare problem. Found discussion about F56 here https://mbworld.org/forums/c32-amg-c...dden-fuse.html
I'll check resistance between the starter + and generator +. But still, it could be a root cause of generator error, but won't affect starter.

Rudeney

What's the voltage while cranking? If it drops below about 11v, you may have a weak battery (or alternator).

AlexVx

Good question! It depends on how to measure voltage. I can check it on battery directly with multimeter or with scanner from different blocks. Actually every block show different values. ECU 12.2, EZS 12.08, battery 12.6. While cranking voltage drops to 11 volts and then to 10.5. Battery is brand new, bought it from mb dealer and it's fully charged. Should it be 12.6 on all modules? (ezs, ecu, transmission)

Rudeney

You will see some voltage differences based on resistance. Th battery itself being at 12.6v is fine. I and surprised it's dropping down as low as 12.08v at the ignition switch.

AlexVx

Agree, looks pretty strange. Battery is very powerful (something like 100mAh). I checked resistance from the battery to alternator - it's close to 0, so it couldn't be wires.

AlexVx

So, after several attempts to start the car battery is completely dead, charged it to full. May be new battery require a couple of circles to get full power.
Noticed one strange thing: EZS: Turn enable issued = NO, ESL: Start enable = YES, ME motor electronics: Start enable =NO
I wonder what could cause Turn enable issued to be No? I hear Bzz sound when key is inside the ignition lock.

AlexVx

Finally fixed everything, easy:
1) replaced engine computer
2) replaced engine
Original no crank issue because of ECU synchronization, most likely battery died during the start