VIPclk320

Hey everyone, I'm having some major issues. This is how it goes.
Last week I was in the middle of no where and needed has so I pumped 2 gallon of some cheap gas(vallero) because that's all I could find. The next day I pumped about 4 gallons of chevron and later that day I pumped a full tank of chevron again before I drive to a lOng distance trip. I started driving and after about 60 miles or so my gas gauge started going down rapidly and then started going back u again. So I pulled over **** the car off an turn it back on after 5 minutes and still the same issue. So I pumped another 2 gallons and drove to my destination about 150 miles. The car ran with no problems. The car sat in the parking of the hotel Friday and Saturday all day and Sunday I started it to drive back and went to the has station on Sunday, I knew I'm low on fuel, I pumped about 5 gallons which is all its would take and drove off and about 140 miles later I pulled over to pump gas again as my gauge was still showing full. It took about 5 gallons and wouldn't take anymore at all and I tried and tried. So I started driving again and about 90 miles later I got close to home so I bought a bottle of techron and dropped it in the tank and pumped another 4 gallons and it wouldn't take anymore. I drove home and left the car over night and drove again today for about 100 miles and tried to pump gas at two different *** stations and the tank kept fighting me and wouldn't take more than a gallon. I tried pulling the nozel plastic neck up and still no go. So I'm going crazy trying to figure this crap out.

1. Do I have too much has and it's not taking anymore?
2. Is the vapor valve busted and that's why it's not taking gas? I would think of this was the case I would have been able to pump by pulling the nozle plastic up, but I couldn't!
3. Is there a way to check the fuel level with the gauge not reading right?

bobbyjo9

Geez Ash... I gotta say it sounds like your consumtion is normal with the mileage. Aside from the problems you had with the last fill up, I didnt really hear a problem. Normaly when a float on the sender sinks thats it and it will always read low. Whats the dash readout telling you for gallons?

VIPclk320

I was waiting and hoping for yOu to response, haha. The dash readout reads either full or empty nothing in between. But I'm not able to pump gas in the car because the nozel keeps on clicking and puping as if the tank is full. So my main concern right now is to see how much fuel I have in the tank, because if I have a lot then the pumping issue makes sense but if the tank is empty or low and I can't pump any gas then I'm assuming it is the fuel vapor valve. Is there a way to check the fuel level other than the gauge?

Just Is

I don't know that this will help, but my car requires me to fill it with the pump upside down most of the time. If I try to fill it the normal way it usually clicks and shuts off. I don't have the same gas gauge issues but this could temporarily help ya at least get fuel in

VIPclk320

Thanks for the response, I tried that as well and no go. I'm starting to think that my tank is full because even if the vapor purge valve was bad I could still pump gas by simply pulling the plastic neck of the nozel back and pumping the gas but it doesn't let me do that either.

bobbyjo9

Well you know you can get at least 250 miles from a tank. Tanks hold 16+ gallons. What worries me is assuming your tank was full before the last 100 mile drive, you only put in a gallon or so. I would have said you were down 3-4 gallons at that point. Without a guage reading, I dont see any other way to check the level other than a visual. I dont have a working knowledge on how our tanks work, but there must be a feed between them. I wonder if that may not be where your problem is. If your only working out of one tank, with only half capacity the guage will move twice as fast and filling will be off also. You could try "tapping" on both tanks and see if you get a different sound. Course you would have to run one empty first....

VIPclk320

spoke to a good friend of mine earlier that is a benz tech and he explained the problem. Basically because we have a saddle tank the driver side fuel level sender has apump that sucks the gas from the passenger side tank into the driverside tank. Now if that pump fails when you pump gas it only fills up the passenger side tank and the fuel cant travel to the other tank without the pump so the passenger side tank fillesup and you cant pump anymore gas and it shows as full even though one side is completly empty. So im replacing the fuel sender unit which comes with the suction pump and as an extra percwuction im going to change the other sides unit as well so i dont have to worry about it for a long time. Because of this matter my fuel gauge flauctuates between full and empty because its reading from one unit that its fuel and the other unit thats empty.

bobbyjo9

Ahhh good ta know... Dual tanks are always a hastle. Ive worked with a few different systems and Im always amazed how something so simple can be made so complicated! Least with the size of these tanks it shouldnt be too bad... maybe in the 70lb range if the tank is full. Id still try and drain the tank before you drop if you can though.

CurYousGee

Happened to be a few weeks back and i just keep putting in whatever the tank will take, then about a month later it started taking a full tank again.

VIPclk320

I found and fixed the problems, many thanks to my very good friend Art. the problem was that both my fuel sending units failed due to age. so i didnt know how much fuel i had in my tanks therfore i kept trying to pump fuel. What happens when you top off the fuel tank is that the fuel travels to the expansion tank (passenger side rear fender area) and then from there to the charcoal canister(driver side rear fender area) and once the carbon pelets in those gets wet and fuel gets inside the canisters the vapors have no way of escaping the fuel tank in order for the new fuel that you are pumping to come in(pressurised air bubble) therfore you can not put any new gas in. I was lucky that my over pumping pushed the fuel just to the expansion tank and didnt go further into the charcoal canister because that canister is very expensive. so i changed my fuel sending units and the expansion tank this morning and everything is good to go and brand new. in some mild cases when fuel gets into the charcoal canister it will evaporate with time but in more aggressive cases the lots of fuel gets in it and you have to take it out and empty it and let it sit for a few days to dry or in some cases that canister is just useless if the carbon pelets have soaked too much liquid(fuel) and you have to just buy a new one which is about $480. my problem was solved and everything is new and running perfect. the work was very straight forward and fast except me and my friend took a bath in Fuel.

