There have customer who have Mercedes w176 (a gasoline with 270 engine year 2013) and it is a pain in the ass. The car came with a platform because it would not start. He run a quick test using the SD connect C4 mux and all control units were clear. He tried to start the car but the engine would half turn and stop. Something was cutting it off electrically.
Furthermore, without any obvious reason, the engine fan started working and the communication with the engine was lost. He have discovered that the the engine control was loosing a ground point. that is why the engine fan started. He have put an outside earth and the car came back in engine turning and cutting out electrically. He tried everything.
checked all fuses and relays (including the mini relays)
replaced terminal 30g relay
replaced exhaust camshaft sensor
checked crank sensor with oscilloscope and looks ok
tried second key
guided test for drive authorization (all ok)
and many many more
But still no fault codes.
So how to do next ? Suggestion from the experienced :
The problem with most technically inclined individuals trying to fix a dead engine is that we tend to quickly forget ”THE BASICS” ingredients for combustion to take place just so the engine may run!
1. Check for spark, is it there throughout or intermittently or not there at all,
-Famous L5, ECU, DI coils, e.t.c
2. Check for fuel rail pressure ( challenging on any A-class but doable if u want it to start and run),
furthermore M270 has piezo direct injection. so u have to find a way to confirm that fuel is delivered (repair fuel system accordingly)
3. Check for compression and make reference to specific values in WIS.
( Notice : this is a discussion in the MH community; just post it here for sharing info only !)
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