Difficult morning start
 

We have a 2006 Diesel S 40 2lt with 240K Km. The engine seems to be running perfectly, the engine doesn't use any oil. Recently serviced. Just had a new battery replaced. First thing in the morning the car is really rough starting and has to be cranked several time before the engine catches. No smoke. Any help would be appreciated.

Check you have decent battery voltage, then fuel. When was your last fuel filter change?

glow plugs
 

First suspect in diesel starting are the glow plugs. On a 940 it takes 3 of these or more out to stop it. You can test by (briefly) attaching to 14V, it can also be done by checking the resistance. If the glow plugs are ok next stop is the glow plug relay.

jor

No smoke suggests no fuel, if the glow-plugs were failing I'd expect a lot of smoke on start up?

We have a new battery and run the car regularly on long enough trips to keep the battery charged. The fuel filter was changed 1 month ago.

Once the car has been started for the first time it generally starts ok, but not as fast as it used to but on the first crank. The engine is running well, no misfires or spluttering. The start is rough the whole engine block really shakes. I read that the Fuel Pressure Regulator can give trouble, but would this only be a problem on the first start?

Could it be fuel draining back to the tank being caused by air getting in somewhere??

Did you do the filter yourself?

Ahh, I'm assuming this is a common rail engine. Sorry I'm not familiar with the S40 or what's specifically under the bonnet.

Maybe having it plugged in to a diagnostic machine for a cold start would be the way to go...……... Observing RPM signal and fuel pressure reading.

Something else for you to consider...as you look at the front of the engine, on the inlet manifold, check the shut off throttle is reopening, ready for the next start, after you switch off the engine. If it is sticking in the closed position the engine can't/won't breath. As it's made from plastic it deforms over time so a new replacement is the best option. The reason it eventually starts is because the shaking releases it.