Russell West

It started doing this suddenly. Every time the ignition is turned off and restarted, the engine cranks for 8 seconds before catching and running perfectly.

Have a p0002 code for fuel pressure. Seems like the the pressure regulator isnt holding pressure after shutdown

This means a new hp fuel pump, or if something else to look for? The HPFP has a regulator built in

mercjames

Probably the HPFP but there is also a fuel pressure regulator sensor on the fuel rail. I would think the ECU would give a specific code for the sensor if it was the problem though. I found this document referencing a fuel issue on the c250 but I'm not sure if you are experiencing these issues. https://static.nhtsa.gov/odi/tsbs/20...51540-9685.pdf

I feel like maybe they released this software though to cover up the fuel pump failures and make them last a little longer but it's worth looking at.

Russell West

Expansion on the problem. Fuel pressure was down at 50psi even after the car started. Idle was fine and the car could be driven around but power was low. Ran fine otherwise.

If let run long enough, spiking the RPM to get the fuel pump turning faster, after 20 minutes the car would run and start great. 20 mins every time. Like there was air in the high pressure system that bled out. Takes awhile.

It continues to start and run great for an hour or so afterward. Next day it's exactly the same. Low pressure and takes 8 seconds to start.

Replaced the fuel pump, it's a little better but still the same problem.

Seems like its losing pressure somewhere. Maybe through leaking injectors?

Is there a return line on the high pressure system or possibly leak back through the pump?

Russell West

Fuel pressure is
~50psi when starting cold and after startup
~1000 psi when running after it
~200 psi after shutdown and keeps dropping slowly afterward

mercjames

Considering you replaced the pump it shouldn't be losing pressure unless there is a problem with the fuel lines or injectors..I would think. Your hpfp may not be getting enough fuel to build pressure which could be caused by the low pressure fuel pump and filter assembly. I've attached some diagrams from EPC of the fuel system.

Russell West

Thanks for the diagram! I'm leaning toward fuel injectors.

Engine has good power after 30 minutes of driving. Everytime. And low pressure fuel is always there quick. Longer the engine stays off the worse it runs. Feels like rail gets air in it.

Russell West

After car sit for many hours, car has the long crank condition and fuel pressure stays at 55psi for 10 minutes. Runs and idles smooth but no power.

After bumping Rpm up and down a bit, I see pressure fluctuate up to 300 but drops back down when let off gas.

Keeps improving then after running for 30 minutes pressure stays around 1000+ and power is solid

After shutoff, restart is quick and power still there.

So really seems like fuel is leaking out or back somewhere. No exterior fuel smells.

mercjames

Sorry for the late reply. I did not see your reply notification. I think if you can't find any issues with the fuel system you should look into the cam adjuster issue with these engines. MB is warrantying them now for 2 more years or so. These symptoms sound like the cam adjuster issue. The car starts fine after being started recently but fails to start or is hard to start after sitting for awhile. If you get the cam adjusters replaced also replace the secondary pcv valve under the intake as it leads to fuel in oil which causes the cam adjusters to fail to begin with.