I keep notes or "words of wisdom" that I come across for our car, that I may not neccessarily need @ that time, but realize it's "good to know." I didn't come up w/ this & I don't remember where I found it.

Basically, we've got ~17 gallon tanks on our cars & Mitsubishi has a bad track record w/ pinning the gas needle on any of their cars for that matter. If you're needle is resting @ the bottom well below "E" & you only put in 12 or 13 gallons, this'll help!

My notes come from 2x places, will post seperately... if this came from you, or you know who... give us a link & thanx 4 the info :)

- J

Project Overview/Theory:
To best understand the theory, we will start with the FWD, since it works the same but has fewer parts. The gas gauge in the 2G FWD works as follows: Power from the battery flows through the gauge in the dash, through a yellow wire to the "sender" unit, and through the sender to ground. Now, the sender is a variable resistor, who's value is controlled by the float. When the float is all the way "up" and the tank is full, the "resistance" is low (4 Ohms). When the float is all the way down, and the tank is empty, the "resistance" is high (106 Ohms). The dash gauge simply displays the resistance of the float sender, against a scale of "E - - F".

The "Idiot Light" is a SEPERATE circuit, and has NOTHING to do with the gauge at all. You could completely remove it and the gauge would still function and vice-versa. The "Light" works similar to the gauge. Electricity flows from the battery (+12V) through the light, to the sender, and then to ground. In this case, the sender is a Thermistor. A thermistor is a lot like a switch - when it is submerged in fuel its resistance is very high, when its in air it is very low. So, since the thermistor hangs about 1/2" off the bottom of the tank, when you have 1/2" of fuel left (2.5 gallons) and the thermistor is not being sloshed under fuel constantly, its resistance falls to near zero, current flows, and the light lights up.

Now, several people have advocated moving the needle on the gauge. Well, that works sort of. All you have really done though is move the problem from one end of the scale to the other. Now your gauge will read F for ever when you fill up, and then drop quickly to E. I wanted a better solution.

Our problem is that when the valve (sender) is in the highest resistance state (tank empty) the water meter is not reading enough current flow. This is the fix - we create a leak before the sender. Put a small hole in the pipe, so now more current can pass the meter, which will cause it to read lower, and more accurately represent the amount of fuel in the tank (none).

In reality what we do is to wire a small "variable resistor" between the power wire from the gauge to the sender, and connect the other end to ground. This allows MORE current to flow through the gauge, and gives it a place to go (to ground).







Here's the 'Project' Part, if you can even call it that. Materials required: Soldering iron, solder, 1000 Ohm (1K Ohm) trimmer pot, 2' of wire, 2 "Scotch lock" wire tap connectors (RS #64-3052, $1.69 for 10).

Remove the back bottom seat from the car. (Pull tabs and lift) Under the passenger side you will find a small metal "door" and a white wire loom going to it. Unscrew the white wire loom cover and un-tape it from the wires. Locate the YELLOW (no stripes, just little silver tick marks) wire, and the thick black wire. Now, go inside and assemble your fuel tank adjuster as shown below.







Cut or break off the last terminal, solder one foot wires to the other two. Cover everything with electrical tape, and leave the screw sticking out. Connect one end to the yellow wire in the car, and the other to the thick black one. DON'T cut the wires in the car, simply splice into them with the scotch locks. (wire taps)
Reassemble the wire loom guard, but leave your adjuster hanging out into the rear seat foot well. (You will need to adjust it).

Now, to adjust it you MUST run the car out of gas. People have asked a zillion times for a "magic number". Well, there isn't one. The gauge is finicky and each car I have done is somewhat different. I suggest doing this mod when you are already close to running out (light has been on for at least 20 miles or more).
Now, put a 1gallon gas can in your trunk ($4 at K-Mart) with a gallon of gas in it. And drive until you feel the car running out (you'll know). Once it starts to stumble (usually around a right hand curve or up a hill) pull over and shut it off. (try to park in a fairly level area) Turn it back ON, but don't start it. Now, get out a small screwdriver (you DID remember to bring it, right?) and turn the adjuster ONE TURN CW to raise the needle, CCW to lower it. YOU MUST WAIT AT LEAST 1 MINUTE FOR THE GUAGE TO REGISTER. Now repeat if necessary. I had to go 3-4 turns. Take your time!

Once you think you have got it where you want it (I put mine 1 needle below E) WAIT another couple minutes to be sure the gauge is settled. Then get out and dump in your gallon of gas and go to a gas station.

You are finished! Once you have driven all the way to E and are happy with the results, tuck the adjuster up into the wire loom, tape it up, and you are done.

In the FWD cars there is a ~16.5 gal tank, one sender/pump/light_sw unit on the pass side.

Electrically, the FWD car's sender reads 4 ohms Full, and 112 (+-6)ohms
Empty. The light circuit is TOTALLY separate consisting of a thermistor hanging in the tank about 1" from the bottom. When covered in fuel its resistance is high and the light is off. Uncovered its resistance drops after a few minutes and the light comes on.

