W203 C220 not starting from cold

[xp2500]

Hi

My C220 cdi 2002 coupe is giving me grief starting from cold.
Its gradually got worse. I have to use easy start spray to get it to start up in the morning.
It just cranks but does not start.
I thought this was due to the high pressure fuel pump as I saw a drip of fuel when it was cranking 2 months ago. I changed this and after a month the problem has returned.

I have tested the battery with a load tester and it performs fine for cold cranking.
I also tried to start the car with a jump start whilst cold and it would not start.

The car runs fine once it has started and performs as normal ( Apart from initially being a bit smokey due to cold start up )
Therefore I think the issue is not related to the battery.

I removed one of the power cables to the glow plugs and tested it with a volt meter and identified that it was not getting power.

I have also run a diagnostic tester on the car ( CDP+ ) and did not find any engine codes for the car.

So I then checked the input wire into the glow plug relay (I replaced the relay last year along with the glow plugs) to see if it was getting a + signal to turn on however my test did not show such a signal. Granted this is not always going to work as the ECU is quite smart and I might not be able to test that way.

Would anyone be able to provide me with a logical next step into isolating or diagnosing my issue.

 

[mersum1es]

It's very common culprit; low fuel pressure. Most likely you have leaking return lines/o-rings (do you see air bubbles in clear lines). Next thing to check is injectors, their tank line leak and electrical correction values via SDS. Last thing is fuel pressure control valve which may be jamming or leak.

These inline engines starts pretty well even some of the glow plugs have failed, you should measure resistance of the plug and wires (unplug connector from relay module). Broken plugs sometimes break module too.