My 404 fuel gauge is pegged full all the time??? - Mercedes-Benz Forum
Reply
 
LinkBack Thread Tools Display Modes
#1 (permalink) Old 05-05-2013, 05:50 AM
BenzWorld Junior Member
 
yyeettii's Avatar
 
Date registered: Apr 2013
Vehicle: 1972 MOG 404 / 1963 VOLVO C202 LAPLANDER
Location: Rio Rancho NM
Posts: 22
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
(Thread Starter)
My 404 fuel gauge is pegged full all the time???

Cant figure out whats wrong with it. You turn on the key, and it reads full. I pulled both leads off the tank and it reads the same until I turn off the key. Traced the wiring for a pinch ground, but nothing. I can however pull off one of the 3 wires at the gauge and it will go to empty. What gives???
yyeettii is offline  
Sponsored Links
Advertisement
 
#2 (permalink) Old 05-05-2013, 06:36 AM
BenzWorld Elite
 
DokaTD's Avatar
 
Date registered: Sep 2005
Vehicle: 85' U1300L Holset Turbo VA A/C, 66' Propane 404.1 rock mog, G500
Location: Unknown
Posts: 4,364
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 22 Post(s)
Did the gauge work before? If not, are you positive your reading the gauge right?

FOR SALE: 1985 U1300L 200HP $50,000
FOR SALE: 1969 404.1 crawler mog $25,000

DokaTD is offline  
#3 (permalink) Old 05-05-2013, 06:57 AM
BenzWorld Member
 
schroeck's Avatar
 
Date registered: Jan 2011
Vehicle: 1978 406 w/ Eller hardtop
Location: Cincinnati, OH
Posts: 84
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I have the same problem on my 406.

I eliminated the gauge as cause by putting resistors in place of the sender. A 100 ohm resistor should yield a reading of 1/2 full on the gauge,

If I does, then you have eliminated the gauge and wiring harness.

That leaves the sending unit and its connections as suspects. That's where I am now.

Best of luck. I'll report more as I learn it.

Schroeck


Sent from AutoGuide.com Free App
schroeck is offline  
#4 (permalink) Old 05-05-2013, 07:33 AM
BenzWorld Elite
 
Date registered: Nov 2004
Vehicle: '88 U-1300L, '70 406, '78 406, '78 416 project, '82 406, '57 404, '65 404, '70 404, '68 Haflinger.
Location: Greenback, TN
Posts: 1,656
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Ya'all are on the right track. The full-tank gauge reading is caused by an open circuit at or to the sender. The sender is about 200 Ohms so may be checked with an Ohm meter. Remember to compensate for however much gas is in it. Any reading up to 200 Ohms is probably good.

One of the wires at the sender has to be to ground. If ground is lost the gauge goes high. Clean up all the screws that hold the sender into the tank (to ground the sender to the tank) and also verify the ground wire is clean on it's screw.

If the gauge has never worked then it's possible the two wires got switched sometime. Same results, full reading. I had a 404 wired that way once. The brown wire should be the ground if I remember right.

After all that, if the gauge still does not work then put a variable wire-wound pot across the two sender wires. The test with the 100 Ohms is a great test but it's kinda nice to see the gauge move from full to empty to verify the dash meter is ok.

Another hint. The sender can be taken apart and the resistive element repaired and/or cleaned. Have to drill out some rivets. If the gauge is working sometimes but jumps to full as the fuel sloshes, there is a dirty spot on the resistive element.

Bob
hammogger is offline  
#5 (permalink) Old 05-05-2013, 11:41 AM
BenzWorld Junior Member
 
yyeettii's Avatar
 
Date registered: Apr 2013
Vehicle: 1972 MOG 404 / 1963 VOLVO C202 LAPLANDER
Location: Rio Rancho NM
Posts: 22
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
(Thread Starter)
Yah, I pulled both wires off the sender and its still full unless I turn off the ignition. I have cleaned all the connections. I will ohm it out. Thanks for the info.
yyeettii is offline  
#6 (permalink) Old 05-14-2013, 08:30 PM
BenzWorld Member
 
schroeck's Avatar
 
Date registered: Jan 2011
Vehicle: 1978 406 w/ Eller hardtop
Location: Cincinnati, OH
Posts: 84
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Fixed my fuel gauge-and here's how

After two years of checking my fuel level by looking in the tank...and by the even more definitive method I call "running out of fuel", I have made the fuel gauge work.

