Fuel System Info Needed__Gas Not Returning to Pump

[MM Alexander]

Hello All, I'm chasing a fuel return problem on a 2002 C230K, my fiancee's car. \ Saturday, she's less then a mile from home and the car dies. I go to try and road side diagnose and determine it to be a fuel issue. It would start for a second or two then run out of fuel and die. I check all the fuel filter connections (had just performed a maintenance tune up with plugs, new filter and Sea Foam treatment the previous weekend)) all seemed fine. Decided to have it towed home ($55.....What a rip-off) for further diagnosis. I decided to first check the pump itself by powering it directly from a 12 volt source. It powered up but still car wouldn't start. I then continued to try to find info about the car on the interweb. I came across various info about the CPS being a culprit to such antics as I was experiencing. So I had her get one the other day, install it and still a no start. Oh well, the car has right at a 100K so I count it as a needed maintenance item and get back to the fuel system. I pull the 2 sections out and see that the fuel pump itself is housed on the passenger side with some lines that connect it to the housing on the drivers side of the car. I inspect the se-up even closer and notice that the pump side of the tank system is totally dry while the drivers side is full. I take a small bottle and use it to siphon fuel from the drive side to the pass side where the pump is located. Once the pump side was full I decide to try and start it. Low and behold it cranks up and runs ......until the fuel pump side is sucked dry So does anyone know/have info on the fuel system in these cars? I mean, what creates/controls siphon and or return? I figure this is a return less fuel system..I. E. no return line to the tank from the fuel rail. but something must control fuel staying and or being balanced between the two tanks, right? A diagram or just explanation of the fuel system would work wonders in helping me diagnose this problem. Any and all help is appreciated and welcomed.

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[Glyn M Ruck]

Where are you? Your fuel pump and sensor unit should be under the drivers side (LHS) back seat & the second level sensor under the passenger side. Check all wiring & piping & both sensors to ensure fuel balance between the two sides. You might have sensor failure or an air leak on one side

See pics

[mleskovar]

This sounds like a bad transfer pump or hose. I haven't worked in that area but have read on this forum that the gas tank is split in two halves and the pass side transfers fuel to the the driver's side of the tank to keep them balanced as fuel is consumed. Do you have the two sides mixed up in your post? I also believe there is a fuel return line that routes through the charcoal filter (not sure about that)?

[MM Alexander]

I'm in the States...Houston, Tx. to be exact.
I assure you, the pump is on the passenger (right side). I've attached pics of both.
Now that we've cleared that up (and maybe someone should ask/recommend that guy update/fix his site...Pump is on the Pass Side...Tool to remove rings? Flathead and a few taps of a hammer and it turns freely) any idea what the problem could be? Is there a fuse for the purge canister? If not, how is the purge system activated/de-activated?

EDIT
Went back outside and took some pics just to show I'm not a total nut case

[MM Alexander]

Funny you mention transfer pump. I was outside earlier (once I tracked down the issue) contemplating throwing an in-line pump in the tank and have it pump from the driver side to the passenger side. I was concerned with "dead heading" the pump by running it with no type of regulator.
Any idea where the Daimler places the transfer pump in these cars?

[MM Alexander]

Just looked over EPC and Mercedes shows the pump as being on the passenger side of the car as well. I looked over the whole schematic but it does not show a transfer/equalizer pump
More searching is in store I guess.

[mleskovar]

There are two pumps. One is fuel delivery and one is balancing. Both have level sensors incorporated. They call both of them 'fuel pumps' on the on line catalogs. The on the driver's side lists at $482 and the one on the passenger's side lists at $325 so I 'think' the main fuel pump is on the left/driver's side. Like I said, I haven't worked in this area other than to change the fuel pump filter and lube the parking brake fulcrum. Maybe the level sensor is out on one of the sides and it's not balancing? What does the fuel gauge show (you know it's only half full)? Also...if the gas fill is allowed to go beyond the 'full' point (topping off) it is possible to saturate the charcoal filter and disturb the system.

[MM Alexander]

There is only one pump on this car. It's on the passenger side
I've attached a pic of what is in the drivers side compartment.
Also, when checking EPC it only shows one pump but 2 fuel levels.
The fuel level on her car shows a 1/4 tank which is in-line with what it should have in it.
I read a post from 2002 that stated

By the way - both sections of the pump (one side transfers fuel from left tank to right tank, and the other side delivers fuel to the engine) run off a single electric motor. The second part of the two-piece pump assembly is the fuel pressure regulator/fuel filter assembly.

