Hi all been a member for sometime just like reading all info that you guys write.
OK ive got a clk280 2009 model petrol and have a starting problem .Had the car for 4 years
some days the car is spot on but some days its not , starting from cold most days its first turn other days its not very long cranking , and it does this hot or cold , ive fitted a new CPS and a new air flow meter no codes or lights have ever come up.
when running the car drives perfect no problems , its just the starting.
just wondered if anyone has come up with the same problem or could help me out,
many thanks for your time John

 

Hi John, welcome to the forum. So, you are saying that the starter does run and the engine does rotate, but it does not "fire"? That does sound like a CPS problem. Did you buy a genuine MBZ or Bosch from a reputable source?

 

I got one from Amazon and chased my tail for over a month, and $500 in tows before I replaced it with a good part from a reputable seller. Auothaus.

 

Hello and thanks for reply , the cps was not MB parts but I have ordered a MB part after reading about the problems people have had .
As soon as i receive the part and fit it I will up date , many thanks for your time John

 

OK fitted new cps MB part ok for a few days then the odd time not .
In looking into problem more I have noticed that if I turn on the ignition to prime the fuel system and then back off again , then back on and start the car it has not missed starting once .
don't think its a fuel pump problem but more a fuel pressure regulator not holding pressure in the fuel rail.
Any help would be good thanks John

 

Check pressure - there's a Schrader valve on the fuel rail.

 

OK ive checked the pressure .
turn on the ignition and the fuel pressure goes up to 55psi then drops off straight away
when i get the car started the pressure holds steady at 55psi with not much movement , I believe my problem is the fuel pressure regulator in the fuel tank which is where my fuel filter is , what do you think

 

The pump is in the right side of the tank, the sender (which contains the regulator) is on the left.