Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Hello and welcome to Just AnswerIf the EGR valve is stuck open then this can effect starting so try disconnecting it to see if this helps or changes anythingCould also be an injector leaking fuel back through the overspill pipe, so not getting enough fuel pressure to tell ECU to fire the injectors, this is trickier to find and you’ll need the garage to do a ‘run back’ test to identify which one is the issueyou can also do a reasonable run-back test yourself by disconnecting the electrical plug on the injectors and the downstream pipe of the leak off, crank the engine over and if you see a noticable difference if the flow in the leak off then that the likely problem injector.
it’s also worth considering fitting a new fuel filter as if only slightly blocked this can lower fuel supply pressure and choke the main pump, the pump will be more sensitive to this when its cold as diesel thickens considerably with low temperatures.
I'd also check the condition of the engine wiring loom, especially on its crank and cam sensor connections as these are both critical to the ECU 'synchronising' and injecting at the right point
there should also be a ground / earth connection for the engine bay loom where its secured to the engine with a ring terminal or two and small bolts
these must be clean and tight to ensure the ECU is powered up correctly
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on the diagnostic computer do you see engine speed / rpm when cranking?
OK if you have a cheap OBD scan tool, just one of the generic ones you can get off ebay / amazon often these will have a 'read data' function so you can crank the engine whilst watching this screen to confirm if you're getting an rpm reading
as if the crank sensor is damaged or the ecu has no power then you won't be getting any injection
if you had a faulty sensor, then this 'should' show up as a fault
however this isn't always the case hence I'd suggest checking its function with a scan tool
that is entirely possible
might be worth getting in touch with either of these firms about repair and testing