Sounds plausible as this is how her car is set up (contrary to what may be posted on the interweb that says differently). I may just buy a new pump assembly (her's may not be strong enough to do both jobs of transfer and pump.) as that seems to be the only thing that makes sense.

[splinter]

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[MM Alexander]

Splinter

THANK YOU!!!!!!!
Not just for me, but for the others who may see this in the future. The mis-info created by that DIY site is spread far I see. Your PDF attachment shows exactly how my girls car (and probably every other w203) is set-up.
Her car must have a bad pump (secondary part of it at least) or a clogged in the line that feeds to/from the drive side unit.
Thank You Again!

[mleskovar]

Originally Posted by splinter

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Thanks!

[Glyn M Ruck]

Originally Posted by splinter

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Thanks Boss - it's funny I was going to suggest you for a schematic right up front

[Glyn M Ruck]

Originally Posted by MM Alexander

I'm in the States...Houston, Tx. to be exact.
I assure you, the pump is on the passenger (right side). I've attached pics of both.
Now that we've cleared that up (and maybe someone should ask/recommend that guy update/fix his site...Pump is on the Pass Side...Tool to remove rings? Flathead and a few taps of a hammer and it turns freely) any idea what the problem could be? Is there a fuse for the purge canister? If not, how is the purge system activated/de-activated?

EDIT
Went back outside and took some pics just to show I'm not a total nut case

I don't think that you are a nutcase & I'm pleased you've sorted the issue. I too hate misinformation. That's why I asked you where you were. Just to clarify. Not all cars are set up like Splinter's schematic. My pump is on the passenger side of the car and I'm in a RH Drive country so that's the LHS of the car. Why some are one way and some the other - who knows - idiosyncratic Benz. Maybe due to prevalent camber of roads. There is only 1 pump.

BTW. I've been down this road with a friends car. Benz recommend replacement of both units simultaneously.

[Glyn M Ruck]

Interestingly enough I see that your pump is a Pierburg - mine & most RSA cars are Bosch. Good to know. If my pump ever becomes noisy I will try a Pierburg. VW use Bosch & Pierburg interchangeably as well

[MM Alexander]

Mr. Ruck,
Thank you for the response/reply. I should have stated I bet "most LHD" (if not all) w203 models are set up like hers
I too think I'm just going to get a pump as I can find nothing wrong with anything else in the system. No clogs , no kinks, holes of any kind in/on the transfer line. It's said to be a 2 piece design so I'm just thinking the suction side (for transfer) is too weak to keep up. I'm going to get a siphon (and some more damn rubber glove's! As the petro has ruined a box of them) and drain the tank, I'm sick of working in gas! I'm then going to investsigate the system one last time (for good measure) before I have her order a pump. Well I should say, assembly as I have found only 1 place that sells just the pump and that was only a few dollars less then the whole assembly.

[Glyn M Ruck]

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

[Glyn M Ruck]

BTW - Be careful to put the damping pad back in place properly. Some people are very sensitive to pump buzz in the car & this helps.

[C230 Sport Coup]

MM,
There's an old rule of repairing anything...
that is....go back to the thing you did last.

If the car was running fine before you decided to do a little maintenance, and then had problems afterwards, there are 2 possibilities.
a. You made a mistake- Go back to the repairs you made, and be absolutely certain you
didn't make a mistake or get faulty parts. Possibly connected the fuel filter back wrong?
I could see that happening, with 4 hoses, which is why I did mine one at a time.
Or possibly one of the pumps was damaged if you didn't clamp the hoses, and allowed air to get in.
For me, I had no issues, while others did get a CEL.

Once, I did a tune up, and got a bad rotor (back in the day). After I put everything back the way it was when I started, everything was fine, then did one part at a time to find the defective one.

or
b. It's just a freak coincidence, but usually like 90%, it's something that was done the last time you did something. Or a bad NEW part.

While it's often tempting to do many things at once, it also can make it difficult to
determine which thing was the cause of the problem.