Here's the fix and reasoning:

Something is messed up because the senders are supposedly correct (within spec). Together they present the correct resistance to the dash gauge, which is nothing other than a heavily damped ohmmeter. Reasoning that my tank reads correctly when full, but gets progressively more inaccurate as it empties (reads E when I still have 1/4 tank) I figure the problem is that the gauge is not SCALED correctly to the senders (in an electrical sense) there are two possible fixes:

1) Bend the rods for the floats. Not a good idea because now the problem will simply shift to the other end of the scale - ie. the gauge will read high until it finally hits E where it will be accurate. Maybe. Because nothing has been done to correct the scale (shrink it) the problem has just been moved. Considering the trial and error necessary, the fact that the gauge will still not read right most of the time, the fact that the senders are in spec, and not wanting to smell like gas anymore, I abandoned this approach.

2) Fix the problem electrically: The resistance of the senders can be rescaled and adjusted easily by adding resistance in parallel to the WHOLE sender assembly. Using Ohms law and running a bunch of calculations (not detailed here, email if you want them) I figured that I needed to 'add' 4 gallons to my gauge when it shows empty, without affecting the F reading (much) by adding a parallel resistance of 'about' 380 Ohms.

**** Actual fix for 2G gauge that reads LOW ****

Wanting the ability to easily tweak this, I went to Radio Shack and bought a 1000 Ohm potentiometer (15-turn trimmer $1.49, email for part no.), I cut one leg off, soldered on two wires, and spliced them into the harness under the back seat where it passes into the floor and into the senders. You don't need to remove the access hatch, just the white 'wire loom' thing screwed to the floor. You want to put the potentiometer across two wires: Yellow (no stripe - its the sender 'total' wire on both AWD and FWD) and the big black (no stripe) one (Ground). Use those blue plastic 'wire taps' (you don't want to cut the wire, just to wire this across two wires). I left a foot of wire hanging from the potentiometer so I could let it hang in the rear foot well for easy adjustment with a screwdriver.

I pre-adjusted it using a multi-meter to 380 Ohms before installing it, and whaddya know, it moved the gauge exactly the amount I wanted. I have been driving for two days now, and am waiting to run out of gas so I can truly adjust it accurately. Once I get it perfect I will simply tuck the potentiometer up under the rear side panel somewhere. Not bad for $1.49, 10 minutes work, and not smelling like gas.

BTW, when 'adjusting' the pot, the gauge takes a LONG time to register the difference (minutes) so go 1/4 turn at a time and drive a while.

Without reading all that, did you score it from Corbin? I think he might have done a write-up on that, but I'm too lazy to go looking for citations for your term paper here. :shrug

I don't understand why anyone would bother with this mod. My light comes on just before empty. If I get gas at the next station I see after the light first comes on, I find that I can generally only get 13.9gal in the tank. Take a 16.9gal tank, subtract 13.9 and you get 3.0gal. Now, if you figure you get 30mpg, it's a safe bet that you can drive another 90 miles after that light comes on. 50 at the least.

I'd rather leave it as is and more or less ignore the gauge until the light comes on. Then I know I have to stop and get gas, but that it can wait until after work or on the way to work in the morning, or after work the next day, etc..

Just my two cents. Anyone else see things my way on this one? I like the low fuel dummy light. Makes this dummy's life just that much easier. :P

It's from here:

http://www.geocities.com/CapeCanaveral/Cockpit/6144/DSM_Home/2G_Fix_It_Center/flakey_gas_guage.html

If you actually like knowing how much gas you have, it's a worthwhile mod. ;)

Originally posted by DR1665
go looking for citations for your term paper

Ouchy, that was kinda harsh :wallbash

Either way, it's an annoyance... for those of us that don't want to drive another 100miles AFTER the needle is resting well below "E" on the peg, this is for you.

P.S.
Thus the reason 4 my disclaimer "I didn't come up w/ this & I don't remember where I found it."

Use it or not @ your will,
THANX 4 THE LINK FUCKING DUMBASS, PROPS!!!
ERrrrrrrrr, ducking fumbass, lol... nice :)
- J :cheers

I remember reading this way back in the day off dsm.org. Good to have it around again... some people are very "sensitive" about their fuel gauges.

Thanks for finding it.

I was on E last night, filled it up with 14 gallons. I might try it when get bored.

/copy, paste, printed, stored in file in cabinet for a rainy day

"It's all good" :cheers

1x thing I always wondered about is, how come mod's don't ever sticky anything here? I understand that it's quite a bit of work for someone to get it up on the 2gnt.com homepage writeups, but it'd be really easy to sticky... that way peeps don't have to weave through pages upon pages of search results. Are mod's instructed not to sticky so it doesn't get "carried away?"

Just a thought :afro,
- J

If we stickied everything that was interesting or worthy of note, we'd have pages of stickies and new posts three pages back. We usually copy them to the main site or move them to "Things We've Seen Before". Either way, the search function can find it.

This is fairly low on the list of important shit to know. If everything as important, or more important, than this were to be stickied, the new posts would start on page 20 or so.

No, no... I wasn't trying to imply that this should be stickied (don't think so), I was just wondering Y there weren't any period... seeing how it takes so much to get it on the main page. The forum search just doesn't always seem to be the world's best archiving tool.

Seeing how the main site is driven off of PHP Nuke already, maybe the Submit News module could be opened up for peeps to write articles. It would only require a Moderator to approve submissions rather than an admin having to recreate info on forum or moving to things we've seen before.

Don't worry about me, work is slow now & I'm bored :|
- J