Given your description it may be 1. Glow plug(s) not functioning, or 2. Glow plug controller not functioning.
The glow plugs heat during the first couple of minutes to ensure smooth running. If they do not heat the engine will still start and run, but there will be noticeable roughness.
In...
I’d take it back for “further investigations” as you have engaged a shop and report the scan codes here.
How many miles?
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It is better to scan the vehicle with a tool designed to read the MB coding. Often the typical generic readers only provide a general direction of the problem.
Taking it to a dealer will cost an hours worth of diagnostic time. You may find a local independent shop that can scan and diagnose...
Misfires at cold startup certainly point to glow plugs.
The long cranking points to fuel. When was fuel filter last changed? Generally they are a 20,000 mile maintenance item.
Have the air filters been checked? This is another area that can impact operations.
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You need to have the car scanned and report any codes found.
There’s too many possibilities to properly begin any diagnostic.
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As I recall doing this on my ML I did need to remove the bolts holding the resonator on the engine. The lower end of the resonator connects to a hose so there’s room there.
I found that putting things back together was the challenging part. The O-rings, when new, make for a tight fit. The...
You could try cleaning the reader itself. Buy one of those lens cleaning disks with the little brushes.
Could just be enough dust on the laser that is to blame.
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”After a recent ECU/emissions update”
I recall a similar discussion on the MB UK site. Same observations.
I’m suspecting that the update was designed in response to the VW/Bosch debacle.
Did you request the update? In my experience with MB the software is not automatically updated unless...
The schematic for my ‘08 OM642 (US) shows a BAS travel sensor mounted below the master cylinder.
Not sure if this means anything for your situation, but figured I’d offer it.
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Agree with using the centered spring compressor.
I did similar to what you are suggesting and had quite the difficult time of it.
To make matters worse the springs I received were incorrect. I had the correct set installed at the dealer and returned the wrong ones for a refund.
Buy, borrow or...