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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 24212
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have recently fitted a recon engine to my 2012 sprinter.

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hi i have recently fitted a recon engine to my 2012 sprinter. the engine runs on easy start but will not run on its own. we have 300 bar at the rail and fitted new fuel injectors also but still it will not start. I have had a mercedes tech out with there computer and there are no faults coming up.HELP needed we are stumped.
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Hello and welcome to Just Answer

If the EGR valve is stuck open then this can effect starting so try disconnecting it to see if this helps or changes anything
Could 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 issue
you 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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Thanks Matt

Customer: replied 1 year ago.
Hi thanks for the reponse we have fitted 4 new injectors and the are spraying fuel. Egr is moving as it should all wiring has been checked and no faults found.


on the diagnostic computer do you see engine speed / rpm when cranking?

Customer: replied 1 year ago.
Dont have the computer with us now id have to ask the mercedes mechanic. We have changed the flywheel as well.


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

Customer: replied 1 year ago.
When we had the mercedes techs computer plugged in it didnt show any faults do you think it could still be faulty ??


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

Customer: replied 1 year ago.
Ok we will try tomorrow and il get back to you thanks


Customer: replied 1 year ago.
Hi matt we fitted a new crack shaft sensor but still the same. Do you think that the ecu could be damaged. Before the engine blew up the battery was going flat and the van was being jump started alot tge van was playing up and running rough before it blew up which made me think this could of damaged the ecu


that is entirely possible

might be worth getting in touch with either of these firms about repair and testing

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