'73 220D Fuel Gauge

[catfish]

my rotten fuel guage quit on me a few days ago. does the system use an electric sending unit or a bobber in the tank? i looked under the mat in the back, and it looks like there is a 5" plastic cap to access the tank from the trunk? maybe something in the cluster? i have been meaning to pull it out to get to the clock...

of all the things i WANT to work, this is one! along with the wipers, brakes, and brake lights. i can do without everything else! i love old cars!

thanks guys. cody

[W.L.SOON]

Hi guys!Yeah,I've been wanting to find out how do one gain access to the fuel level sender unit? Mine,a 1972' 230,has a few of these large round metal covers in the boot/trunk floor;can't figure out which one to pry open;hopefully I'll get to know the exact one as they're a bit rusty!

Hopefully,you guys could help me out here....and I hope Cody won't mind me bumping in here....
Well,thanks again.BYE for now and have a BLESSED NEW YEAR!!! :) :) :)

[pch2021]

silly children. here are the steps (:


NUMBER 1: lift up your trunk mat. at the center you will find a tan plastic cap. Lift it up and there is thew three prong plug.

number two, check yuor fuses. catsfish...your fuse box is in the left hand fender, secured by two hand screws. the fuel gauge is on number one, along with a bunch of other items.

if the fuel gauge is stuck,it may be due to dirt. it is in by 6 8 mm nuts. the tank may have to be lowered a bit slightly to retrieve it, but usually not.

the plug is simple. three wires. test for power coming to it. if it is receiving power with the ignition on, rewmove the sending unit. the lead wire inside might be broken, and is difficult to fix. ANy era fuel gauge will work from a 115,114 or 108. it mneed not be from a diesel. It has a plunger inside[not a bober, like the older volvos] that is inside a hollow canister.

a more critical issue is failure of the fuel gauge itself. The only way to test this is is to have a wiring diagram. If you unplug the cliuster, i beleive there are 17 pins in the plug. I AM NOT SURE but number 3 might be the fuel gauge. they changed them three times, so far.

also, check the plug itself. itneed sot be secure. Mkae sure the car has atleasdt half a tank of fuel in it. also, to test the reserve light, place the new sending unit, empty, on the ground, hooked up with the ignition on. A small, yellow light on the cluster should illuminate.

[MBman]

if the wires are broken they can be repaired but it takes a steady hand and nichrome wire, I just did it on my 71 with good results

[pch2021]

hehe...i did it too! It worked for about a year.

[catfish]

upon checking the fuse, i noticed that is was OK! ha! i may just have a chance at this mechanical stuff! anyway, the ground wire pulled from it's connector (i stuff computers into the trunk all day and may have stuffed to hard). i replaced it with a similar wire of my own conjuration and it is working again.
i pulled the sender float thingy and played around until the triangle RES light lit up to diagnose.

merci beaucoup

[dcashour]

My fuel guage is working about 25% of the time. Sometimes it sits on one spot, and I think it's fairly accurate. Most of the time the fuel guage needle bounces back and forth like a possessed demon--it makes me nervous just looking at it!

Fuse is good. do I want to pry off that cap in the trunk, then remove the 6 8mm nuts? Will the unit then slide up and out, or do I need to unfasten it in some way? Once out, what do I want to look for?

I'm wondering that since this car sat idle for a few years, do I want to drop the fuel tank anyway and clean it in case there are bad critters in there? Is dropping the tank a big PIA and/or unneccessary?

[Odrec]

I had this on a W124, it all ended up being a rusted tip on the ground wire. But better listen to Mr. PCH.

[Don350SDL]

. Most of the time the fuel guage needle bounces back and forth like a possessed demon
Often a sensor issue. Take it out and make it slide up and down it's track (it's inside a metal tube, it'll be obvious when you have it out) a few hundred times to clean it, and it'll be fine (for a while).

Absolute diagnosis method is to simulate the fuel sensor with a resistor (you have to look up the values, but my '91 350SDL uses 3 ohms for full and 86 ohms for empty) and see if the gauge holds steady. Need to try a few values. If steady, the sensor is the problem. If jumpy, wiring or gauge is the problem.

Don

[MBman]

My fuel guage is working about 25% of the time. Sometimes it sits on one spot, and I think it's fairly accurate. Most of the time the fuel guage needle bounces back and forth like a possessed demon--it makes me nervous just looking at it!

Fuse is good. do I want to pry off that cap in the trunk, then remove the 6 8mm nuts? Will the unit then slide up and out, or do I need to unfasten it in some way? Once out, what do I want to look for?

I'm wondering that since this car sat idle for a few years, do I want to drop the fuel tank anyway and clean it in case there are bad critters in there? Is dropping the tank a big PIA and/or unneccessary?


