Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Tech Help

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 05-14-2011, 08:44 PM
86560SEL's Avatar
Registered User
 
Join Date: Jan 2003
Location: east Tennessee (southeast USA)
Posts: 3,015
Brand new fuel sending unit, fuel gauge still inaccurate....

Finally took moms car in to have the fuel gauge repaired. When I bought the car 4 years ago it was on the fritz and even ran out of gas once right after purchase before it got down to "R". Over the years, just kept filling it up, but finally took it in. She took it and he put it on the lift and told her the fuel pump was leaking. I dont know, I had never smelled any gas or seen any drips. Anyway, she called dad and he gave the green light to replace it. To fix the fuel gauge (he said it needed a new sending unit) and fuel pump was going to be $600. They said do it. Went and picked it up next day and the fuel gauge still erratic. Said 1/2 tank when she left... less than a mile down the road it shot up to 1/1. Then back down to 1/4, etc. He called, said to bring it back, which we did the other day. He said that its possible that the new unit is defective, he had ordered another and to bring it back next week.

What are the chances for a brand new Bosch sending unit be defective? If its not the sending unit, what else would cause the fuel gauge to read 1/2 one minute, then full the next, then back down to 1/2 two miles later, then back to full a mile later? For $600.00, you would like a working and accurate fuel gauge indicator since thats why you took it in to begin with. So basically $600. later, a new fuel pump, but gauge still broken.

Thanks.

(Btw, its a gasoline gen 2 W126).

Reply With Quote
  #2  
Old 05-15-2011, 10:44 PM
86560SEL's Avatar
Registered User
 
Join Date: Jan 2003
Location: east Tennessee (southeast USA)
Posts: 3,015
I thought erratic fuel gauges were common on the W126's. Guess not. I thought I was lucky with my '85 W126s working gauge.

Interesting.
Reply With Quote
  #3  
Old 05-18-2011, 06:23 PM
86560SEL's Avatar
Registered User
 
Join Date: Jan 2003
Location: east Tennessee (southeast USA)
Posts: 3,015
Oh well. Car was taken back to shop, another new sending unit put in and 1/2 way home it went from 1/2 tank, then it shot up to reading full tank and when mom pulled in it was down on "R". So basically $600.00 later and still the fuel gauge is broken (inaccurate).

She called and he said it could be where a mouse or something chewed a wire under the seat and he would check it, but if he had to remove the tank or some kind of panel, it would be another $300-400. I am about to tell her to just junk it out. This is crazy. She is getting a new car later this summer, but we were hoping to get this one to suffice for a few more months.

Oh well.
Reply With Quote
  #4  
Old 05-18-2011, 08:26 PM
Registered User
 
Join Date: Dec 2007
Location: NorCal
Posts: 1,332
It's more likely that the actual physical gas gauge is defective. Also, sounds like this mechanic is a crook.
__________________
http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...
Reply With Quote
  #5  
Old 05-18-2011, 11:20 PM
86560SEL's Avatar
Registered User
 
Join Date: Jan 2003
Location: east Tennessee (southeast USA)
Posts: 3,015
Quote:
Originally Posted by JohnM. View Post
It's more likely that the actual physical gas gauge is defective. Also, sounds like this mechanic is a crook.
Sounds horrible. I hope not, after spending $602.00, not really looking to put more into it. Sad part is this is the only German car specialist in our city. There are more in the next city over, about 25-30 miles. Should have went elsewhere, but we had heard good things about this place. Oh well. He was supposed to have checked it to see what the problem was first. Possible that the sending unit and gauge itself are defective? If the gauge itself is bad, I guess all one could really do is swap out the cluster?

Does anyone know where the wire runs that goes to the sending unit? I have not had the seat out, but I would think the wire would be visible. Im confused. My mom is worried to death about it. We have been filling the car up every few trips out, but its getting old. I dont want her running out of gas.
Reply With Quote
  #6  
Old 05-18-2011, 11:22 PM
Registered User
 
Join Date: Dec 2007
Location: NorCal
Posts: 1,332
I doubt the wire is visible. Probably in a loom. I think he was talking out of his ass. A W126 isn't an old Volkswagen.

Gas gauge assembly / oil pressure / temp can be separated from the other gauges. A good used one should be under $25. I might even have one that you can have for the cost of shipping.
__________________
http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...
Reply With Quote
  #7  
Old 06-03-2011, 06:42 PM
Registered User
 
Join Date: Nov 2004
Posts: 121
Talking fuel gauge flacky

Hello,

had a similar issue.

make sure you check the ground connections

the mercedes system is based on resistance between the gauge and fuel sender unit. if the ground is not good[additonal resistance in the ckt] it will not work right.
w124 has the gound for the sender left hand side looking from the back. have to rempove the covers in the trunk. remove the brown wires [on w124 all the brown are grd]and clean well, may have to resolder?

fixed mine after a new senders unit was purchsed and didnt fix the problem?

gavinbr
Reply With Quote
  #8  
Old 06-04-2011, 08:09 AM
Registered User
 
Join Date: Dec 1999
Location: Utrecht, the Netherlands
Posts: 415
The sender has two resistance wires and a float with contacts that slide over the wires.
With the float in top position the resistance is minimal, at the bottom position the resistance is maximal.


It is not possible that the resistance is lower than the minimum for a given float height. Higher resistance is possible if the wires are corroded. So malfunctioning of the sender will result in a lower fuel reading, never a higher. The same for the ground (located on the left rear wheel well), bad ground result in a lower fuel reading.


In addition there is a low fuel warning light..


In the instrument cluster the ground and power are shared with the coolant temperature gauge and the oil pressure gauge, are these behaving properly?


Ground is also shared with the high bean indicator light, you can check the ground by switching to high beam an see if the fuel gauge reading changes.

Rob
Reply With Quote
  #9  
Old 06-04-2011, 09:00 AM
Cal Learner's Avatar
Registered User
 
Join Date: Aug 2006
Location: Marysville, CA
Posts: 781
Rob and gavinbr: Interesting and useful information.
__________________
1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't
Reply With Quote
  #10  
Old 06-05-2011, 07:27 PM
86560SEL's Avatar
Registered User
 
Join Date: Jan 2003
Location: east Tennessee (southeast USA)
Posts: 3,015
Thanks. We are not going to worry about it. We are really not experts in this area and which is why we paid the mechanic (supposedly a Mercedes tech) $600 to fix it. We are not even going to bother checking this and that for ourselves.

Now he (the so called Mercedes mechanic) wants another $300 to work on it again. Its not worth it, I only paid $2000 for the entire car 3 years ago. We will just fill it up with fuel every 2 or 3 days like we have been doing for the past 2 years. Very agitating, especially once you have paid a mechanic alot of money to repair it. He said maybe a mouse has chewed up a wire and he would have to search and charge another $300.

Good and reliable mechanics (especially for German cars) are very difficult to find around here.

Hopefully dads retirement will come in very soon and she can get that brand new Buick she wants.

ROB, yeah all of the other gauges there (oil and temperature) are working perfectly. The low fuel light also comes on, but not before it runs out of gas.

Last edited by 86560SEL; 06-05-2011 at 07:39 PM.
Reply With Quote
  #11  
Old 06-05-2011, 07:39 PM
engatwork's Avatar
Registered User
 
Join Date: May 2000
Location: Soperton, Ga. USA
Posts: 13,646
Quote:
if he had to remove the tank
find another mechanic.

You've got a bad wire/connection somewhere.
__________________
Jim
Reply With Quote
  #12  
Old 06-05-2011, 07:44 PM
86560SEL's Avatar
Registered User
 
Join Date: Jan 2003
Location: east Tennessee (southeast USA)
Posts: 3,015
Quote:
Originally Posted by engatwork View Post
find another mechanic.

You've got a bad wire/connection somewhere.
Yeah, I wish we never had of even used him, but he is about the only one in town that specializes (or so called) in German cars. We should have took it to Benz Doctors 20 miles from here instead, but we didnt, that was our mistake - we only went to this other one because he was closer, what a joke.

Its a shame now to put even more $ into it, but I guess we will. Mom is getting a brand new car in a couple of months, but I would like to keep this one as an extra car to beat around in. Its still a really nice car. I will tell you though I will NEVER recommend anyone to take their car to that mechanic again.
Reply With Quote
  #13  
Old 06-06-2011, 06:21 AM
Registered User
 
Join Date: Dec 1999
Location: Utrecht, the Netherlands
Posts: 415
If you send me an email (with you email address) I can send some (small) docs about testing the fuel gauge.

If you print these and take them to you mechanic it may help him to find the problem.

Rob
Reply With Quote
  #14  
Old 06-07-2011, 09:27 AM
Registered User
 
Join Date: Aug 2002
Location: Southeastern PA
Posts: 3,077
86560SEL, tell the mechanic you want the old fuel pump. Chances are it was fine and didn't need to be replaced. Though it is important to replace the fuel filter every 60,000 miles.

__________________
Fred Hoelzle
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 04:46 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2024 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page