W126 Fuel Gauge Poll (working or not)

[LandYaghtLover]

Wondering about those that may or may not have issues with the fuel gauge fluctuating or not reading below a certain level. I am curios because I recently removed my twin 12" subs and pulled the fuse on the sub amp to transport some tires rims. Since then, my fuel gauge has been MUCH more accurate. Only slight fluctuations. And for the first pretty much ever, the gauge is reading below a quarter tank. It usually never read below half a tank, even when on reserve. So in my case at least, I think the subs or bad amp wiring are the issue.

[Hit Man X]

They both work poorly in my second gen cars. No aftermarket stuff in them. I even replaced the fuel sender in one, waste of money. Now I just fuel up off mileage.

Both my first gen work decent. They jump around a bit, yet are the OE senders so I am pretty sure they are worn out. My SD has an aftermarket radio, the SDL does not.

[JohnM.]

Something is wired wrong if your fuel gauge is affected by your stereo, it could have just been a coincidence too. Never had a problem with fuel gauge accuracy (W124 though), aftermarket stereo or not.

[LandYaghtLover]

Originally Posted by JohnM.

Something is wired wrong if your fuel gauge is affected by your stereo, it could have just been a coincidence too. Never had a problem with fuel gauge accuracy (W124 though), aftermarket stereo or not.

I am thinking the same, but before I remove things I am wondering what other are experiencing.

I think in my case I picked a bad ground location.

On another not, I had replaced the resistors on the fuel gauge. And just recently I re-soldered the speedo board when I realized the fuel reading goes through it. Both job increased the reliability in that: Over a half tank it reads fairly well and the needle no longer jumps all over.

So now I need to tinker more with it out.

Question: When the reserve light comes on, which is how I fill-up, where should the needle be? I would think at empty (last line on left).

[LandYaghtLover]

I cant not find the thread, but I thought there was one for best routing of power wires, etc. An over-all post about installing a system in a W126. Anyone have that thread?

[Stretch]

How much power does your sound system soak up? Did you upgrade the alternator?

[LandYaghtLover]

Yup. Alternator is a 110amp. The system has a 650 watt for the subs and a 600 watt for the 4-chanel. The system is VERY old. Going on 10 years.

Fuel gauge is still working very well with the subs out of the trunk. Every so slight fluctuations when very near empty. I think I will put the subs back in tonight and see what happens. If there is a change, I will start moving grounds or look closer at the wiring (again).

[compu_85]

Mine is perfect. When I get the car out here I will be installing an Infiniti Basslink.

-J

[86560SEL]

Fuel gauge in my old '85 380SE I owned in 2004 worked perfect. Bought my '88 300SEL in October of 2008 and its been flaky since day 1. Gave car to mom last summer, she paid a "Mercedes shop" $300 to put in a new sending unit (he said that was the issue), put a new one on and still dont work right... wanted to charge her $300 more, so we said forget it.

It will be on 1/2 tank, then its back on full, then back on 3/4, then back on full, then 1/2, blah blah blah.

[LandYaghtLover]

Originally Posted by 86560SEL

Fuel gauge in my old '85 380SE I owned in 2004 worked perfect. Bought my '88 300SEL in October of 2008 and its been flaky since day 1. Gave car to mom last summer, she paid a "Mercedes shop" $300 to put in a new sending unit (he said that was the issue), put a new one on and still dont work right... wanted to charge her $300 more, so we said forget it.

It will be on 1/2 tank, then its back on full, then back on 3/4, then back on full, then 1/2, blah blah blah.

I think, for the most part, replacing the three resistors on the fuel gauge pod helps along with re-soldering the speedo board. Mine was all over also, but after that work is was very stable. Now that I took out the subs, it reads more accurately, but its not as stable near low. I think its because I adjusted the pot on the fuel gauge pod and it may be reading below empty, if you know what I mean. Basically out of range.

I did not have a chance to put the subs back in. I keep forgetting to grab the box from work.

[grob6000]

I have the same problem (intermittently jumpy when under 1/2 full) and I've noticed if I give my dashboard a #3 BST (British Standard Thump, "fairly solid") the fuel gauge will jump around, and sometimes settle down. It looks very much like a wobble-fault (where some electrical connection is loose / flaky), especially considering the fuel sensor signal is likely to be much higher impedance than the speedo / etc.

I plan to take the instrument panel out, check the solder joints around the fuel gauge, and clean up the ground connector, then see what happens.

On another note, resistors are unlikely to perish over time like capacitors - if they seem to be troublesome, it's often the solder joints - worth going over them if you've got it out and on the workbench anyway. Fixed an apparently dead cruise control unit that way a while ago...

[bricktron]

i would reflow the solder on any and all joints you can get to. it's very common on old circuitboards that a part or wire comes partially loose and that remelting the solder on its lead will remake the proper connection.

[LandYaghtLover]

While resistors can last pretty much forever, they can not if they ones used are not rated for the job. I have plenty of electronics that have failed due to bad resistors. Installing one that can handle more load always solves the issue.

I think in this case I replaced mine after reading much into this. It was found they are not sufficient.