Take it out when fuel is low , let it drain before you fully remove it. When you take it apart it will be full on gunk, and the wires will be crusted, be very careful when you clean, you don't want to break those wires.

[dcashour]

Here's the fuel sending unit. I cleaned the contacts on top, and I can hear/feel the thing sliding inside. Is there anything else I can do with this? It doesn't look like it will come apart any more than it is. I cleaned the metal posts for the electrical connection. Suggestions?

Forrest crapped out on me at 5:30 this morning. I suspected he was out of fuel. I had a 1.5 gallon of canola oil in the trunk, so I poured that in the tank, primed the pump and he started right up. I found a filling station and added 2 gallons of diesel, so there should only be about 3 or 4 gallons in there. But when I look in the tank it appears to be almost half full. With a capacity of 17 gal, something doesn't look right. Maybe some gunk got on the tank strainer and clogged it? When the car pooped out, the fuel guage read EMPTY, but that doesn't mean anything since it's not been working properly. Any thoughts?

Thanks.

[MBman]

Dave
Have you changed the in tank filter??
I would suggest you drop the fuel stainer/filter in the tank (very messy job) but it is a necessary step if you have not done it. Replace it with a new one, although the old one can be reused after cleaning.
I would then take compressed air and blow out the lines FROM THE ENGINE BACK to the tank.
The set up for these tanks has the fuel inlet and outlet in the bottom of the tank that easily cruds over and can restrick flow.
As far as the gauge, there is a small nut on the bottom, carefully remove and then pull unit apart, be very very careful of the nichrome line. It will be evident what needs to be cleaned or repaired. I also have a rebuit unit if you cannnot get yours to function

[dcashour]

I didn't take the sending unit apart, but I did inject some parts cleaner into it and shook it about a million times as Don suggested. I saw that tiny nut that you referred to. Lots of black goo camp out of the tiny holes, so it was filthy. I put the unit back in, and now the orange triangle indicating low fuel is lit. I think I've got about a third of a tank full. I think there's still crud in the sending unit and probably lots more in the tank. Something probably blocked the IN line, and when I dumped in the veggie oil, it may have moved the crud. Actually, that veggie oil will probably scour the tank and clean it real well. I should expect more crud to break loose and give me headaches. I'll have a look at the tank strainer and see what's up.


Do I need to remove the whole tank to get to the strainer? I'm assuming I should first remove the IN line, and let the tank drain first? Never did this before. Will also blow lines out as you suggested.

thanks

[MBman]

No tank filter is on the bottom center. It is a large allen wrench set up, if you do not have a wrench this big toy can often fabricate ine from a nut or other driver. I actually used a large vice grip. Probably not the best solution but it worked. The replacement filter was an aluminum set up dso I had to becareful with the grips
There is a gasket with this set up so have your parts ready
When I did mine I thought I had about a gallon or so of fuel, ended up about 5 gallons of stinky old stuff, what a mess.
You can drain a lot but taking off the in and out lines at the tank. One note of caution is that the exit line( i think, it is one of them) is a special little hose that has two diameters (in/out) I had to order one as mine got trashed when I removed it.

[dcashour]

Attached are pictures of fuel sending unit. The larger copper wire is severed. I believe there are two thinner wires (previously referred to as nichrome in earlier reply to this thread). It looks like they attach at the top at bottom by means of solder connections. It also looks like they ride on the outside of the float, in between two metal connectors with which they would constantly maintain contact. The larger copper wire, it seems, rides inside one of the other grooves in the float. The larger wire seems to serve the purpose of either making or interrupting the circuit when the float makes contact with the bottom, hence triggering the low fuel indicator in the instrument cluster. Are the thinner wires in place to indicate the fuel level? How does this happen?

MBman said he used nichrome wire. I thought nichrome was used for heaters and things like that. If so, would you want these wires to get hot inside the fuel tank? :eek:

Anyway, if I have correctly described where these wires go, it seems to me that I could repair this unit without too much difficulty. Does anyone know where I could come by nickel chromium wire of the proper guage?

[MBman]

the thinner wire is one contiuous piece, from top, aound bottom to top again,
the float rides up and down on these wires and by means of the position on the wires it either increases or decreases resistance and gives the guage a reading, all the way down and the circuit closes and the light (low fuel ) comes on.
What you need is 40 AWG Ni Chrome wire for proper resistance. I think I have some , if you send me a self stamped envelop I will send you a length

[W.L.SOON]

Hi guys! One end of the nichrome(actually I don't know what type of wire it is,but you guys say so.....)is attached to the G(Gauge) terminal.From there it goes down,make a loop and comes back up to the copper piece,which is attached to the Earth/Ground terminal.Now,study the copper piece thingy:you'll see that the larger COPPER wire is attached to it too,the wire goes down to the bottom,to one of the pointy contact.Now,how about the other pointy contact?Well,it's connected to the centre metal pole,which goes up to the TOP metal plate(yeah,the greyish piece above the copper piece).The metal plate is attached to the W(Warning lamp:Low fuel)terminal.The other terminals/copper piece thingy is INSULATED from the metal base.