These rules apply to cars, computers, whatever.
Do something, test, make sure it works, or doesn't or is at least the same before
progressing to the next thing. Though it can be more time consuming, and other times I do take the shotgun approach and cross my fingers. Kinda a gut feeling on which is the way to go in any particular situation.

Now all that said, please don't be offended if my advise seems obvious.
I was a Field engineer for many years, and this type of logic served me well while
under great pressure to make things work on a schedule, all over the world.
And also in repairing my own stuff, like cars, and computers.
Before you look at anything else, go back to where you started.

It's too easy to introduce new problems when you start digging into new things, and there's always the chance of getting bad parts too, even when they're "new", or
in my case, 'back in the day' many of the parts I was given to repair stuff
ws dubious. Always good to start with parts that are known to be good, meaning used, or tested
in another unit.

Since you already have problems, there's no way to know if the new parts are introducing new issues,
or are defective OR even the wrong parts. This is the worst case senario for a repair.
Sux. Hope you get it soon. But if the pump was fine and then went bad after replacing the filter, you must have done something....

Just my 2 cents.

[Glyn M Ruck]

+1 all the way. Maybe gave the pump a dose of dirt when changing the filter - If he means he changed the fuel filter.

[MM Alexander]

C230, I appreciate your response and input but let me give you a bi of feed back to help out:
I am a field engineer with GE Wind Energy division (Supervise and Inspect the Erection/Construction of 1.5 Mw Turbines). I've worked as a Field/Installation Tech of some type since I was 19 (39 now). My car back ground goes from Professional/Competition Car Audio to 60Kv power distribution centers. I had part of the contract with HP for the renovation of their Data Center (Houston). I've ran/terminated more Fiber and Cat 6 then most people will know exist!
I am thoroughly entrenched in custom car modification (I'm a Hot Rodder! ) My garage currently houses a 600 HP 95 Single Turbo Charged Mustang, 06 SIngle Turbo GTO and a 03 Suzuki Gixxer (too busy to build a turbo kit for it ), all built/modified in house. I've been tinkering with cars/bikes since I was 15 or so.
Now on to the current issue. For the maintenance tune up on the car and possibility of problems from such. Changed plugs, changed filter, Sea Foamed treatment for motor.
Plugs, no rocket science there. Fuel Filter, I keep seeing how people say you could put it on wrong. I find that impossible unless you're trying extremely hard to do so. I say this because the hoses to and from the regulator are of different sizes. The to/from the fuel pump are form fitted and pretty much lay in position of where they go. Just the fact that the engineers designed the regulator hoses of different size makes me say you HAVE TO BE TRYING to screw that up, lol.
As said in my previous post, the car runs drives just fine....Well as long as you finda way to keep fuel on the pump side of the tank . The car drove 10x better the week following the tune up (gotta love Sea Foam!). She says the car cut off on her Thursday but came back on afer she pulled over to the side. Didn't have a problem again until Saturday, when it finally stopped.
I'm going to investigate the pump/fuel set-up a bit more today. I see nothing wrong with it thus far so I'm fairly certain I'll simply need to order a pump assembly.
C230 Thank You Sir (again) and Mr. Ruck...... I meat Glyn

[C230 Sport Coup]

Wind Turbines eh? Well, that might be the right biz to be in with the new
administration pushing alternative energy.
I've been trying to see if I can't get into that myself with my background in SCADA systems, and PC networks. I worked for Landis & Gyr for a number of years, and commissioned many substation RTU and master station installations + did training for pretty much every utility you can name in the US, + Canada, Mexico and Thailand.
I would guide the electricians in hooking up all the automation stuff, and then find all their mistakes,
and make them fix them...then once the system was up, I could train the users and engineers and help them build their database and schematic diagrams (Clickable).

Then I went to PC related stuff, got tired of traveling, became a sysadmin
and techie guy. But these days, most of those jobs can be offshored except the actual desktop support people. But thats gotten to be such a thankless job.
(Though I'd be happy to get it...

I'm curious about your POV on the whole power systems biz these days, where it's headed, and job availability, pm me if you care to.

[Ruberli]

Hi, i have a same problem, only empty right chamber, somebody help me?

[Russell Ormerod]

Check your fuel delivery, then renew fuel pump and filter

[Ruberli]

I think it is a common problem, I've changed the fuel filter and the problem persists. believe that the problem is the fuel pump? someone has had the same problem?

[Glyn M Ruck]

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.