Sharing solved problem
Thread Starter
Junior Member
Joined: Jun 2014
Posts: 49
Likes: 3
SL600, S550, GLS450
Sharing solved problem
I wanted to share what I found to be the problem with my SL600 as I likely would not have guessed it without the helpful advice of someone with a lot of Mercedes experience. It saved me a lot of time and money.
The issue began as rare misfires. I could feel them when driving maybe once in a month. OBDII codes confirmed misfires on 10 out of 12 cylinders.
One day the car would not run. It would turn over and start, then sputter/die. I looked around online and the most likely/common issue was the ignition coils, transformer, or crank position sensor. Most people ended up spending a of money only to chase the problem.
In my case, it ended up being the fuel pressure sensor. This threw me off initially because there was no code thrown. Even my old mustang's OBDII let me know when the fuel pressure sensor went out. The reason I thought this would be worth posting is because a computer diagnostic will not flag the problem. The sensor communicates directly with the fuel pump but nothing else. If the pump/sending unit is operational, the problem won't be detected at a glance. Even a voltage check of the sensor may not always indicate a bad sensor.
The best way to check this is with a fuel pressure gauge. A faulty pressure sensor will keep the fuel pressure either at 8 bar (wide open) or 0 bar (shut). At 8 bar the car will still run, at 0 bar the car will still start for a few seconds. Either way, it may be misdiagnosed as an ignition issue as cylinder misfires will be the primary symptom without obvious indication to the fuel system.
The mechanic that explained this to me had spent a lot of time and money before he found out that the fuel pressure sensor was to blame. The only way to know that the sensor stands alone to the pump (except for a fuse and relay) is by looking at a wiring diagram.
Hopefully this is helpful to someone else and saves them some time and money as it did for me.
The issue began as rare misfires. I could feel them when driving maybe once in a month. OBDII codes confirmed misfires on 10 out of 12 cylinders.
One day the car would not run. It would turn over and start, then sputter/die. I looked around online and the most likely/common issue was the ignition coils, transformer, or crank position sensor. Most people ended up spending a of money only to chase the problem.
In my case, it ended up being the fuel pressure sensor. This threw me off initially because there was no code thrown. Even my old mustang's OBDII let me know when the fuel pressure sensor went out. The reason I thought this would be worth posting is because a computer diagnostic will not flag the problem. The sensor communicates directly with the fuel pump but nothing else. If the pump/sending unit is operational, the problem won't be detected at a glance. Even a voltage check of the sensor may not always indicate a bad sensor.
The best way to check this is with a fuel pressure gauge. A faulty pressure sensor will keep the fuel pressure either at 8 bar (wide open) or 0 bar (shut). At 8 bar the car will still run, at 0 bar the car will still start for a few seconds. Either way, it may be misdiagnosed as an ignition issue as cylinder misfires will be the primary symptom without obvious indication to the fuel system.
The mechanic that explained this to me had spent a lot of time and money before he found out that the fuel pressure sensor was to blame. The only way to know that the sensor stands alone to the pump (except for a fuse and relay) is by looking at a wiring diagram.
Hopefully this is helpful to someone else and saves them some time and money as it did for me.
Last edited by aeb28; Aug 19, 2014 at 01:39 PM.
Senior Member
Joined: Feb 2005
Posts: 254
Likes: 17
From: America
CL600 2003
Same thing happened to me
https://mbworld.org/forums/m275-v12-...elaration.html
https://mbworld.org/forums/m275-v12-...elaration.html
Newbie
Joined: Oct 2012
Posts: 7
Likes: 0
From: Texas
2004 clk500, 2009 ML550, 2009 CL600
same problem
I am at mechanic the fuel pressure is at 4 bar with engine on. What could be cause. Fuel pressure sensor or fuel regulator. Where are they located? Do you have number of mechanic who worked on your car. What is normal fuel pressure for m275 v 12 engine?
