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Fuel pressure issue

5972 Views 14 Replies 5 Participants Last post by  robint
Hey Justin here. I am having a fuel pressure problem in my 2005 slk 350. I was sitting at a stop light and the car started idling rough and began to stall. I got it into a parking lot turned it of and it wouldn't restart. I took the fuel pump out of the tank hooked it up to a twelve vault battery and it ran fine. I switched out the fuse and relay and I still have now fuel pressure. Any ideas would be much appreciated!
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I assume you've checked all fuses and you're measuring with a fuel pressure gauge... Was the fuel filter replaced per the service schedule? Reason for the ask: the pressure regulator is in the filter.
Yeah, although I have just ordered a new one. It is $91 to replace the fuel pressure sensor and $108 to replace the entire fuel filter assembly. I have to say it is a bit crazy how tough it has been to obtain the fuel system parts. None of the MB dealerships in Colorado stock these parts nor are there any O.E.M. equivalents.
What was your fuel pressure measurement value at the fuel rail?
Isn't the fuel pressure sensor just for EVAP leak testing?
There was 0 reading, so I disconnected the fuel line at the fuel rail and had absolutely no fuel traveling to the injectors.
I checked the voltage at the fuel pump wiring harness and was getting about 10.5 volts and a 12.3 reading at the battery, so there is almost a full 2 volt drop. Does anyone know where I may be able to obtain a wiring schematic for the fuel system so that I can perform a drop test?
More info from Justin:

Just to recap I was at a red light and the car started to idle rough and the check engine light came on. I attempted to accelerate and had no power. I was able to pull into a parking lot and turned the vehicle off. I was unable to restart it. I hooked up the O.B.D. And the error codes were two multiple cylinder misfires, cylinder 1, and cylinder 5 misfire. I changed the fuel pump fuse, the relay, removed the pump made sure it was working properly, and I just installed a new fuel filter/ pressure sensor assembly. Now the car starts after a couple of tries but revs up to around 1200 R.P.M. And shuts off. I disconnected the M.A.F.S. To see if that was the issue but it had no affect.

The vehicle is no longer under warranty so if anyone has any suggestions they will be much appreciated.
Did you resolve the voltage drop yet? That is a good starting place.
Yeah voltage is good. Car shuts off after 2 to 3 seconds.
I already put a new filter on.
And you still have no fuel pressure at the rail? Or are you saying the fuel pressure drops at the rail after 2-3 seconds?
Just wondering why you would suspect fuel pressure if only 2 cylinders are showing codes - fuel pressure and fuel pump issues are not common on R171 models as far as I know.
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