Fuel System Info Needed__Gas Not Returning to Pump
Newbie
Joined: Jun 2011
Posts: 7
Likes: 3
w205 coupe
You need to check your pump integrity & filter & all balance lines for blockage or leak. Also check breather lines to the EECS system (evapourative emissions control system). Older cars with the external filter maintain a single pressure line to the front at 3.8 bar while the pressure regulator in the filter dumps excess fuel back to tank. Update your profile to include model year of your car.
I no longer post pump side as Benz is all over the place with this.
I no longer post pump side as Benz is all over the place with this.
Newbie
Joined: Jun 2012
Posts: 11
Likes: 0
06 c230 sport
I have this problem. I recently replaced the pump, sending unit, and fuel filter. From what I can tell, the sending unit is a motive flow pump. Basically it uses the returning fuel pressure to suck more fuel out of the sending-unit-side fuel tank and sends it to the fuel-pump-side fuel tank. I'm going to put a fuel pressure gauge on the return side tomorrow but I was wondering if anyone with the shop manual could tell me if they list a return-side fuel pressure spec in the book?
MBWorld Fanatic!
Joined: Jun 2002
Posts: 7,265
Likes: 169
From: So. Oregon Coast
C230 Sport Coup + 2006 W164 ML350 + 99 Ford Escort RIP
Yes, all these years later, and I find this thread. Did he ever solve the issue?
Tomorrow, I tackle the pump replacement.
Tomorrow, I tackle the pump replacement.
I have this problem. I recently replaced the pump, sending unit, and fuel filter. From what I can tell, the sending unit is a motive flow pump. Basically it uses the returning fuel pressure to suck more fuel out of the sending-unit-side fuel tank and sends it to the fuel-pump-side fuel tank. I'm going to put a fuel pressure gauge on the return side tomorrow but I was wondering if anyone with the shop manual could tell me if they list a return-side fuel pressure spec in the book?
Member
Joined: Nov 2007
Posts: 171
Likes: 1
From: ontario, Canada
C230 COUPE 2003 M271
i havent had the problem of fuel not returning to the pump/tank but to me it would seem more like a fuel pressure regulator problem which is built into the fuel filter.
Super Member
Joined: Jan 2015
Posts: 920
Likes: 46
From: Worcestershire UK
W124 260E
Do these engines have a filter in the return pipe from the injection system ? For fuel returning to the tank.? Like the old m103 engines If its blocked fuel wont return to the tank. Just an idea
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MBWorld Fanatic!
Joined: Jun 2011
Posts: 1,494
Likes: 131
From: Cape town
not a merc
No. and I have never seem a return filter on a M103 either. An easy way to check if your return is blocked is to check fuel pressure at the rail if ìt is higher than the spec it means your return is restricted.
Newbie
Joined: Dec 2017
Posts: 1
Likes: 0
2005 E55
Anyone ever solve the Gas going only to one side issue?
I see a very enthusiastic reply to a post from Splinter from long ago, but the post appears to be empty. I have replaced both the pump module and filter module with the new upgraded design from Mercedes. I think my problem lies in the routing of the fuel lines between the tank sides. It looks like there are 2 extra lines (1 fat, 1 skinny) that i'm unsure where they go. I think the fat one clips to the top of the fuel pump module side, but the skinny one I have no idea. Looks like it is the one with the one-way valve in it? Any help or a routing diagram for the lines would be greatly appreciated. Or perhaps whatever miracle cure Splinter came up with if someone can locate the post. Thanks in advance.
Newbie
Joined: May 2019
Posts: 1
Likes: 1
2003 mercedez benz 240
Trouble after replacing fuel pump
Please call me Glyn - I'm sure it's the darn pump. They usually seize. I'm sure you will lick this one. The job I did on a friend's high miler was totally successful & still fine 3 years later. Just replaced both unit's - passenger & driver's side at the suggestion of my friendly service manager who maintains when one side goes, the sender on the other side is usually not far behind. I did not replace anything else. All hoses etc were fine. If you just want to replace the pump side that's fine. If the other side packs up at least access is relatively easy & you know how. Sorry for misleading you up front - it was a genuine & unfortunate mistake - good luck 
MBWorld Fanatic!
Joined: May 2017
Posts: 2,290
Likes: 434
C320
On the driver side as well for balancing. Could that be the case with ours? He had it started for a few minutes and then it just died out that’s about the best we’ve gotten I would really like your help. My husband just replace the fuel pump and for some reason we are having trouble getting the gas to get through to the carburetor. I’m inside looking for help on my phone and he’s out there still trying. I read that there’s other things that need done On the driver side as well for balancing. Could that be the case with ours? He had it started for a few minutes and then it just died out that’s about the best we’ve gotten
Newbie
Joined: Sep 2019
Posts: 1
Likes: 0
2002 Mercedes C320 Wagon
Same issue
Diagnostic code
Just replaced the fuel filter recently and new fuel pump, on passenger side. Works great for about 2 weeks then dies. Look into the fuel tank with the pump on passenger side, and tank empty of gas. Gauge shows I have a quarter tank. But I did a custom hose job after breaking one while replacing the fuel filter, so I bet that is where the problem is now. From computer troubleshooting ... user error lol. Anyway I was real proud of my custom rig on the fuel line till now. I used a 5/16" to 1/4" hose reducer to replace the broken right angle adapter I broke. Checking today it was still in place but from the previous posts i bet the pressure is off...if it is pressure regulated. The only code I got was DTR an p410 secondary air injection which is not the cause of this fuel system issue.
Last edited by Stephan Bayer; Sep 4, 2019 at 07:38 PM. Reason: Add screenshot