NismoPower

Good Job Ash!!
Glad its fixed

CurYousGee

Hey Ash did you have to drop the tank to replace both sending units or are the accessible from the trunk or under the rear seats?

A1EK

...did the sender the units show signs of dirt or coating on the contacts?
My fuel reading has played up before just like yours showing that the car one minute has half a tank then it jumps to full and then empty etc. I found that this is common problem and the issue being that some cheap fuel has higher levels of sulper which coats the contacts in the sender units.
Both times this happened to me I managed to fix the problem with a bottle of fuel injection cleaner into the fuel tank as recomended by the forum, no need to replace the sender untis though.

VIPclk320

changing the sending units is very very easy. once the car is up on the lift there are two hatcjes on each side of the tank facing down, each hatch has 3 screws holding them in place, just remove those and the hatch and you will see the sending units. unplug the wires and turn the round metal holder counter clock wise til it comes out and the sending unit will drop down once thats removed. here are a few tips:

1. there is a tool to remove the round metal holder but what we did was just put to screws in 2 of the 4 holes and used a long extention to put inbetween and tuen it counter clock wise to open and clock wise to close

2. place a bucket under the sending unit as you are lossening the holder because gas will start coming out even without the sending unit compleetly out

3. when removing the units make sure to be very gentle because there are plastic parts and they dry over time being in gas and you dont want any piece to brake and create an obstruction for the fuel pump(and its hard to fish in there for a broken part

4. dont reuse the gas that came out of the tank

5. make sure to wear gloves and put your hands inside trash bags to make sure your arms are completly covered as you are removing the sending units. this is a must because your arms will be up and the gas will drian down your arm and go into your arm pits and side rib cage area. I know this sounds funny and corny but trust me i was burning for two days in the areas that i mentioned because so much gas came in to contact with me.

CurYousGee

Thank Ash, right now my car threw a P0450 code, tried clearing it but no dice. Will try the fuel cleaner A1EK suggested before i spring for the the more expensive option.

Cel was on and i thought it was the O2 sensor, so i changed all three sensor, and the last one i change over a year ago. Then when i went to clear the code there was the expected p0170 and p0173. So then i cleaned the MAF as well. But i got the suprise code p0450 that references the pressure sensor of the evap system in the fuel sending unit.

I had the same problem trying to fill up my car from empty a few times in the past so that might mean my pressire valve or charcoal canister is clogged, but that problem went away. But lately my fuel guage continues to fluctuate empty to full etc.

So between the fluctuating fuel level and the p0450 code for the evap fuel pressure senor, i think it might be the sending unit bc the sensor is built into the sending unit.

rorf

Poor quality fuel can cause havoc with the fuel gauge senders - Techron will usually fix it.

The other thing I learnt is to remove the ignition key when filling up, and my gauge has behaved for the last 90 000 kms.

VIPclk320

Hey George try using Techron from chevron, buy the smaller bottle and dump it in through the gas tank when emmpty and full up all te way and start driving the car hard. I have to say though chances of that working is very slim more than likely have to change the fuel sending unitis how ever it's worth a try.

CurYousGee

Cool i'll give that a try, i usually fill the gas with chevron 91 octane, and i never top off, so other than age, i cant think of any reason why it would fail, so sound like i will have to replace it soon

CurYousGee

Hey Ash or Marcus, trying to order the fuel sending units , from my research there are 2 , left and right, but when i punch in the year make and model for my 2000 clk430, it comes back with only the right sending unit only. When i change the year to 1999 it has both units. Was there an update? Or is the database autohausAZ incorrect? Pelican parts has both listed as a cross reference, so i am thinking there is two and autohausaz database is wrong?

And lastly, Ash did you use the mb units or the aftermarket vdo units?

VIPclk320

honestly not sure about that but as far as I know all he models use the same unit all across the board (320,430,55)

MarcusF

Sorry, I'm a long ways from my WIS/EPC. I'll have access mid-week

CurYousGee

Thanks Ash and Marcus, let me know what you find out later this week, a few months back i discovered that different year w208 took different O2 sensor when i accidentally ordered one for a 2001 instead of a 2000, since then i have always check plus and minus one year to be sure and was surprised to see ths difference thru the autohausAZ database.

VIPclk320

o2 sensors yes but I can tell you from experience I changed my fuel sending units because one went bad so I decided to change both of them about 6 months before I did the transplant and when I did the transplant the new wiring harness plugged right into them and they work just fine.

CurYousGee

Cool thats great to hear, ill be ordering both side soon, did you go with oem or aftermarket? Did they make any improvements from the original to make it last longer?

VIPclk320

I use only oem.