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gomi_otaku
gomi_otaku, Technician
Category: Mercedes
Satisfied Customers: 3439
Experience:  VW Technician, VW FastTrack, VW Academy, VW Certified
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Fuel Pump Continuously Shuts off When filling up. Recently

Customer Question

Fuel Pump Continuously Shuts off When filling up. Recently Replaced P/S Sending Unit.
Submitted: 9 months ago.
Category: Mercedes
Expert:  Lou P. master tech replied 9 months ago.

Hello, my name is***** and i will do my best to assist you.I am going over your story now and will reply back soon with some info,thanks!

Expert:  Lou P. master tech replied 9 months ago.

sorry i took so long, i wont be on too much today, ill chat with you later about this issue.

Customer: replied 9 months ago.
Ok
Expert:  Lou P. master tech replied 9 months ago.

ok so i am not sure if we are on the same page any more, the fuel sender has nothing to do with the fuel filling nozzle shutting off. so do you know if replacing the sender helped the fuel level gauge at all?

Customer: replied 9 months ago.
It didn't help the guage at all to my surprise. The stored code read as right side sending unit malfunction so I finally got the right side replaced. I was giving you a status update overall since you know the history on it. As far as the pump shutting off at fueling. I don't know what the issue is. I blew air into the canister and the purge valve is practically a new part on the vehicle (2yrs old at least.) Is there a valve in the fuel neck? Should I replaced the charcoal canister? I've been dealing with this since forever and I hate dealing with it in bad weather because I have to stand outside and pump gas.
Expert:  Lou P. master tech replied 9 months ago.

did the code go away for the sending unit?

Expert:  Lou P. master tech replied 9 months ago.

as for the charcoal canister and the fuel system, it has to be one of the 2 canisters.

the purge valve in the engine bay has nothing to do with the system. just the canisters because it looks like your model does not have a canister vent valve that i can find.

this fuel system is really hard to get some solid info on, if i was near the car it would be easier lol.

Customer: replied 9 months ago.
the code went away for the fuel unit. I did read something online saying you can't replace just one, you have to do both?? So i only have one canister correct? VIN= WDBHA28E5VF509869
Expert:  Lou P. master tech replied 9 months ago.

You dont have to do both, only on a later model they updated the sending units so you needed to do them together. not on yours from what i recall., ill look at the parts catalog again for the fuel tank.

Customer: replied 9 months ago.
oK, then why would the fuel gauge still show empty at times. it never fixes itself either. I have to reach behind dash and unplug the cluster for 2-3 minutes then it registers correctly for 4-5 start ups from the key. then it completely drops down to not even moving. i've even replaced the cluster thinking it was initially the cluster itself 2 years ago. (used replacement)
Customer: replied 9 months ago.
Still there?
Expert:  Lou P. master tech replied 9 months ago.

lets stick with one issue at a time, if we jump back and forth it will take longer to figure out what is happening.

so lets stick with the fuel filling issue since that is a pain for anyone to deal with. sorry i have not been on as much, very hectic right now for me.

i pulled up the parts catalog earlier and found a check valve in line with the canister under the car. not sure where it located but its something that may have a effect. ill be back on in the am.

Customer: replied 9 months ago.
Ok
Customer: replied 9 months ago.
Ok
Customer: replied 9 months ago.
Are you available today?
Expert:  Lou P. master tech replied 9 months ago.

i will opt out at the moment and come back if there are no other responses. sorry i am not able to be on as much as i would like at the moment.

Customer: replied 9 months ago.
I understand
Customer: replied 9 months ago.
Waiting on a response.
Customer: replied 9 months ago.
Hey, i tried to pump fuel and it poured out of the area i removed the hose from. Gas everywhere.....
Customer: replied 8 months ago.
Well, any idea why my fuel guage continues to stop working even after I had the fuel sendinf unit replaced??
Expert:  gomi_otaku replied 8 months ago.

Generally when you see a problem like this it is your charcoal canister for the evaporative emissions systems. When you fill your tank, the gas going in pushes air out. It should go out through a vent valve, through your charcoal canister, which absorbs the gas fumes and allows filtered air back out into the atmospherre. When your charcoal canister gets clogged (usually from topping up the tank repeatedly, but sometimes from a faulty gas pump) the air instead tries to push back up the filler neck against the gas coming in, shutting off the pump from the sensor at the nozzle.

Customer: replied 8 months ago.
Well, i figured this part on my own by replacing both charcoal canister and expansion tank. However, i have not figured out why my fuel guage continues to stop working intermittently. It just drops down to empty on any given day. I previously thought it was the fuel sending unit so i had it replaced and the problem still persists.
Expert:  gomi_otaku replied 8 months ago.

Have you checked the pins at the connector to the cluster- make sure they are not spread and are able to get good contact at all times. If the cluster is changed, and the fuel sending unit, that only leaves the wiring- but since you can get it to change by unplugging it, it would seem that it MAY be isolated to the connector.

Customer: replied 8 months ago.
The connector is part of the harness. How would I fix it?
Expert:  gomi_otaku replied 8 months ago.

I would just start out by inspecting it- if necessary to repair, you can get new wire ends that plug into the connector, and splice them farther back into the harness with heat shrink butt connectors.

Customer: replied 8 months ago.
Is there a part number for the wire ends that plug into the connector? This is the only part of the cluster malfunctioning.
Expert:  gomi_otaku replied 8 months ago.

You would have to get these replacement wires from the dealership. The ETKA parts film will allow them to look at the cluster, this will tell them what connector is on the backside, and what wire ends go with it. There are hundreds of different wire ends in the VW/Audi system, and different thicknesses of wire as well, from half a millimeter up to 5mm.

Customer: replied 8 months ago.
This for a Mercedes-Benz
Customer: replied 8 months ago.
It seems like the fuel guagr gets wacky whenever the fuel falls below half of a tank. It quickly starts to journey to register empty after it accurately registers half tank. Sometimes if i start the car with over a half of a tank the guage will stop workibg altogether after 7-10 start ups of the engine itself.
Expert:  gomi_otaku replied 8 months ago.

Sorry, I meant Mercedes-

If you have a new sender, and a new cluster, wiring is the only link between them.