Since the nichrome wire has high resistance,the bobbing unit(float)alters the value by moving up/down:as the contacts on the float are BRIDGING the 'two' wires together:thus resistance is lowest(approx. 6 ohms)when float at the highest(Full tank) and highest(approx. 66-67 ohms)when float hits bottom(Empty tank).

You see the circular metal plate at the bottom of the float?When the float bottoms out,it'll connect the two pointy contacts,thus this'll ground the W circuit and light up the warning lamp.

Dave,you said that (ONLY)your copper wire is broken.It may be touching the centre pole or the topmost metal plate,and this'll light the lamp up.Since the copper wire only serves to complete the earth circuit(for the W circuit),any copper wire will do,as you do not need to vary the resistance value,as in the long strand of nichrome wire where the float rides.

Get a new piece of copper wire,taut it up between the two contacts and solder it on.It mustn't be too thick where it'll interfere with the sliding float(keep it in the float groove),and preferably not to touch the outer alloy casing(tho' it is insulated from the circuit,but you know.....)

Nichrome wire will perhaps heat up when we pass large amount of electricity thro' it(hey,Physics isn't my favourite subject,to say the least :cool: ),but here,the amount is minimal:it is AFTER the gauge,you see.

Well,all the best to you.BYE for now and GOD BLESS you folks!!! :) :) :)

[MBman]

actually the thin nichrome wire will have a resistance of less than 1 ohm. If you use higher resistance wire you will not get the step gradient needed to tell the guage what to do

[dcashour]

Thanks W.L. and Ron. I've now got the jist of it, and I can see how the proper guage nichrome wire is critical. I don't think I'll have any trouble getting it set up properly once I get the wire from Ron.

[dcashour]

Okay, MBMan sent me the NiChrome wire and some copper wire, and everything seemed to go well with soldering and properly connecting the wires. I tested the resistance, and I got 5.1 ohms at the top position and 49.8 at the bottom, which I think seems normal. So I put everything back together, turn the key, and the stinking fuel gauge still doesn't read. :mad: It's stuck in the "R" zone. When I turn the key, the needle moves slightly to the left, maybe 1/16", as if there's some sort of reversed polarity issue. :confused:

Is it the gauge? If so, does anyone know how to test it? Earlier in this thread or somewhere, Pierre talked about the 17-pin connector in the instrument cluster, but this is meaningless to me. Any ideas will be appreciated.

MBman, many thanks for the NiChrome wire and the instructions.

[MBman]

Dave,
I believe when the float hits the bottom you should get continuity (closed )and not an ohm reading i could be wrong but I think that is what gets the low fuel light to come on.
Also if your instrument cluster is not grounded properly your gauges will not work. Try to manulaly ground it and see if the gauge works.
Is your connector coroded? You could always connect a potentiometer to the sender and see if it can rise and fall with movement of the float

Also make sure the little copper arms are properly set against the nichrome wire , the large copper wire acts as a guide, no copper arms there

also check continuity on your lines, sometimes the solder may look good but actually is not providing good connection
Good Luck

[dcashour]

It's working intermittently now. After the car is running, the gauge bounces around a little then settles down. I filled the fuel tank, and it registered full. Now it's down a little, so it may be okay. I'll need to run the tank down and see what it does.

The instrument cluster is fine--everything works. I took the fuel sending unit apart again to double check the wires, and they're okay. The connector at the sending unit is clean and working. I think I'll need to test continuity on the wire leading from the sending unit to the gauge, and check the connection on the gauge. When the sending unit was out of the tank, I could slide the float up and down, and could see the guage registering, though I couldn't get the low fuel indicator light to come on. As you've suggested, I'll also check the solder connections on the connector and everywhere else where there could be a connection. It's very quirky.

I removed the tank strainer, and it had some gunk on it, so I removed the tank and cleaned it. It was surprisingly very clean. I think the vegetable oil was doing it's job. The pre fuel filter and main fuel filter were black! I changed both, and now I have a clean fuel system.

Thanks for all the help so far.

[MBman]

great, mine bounces around a bit as well, if you are using veggie oil, I would think the viscosity may have something to do with it, but not sure.

[MBman]

Dave,
Hows it going, catching up on some of my posts, raining here and allows the much needed time. Get the gage working?
I really should be doing some bondo! :D

[dcashour]

Gauge seems to be fairly accurate, but sometimes it doesn't work at all. There must be a short or broken connection somewhere. Just no time to look into it lately. I'll need some rainy days to prompt me to get after it.