After carefully opening up the sending unit to expose the wirewound potentiometer inside, I re-soldered the connection of the super-thin potentiometer wire to the blue wire in photo.

Then I soldered the other end of the blue wire to the terminal at the top of the sending unit.

Last, I cleaned the contact surfaces of the potentiometer and the contact on the float arm with a spray electronics cleaner, and carefully re-assembled the sending unit.

Luckily for me, the one I have was held together by bent metal tabs--but yours may have rivets like hammogger mentioned.

Now, it reads 7/8 when it is COMPLETELY full, and reads 1/8 when it is 1/4 full. A bit pessimistic, but it totally works for me.

It might be possible to get more accuracy with cleaner terminals, or with some sort of tuning pot added to the system...but I don't think I'll bother.

Schroeck
Attached Images
     
schroeck is offline  
#7 (permalink) Old 05-14-2013, 09:25 PM
BenzWorld Junior Member
 
Mog70's Avatar
 
Date registered: Nov 2012
Vehicle: 1970 Unimog 406 was VF3 Snowcutter
Location: Ventura County
Posts: 39
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Funny I got up the gumption to check mine out this weekend too unfortunately I wasn't so lucky/persistant. The ultra fine wire was broken in two places on mine right where the wiper goes which explains why mine read full then started working at half tank. Since the phenolic/fiber insulator is swaged in there and I didn't have any ultra fine wire around I honestly gave up, and just ordered a new one. See pics for what can go wrong.
Attached Thumbnails
Click image for larger version

Name:	tn_IMG_4670.jpg
Views:	37
Size:	57.9 KB
ID:	515228   Click image for larger version

Name:	tn_IMG_4671.jpg
Views:	46
Size:	43.4 KB
ID:	515229   Click image for larger version

Name:	tn_IMG_4672.jpg
Views:	44
Size:	41.0 KB
ID:	515230   Click image for larger version

Name:	tn_IMG_4673.jpg
Views:	35
Size:	43.2 KB
ID:	515231   Click image for larger version

Name:	tn_IMG_4674.jpg
Views:	41
Size:	88.7 KB
ID:	515232  

Click image for larger version

Name:	tn_IMG_4675.jpg
Views:	40
Size:	62.1 KB
ID:	515233   Click image for larger version

Name:	tn_IMG_4676.jpg
Views:	44
Size:	80.2 KB
ID:	515234   Click image for larger version

Name:	tn_IMG_4677.jpg
Views:	63
Size:	43.1 KB
ID:	515235   Click image for larger version

Name:	tn_IMG_4679.jpg
Views:	50
Size:	80.7 KB
ID:	515236   Click image for larger version

Name:	tn_IMG_4678.jpg
Views:	43
Size:	33.1 KB
ID:	515237  

Mog70 is offline  
#8 (permalink) Old 05-14-2013, 09:26 PM
BenzWorld Junior Member
 
Mog70's Avatar
 
Date registered: Nov 2012
Vehicle: 1970 Unimog 406 was VF3 Snowcutter
Location: Ventura County
Posts: 39
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Couple more
Attached Thumbnails
Click image for larger version

Name:	tn_IMG_4680.jpg
Views:	60
Size:	72.4 KB
ID:	515238   Click image for larger version

Name:	tn_IMG_4681.jpg
Views:	64
Size:	72.3 KB
ID:	515239  
Mog70 is offline  
#9 (permalink) Old 05-15-2013, 05:46 PM
BenzWorld Elite
 
Date registered: Nov 2004
Vehicle: '88 U-1300L, '70 406, '78 406, '78 416 project, '82 406, '57 404, '65 404, '70 404, '68 Haflinger.
Location: Greenback, TN
Posts: 1,656
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Excellent photo documentation, thanks!

Bob

PS, the ni-chrome wire can be soldered with some types of 'exotic' solder. I have some stuff called Eutectic Rod that adheres to the wire. Looks like that latter example was beyond hope.
hammogger is offline  
#10 (permalink) Old 05-15-2013, 09:37 PM
BenzWorld Junior Member
 
yyeettii's Avatar
 
Date registered: Apr 2013
Vehicle: 1972 MOG 404 / 1963 VOLVO C202 LAPLANDER
Location: Rio Rancho NM
Posts: 22
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
(Thread Starter)
Im taking mine apart!
yyeettii is offline  
Reply

  Mercedes-Benz Forum > Mercedes-Benz Vans/Trucks/SUV/Others > Unimog


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



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 Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome