aftermkt. fuel gauge prob OR sending unit prob ???

[Kevin Wiles]

Got my 0 ohm empty / 90 ohm full autometer gauge in the mail.

 

installed it per instructions

 

Turned key, and needle on gauge shoots up waaaaaay past full (imagine empty is 10 oclock and full is 2 oclock) MY NEEDLE IS AT 5'OCLOCK

 

 

See my problem ??

 

please note that after i remove the key, the needle comes back and rests at empty like it should.

 

it is getting power, the multimeter reads 11.3 volts if you hold the black lead to the center terminal and the red lead to the terminal on the right (if you're looking at it from the back)

 

the brown wire (aftermarket wiring harness) coming from the fuel sending unit goes to the terminal on the left (again looking at the back of the gauge)

 

not sure how to use the multimeter to read ohms because there is about 5 settings (2000,20k,20 etc.) so I tried to read it from any and all of the settings until I got the desired results (trying to get a number between 0 and 90) and preferrably close to halfway between those numberst because i have a feeling the tank is half full.

 

But no matter what setting, I couldn't get a proper reading. On the middle setting of the multimeters ohm function i got a reading of NEGATIVE 6, and on the same setting with the key out, I get POSITIVE 0.32

 

I remember after i painted the gas tank, making sure the connection was good for the brown sending unit wire and making sure the ground wire connection was lookin' good, but that has been 3 years ago, but undisturbed since then. I can't imagine that coming loose or anything.

 

Whats going on here? bad sending unit? can anyone shed some light on this or help me by letting me know how to test my sending unit or use my multimeter

 

 

[bobsmc]

set your meter on the 200 ohm scale and you should get a reading between 0-90 at the brown wire off the fuel tank, depending on the amount in the tank.

it sounds to me like your ground wire is not making good chassis ground.

thats where i would start.

 

[Kevin Wiles]

i think i might have found a problem. I THOUGHT that i had followed the instructions when i installed the wiring harness but I just downloaded the autogage instructions (mine are autometer, but that shouldn't matter for this) It says that the ground should go all the way back to the tank at the sending unit.. If I recall correctly I grounded the sending unit to the body, and grounded the gauge to the roll bar. Could this be my problem????

[kc8oye]

if it shoots to way past full, there is an open circuit to the fuel gauge.

 

grounded = empty.. 90 ohms = full. .any more then 90ohms and off the scale she goes.

 

open circuit is infinite resistance. I would make sure the sending unit is properly grounded.

 

check the resistance at the tank by measuring from the brown wire to ground, it could be as high as 100ohms.. if that's good, reconnect the brown wire.. check at the other end by the gauge..

check from the wire to the body, and also from the wire to where you grounded the gauge.

 

[Kevin Wiles]

This morning I ran the ground wire all the way from the sending units ground wire to the back of the gauge per the instructions (instead of pigtailing each to the body) ok I took some more readings, this time with the multimeter on the correct setting.

 

heres what I checked.

 

TANK IS FULL

 

1. with NO wires connected to the gauge, 114 ohms at gauge

2. IGNITION OFF with WIRES CONNECTED, 114 ohms at gauge

3. IGNITION ON with wires connected, checking at gauge -nothing. the multimeter just reads "1" all the way to the left of the screen (it does this when the leads are touching nothing)

4. IGNITION OFF with wires connected, 114 ohms at brown wire that comes from sending unit (haven't dropped the tank, but i'm taking the reading from the wire as close to the sending unit as possible)

5. IGNITION ON with wires connected, NOTHING when checking from near sending unit at rear of car.

 

 

So in conclusion, i'm getting ohms with the ignition off (which seems normal) but as soon as I turn the key, nothing.

 

 

[Mike 57]

Kevin, if you are measuring resistance (ohms) with the key on you may be puttin current across the meter and the meter does not like that.

[Kevin Wiles]

hey mike i admit i do not know much about electronics

 

but isn't the current coming from the other wire to the gauge? (yellow)

 

theres a yellow wire from a switch power source that reads 11.6 volts with the key on and 0 with the key off. this yellow wire goes to the terminal on the right (if looking from the back of gauge) In the instructions it says in bold print NOT to touch this wire to the terminal where the brown wire goes, or else it will be damaged. This tells me that IF any current goes to the brown wire terminal on the left, thats BAAAD.

 

again, the black wire is the center terminal on the back of the gauge and as of today, goes all the way to the ground wire on the sending unit.

 

should i check and see if I have voltage on the brown wire with the switch on? if I do I'm guessing thats bad?

[kc8oye]

you can't measure resistance with current flowing in the circuit.. multi-meter's don't like that.

 

if you are getting 114 ohms at the gauge, and the gauge isn't working, it's either the ground to the gage, or the gage is junk.

 

try grounding the terminal to the gastank sender and see if the gauge will pull down to 'e'

 

[Kevin Wiles]

how is there current flowing in the brown wire circuit? if the ohm meter can't measure the resistance with the ignition on, how can the gauge?

 

oh i have so much to learn.

 

whats funny to me is that i can get 114 ohms at the gauge with the multimeter with the ignition off

 

what whats funnier is if you take the gauge all the way out, sit it on the work bench and with no wires attached, measure 114 ohms on the multimeter.

 

KC, you say try grounding the terminal to the sender and see if the gauge will pull down. i have already grounded the center terminal on the gauge to the black wire that comes off the sender. is that what you're talking about?

 

i'm trying to hang in there, but i'm getting frustrated. please bear with me here.

 

it should simply just work. it SHOULD BE just this simple:

 

1. brown wire from sender to left terminal on gauge.

2. black wire from sender to center terminal on gauge.

3. yellow wire marked "fuel gauge" from aftermarket wiring harness to right terminal on gauge.

 

and thats what I've got. but not working properly

 

here are the directions:

 

 

Fuel Level

Gauge Specifications

MODELS 2315, 2316, & 2320

NOTE: For the following installation THE GAS TANK MUST BE FULL!

1. Disconnect negative (-) battery cable. (Wear safety glasses)

2. Gauge uses vehicle's stock sender in fuel tank. Existing wires may be

used or route proper length of 18-gage, 2 conductor wire from fuel tank to

gauge. Connect one end to terminal post on fuel level sender and the

opposite end to the sender terminal post (S) (on left) on back of gauge. See

figure.

3. Connect wire from negative (-) center terminal post on back of gauge. to ground

on fuel tank.

4. Connect wire from ignition switch to the positive (+) terminal post on back

of gauge (on right) .CAUTION: Be careful not to touch ignition wire to

the sender terminal (S). This will damage the sender.

5. Snap-in light socket assembly and connect to dash lighting circuit or to

other 12 volt light source. If dash is metal, a ground connection for light is

made when gauge is mounted with brackets provided. If dash is nonmetallic

(or if gauge is cup mounted), a separate ground wire must be

connected from gauge case stud to a good ground.

6. Reconnect negative (-) battery cable and check reading.

This gauge is designed to operate with the original sender in the vehicle's fuel

tank. To insure accurate gauge readings, it is important to measure the

resistance (ohms) of the sender with an ohmmeter at full and empty tank

conditions. Consult table for proper gauge application for your vehicle.

NOTE: Production tolerances in the resistance of some vehicle's tank senders

may cause the gauge to read incorrectly when tank is full.

 

 

 

 

 

 

[kc8oye]

I'm gonna skip the electronics lesson for right now

 

2) which model exactly do you have for the gage?

I'm lookin at the instructions for the 2316 auto gage...

it says to run a pair of wires back to the tank.. this shouldnt' really be necessary (stock gauge didn't)

The wire coming from the tank, I'm assuming it would be your yellow one from the aftermarket harness.. that would go to the "S" terminal

on step 3, any vehicle ground should be just fine as long as your sender is grounded to the chassis.

oook i I see where you went wrong.

 

Left terminal goes to your yellow wire from the tank.

CEnter terminal goes to ground (any chassis ground)

Right terminal has to go to Ignition switched 12v.

 

 

so your brown wire from the tank, should connect to the yellow wire in the harness... the tank's sender should be grounded to the body somewhere.

 

 

[Kevin Wiles]

nah the wire from the tank is brown, and the ground from the tank is black

 

the wire for power under the dash is yellow. there are two of these, and i have both crimped together into one eyelet for the right terminal.

 

the gauge is getting voltage when i turn the key on if i place the multimeters red lead to the right terminal and the black lead to the center terminal. So i don't think the problem is with the yellow wire at all. but i could be wrong. I'm a newbie to all this.

 

i'll check the exact model of my gauge when i get home, at work now.

 

 

 

 

[monte70car]

kevin, i wonder if the gauge could be bad. i dont know much on the aftermarket gas gauge, but its an ideal. the other ideal would be a bad sending unit. i still have to put the dash in our project at home so im not sure if its gauges will be right or not since we did an autowire harness setup for a custom. as of right now im sure the amp gauge wont work as its not wired up.

[kc8oye]

oh ok.. yellow is power ok

with the power off, you are getting 114 ohms from the brown to the black ground wire correct?

 

if you are, I would say the gauge is black.

 

what I was saying, is short the "S" term on the gauge to ground with a piece of wire.. (this simulates an empty tank) if the gauge doesn't swing back to 'E', then the gauge is flakey

 

[wallaby]

The fuel gauge uses a variable ground. The variance happens in the sending unit in the gas tank. Imagine the sending unit as a volume knob; the high volume setting makes your gauge read full and the low volume makes the gauge read empty.

 

Most of the time a volume knob will control the level of voltage coming out of it (like the dimmer switch for your dash lights), but the fuel gauge is different. The fuel gauge has a constant voltage coming out of it and going to the sending unit...and the sending unit controls how much of that current gets to ground.

I guess the good analogy would be a garden hose with a trigger nozzle at the end: Your fuel gauge (the faucet) is preset to be fully on all the time, and you control how much water flows through by moving the trigger (sending unit) at the other end of the hose. I guess we could take it even farther to visualize the water being squirted out of the hose going to the GROUND.

In one position water flows at full capacity to the ground, and at the other extreme no water flows to ground. You have a meter near the faucet (your fuel gauge) that keeps track of the flow rate so you always know what's happening at the other end of the hose.

 

So back to your gauge...Is it true that the terminal going to your sending unit is labeled "S"? (makes sense). Unhook whatever you have on that "S" terminal now. With no wire attatched to the "S" terminal, turn on the ignition key and observe where the needle points. It might not jump to full extreme, but that's ok. Now get yourself a test light and ground one end of it, and put the other end on the "S" terminal. With the key on you should get a different reading on the gauge. Finally, try running a test wire from the "S" terminal directly to ground. This last test should peg the meter.

What we are doing is simulating different gas tank levels to see if the gauge works. The first test is with infinite resistance (no current flow to ground). 2nd test is with SOME resistance (providided by the bulb in your test light so partial flow to ground), and 3rd test is No resistance (full current flow to ground). If the gauge is working it should point to different positions with the different tests.

Your fuel gauge is just an OHM meter labeled E and F instead of 0 and 90.

 

 

 

 

 

[Sam (Bones)]

that is a great explaination

[Kevin Wiles]

Wallaby, I went out and checked everything you said.

 

1. disconnect "s" wire, turn on switch, needle points way past full like always. this tells me that the brown wire isn't really even doing anything as far as resistance goes.

 

2. get test light, ground one end and put other on "s" terminal, needle points way past full again, no change.

 

3. now it gets interesting. put wire from "s" terminal straight to a ground.. the needle immediately goes to EMPTY.

so we've given it a lot of "resistance" and it flies to empty.. thats good, we know that the gauge works.

 

 

 

So after all that I checked a few more things. For some reason, I'm getting 6 volts at the S terminal. That might be normal, but I thought the s terminal was only for restistance wires (like a speaker) So I found that odd. I took the brown wire off "s" and it still reads 6 volts on the multimeter. So at this point I feel like its supposed to be getting this voltage at this term. agree? is this right?

 

 

I got real curious so I took the gauge out of the car, and set-up a car battery on my work bench. I ran alligator clips from neg of battery to the center terminal on the gauge, and another from the posi of battery to the "I" terminal for power. Immediately the gauge pegs way past zero. So again, I'm feeling good that my wiring is good under the dash. THEN i reversed the power wires just for giggles, and the needle jumps to empty> NOW THAT IS ODD i thought. Why is the gauges needle reacting to Voltage??

 

I'm beginning to think more and more that either my brown wire has become disconnected from the sending unit, and i'm going to have to pull the tank, OR the sending unit is bad and I'm going to have to pull the tank

 

so am I correct in these assumptions?

[kc8oye]

honestly, I don't think that gauge is working correctly if it read way-past-full with the test light.

 

[wallaby]

6 volts coming out sounds ok. I really thought that the resistance of the lightbulb in your test light would get a reading from your gauge, but the current might be low enough that it flows without trouble right through the lightbulb.

 

From the sounds of it I think you have narrowed the problem down to something in the rear of the car. If the sender wasn't hooked up to the gauge it would behave exactly as yours is. It sounds as if the gauge is probably ok....it does travel back & forth depending on electric signal.

Check that sender.

[kc8oye]

mark.. he measured 114 ohms on teh wires at the gauge (if I read that correctly).. woudln't that mean his gauge is FUBAR?

 

[Kevin Wiles]

kc you are correct it was 114 ohms on the wires at the gauge, but that was with the switch off.

 

however, for what its worth, you can take the gauge all the way out of the car and put it on a bench and it will read the same 114 ohms at those terminals with nothing hooked to it.

 

The tank is topped off so my next step i think is siphon some of that liquid gold out into a can. Last time I tried that I got a little in my mouth and I tasted it all day. I had to be careful not to burp near an open flame.

 

 

 

[kc8oye]

OHHH dude.. dont' measure the gauge.

with ALL the wires disconnected

measure the brown wire that goes to the tank. measure that to ground.. tell us what resistance you see there.

 

it SHOULd be around 90-100 ohms full.

 

[kc8oye]

it's not unusual to go past full yes.. but not nearly 180° of needle travel past it.

 

[Sam (Bones)]

I know a easy way to fix this....just stop at every gas station you see

 

I KNOW...shut-up SAM!!!!

[Kevin Wiles]

ok UPDATE UPDATE UPDATE

 

the first thing i did when I got home was I popped the trunk of my OTHER monte and tested the ohms from the brown sending unit wire. 43 ohms. so i know that it should work the same way on the coke machine

 

but it didn't.

 

So I siphoned a majority of the gas and dropped the tank.

 

When it came down it was very apparent that the wires were connected snugly and correctly

 

With the tank on the garage floor, i disconnected the sending unit wire and left the ground wire still connected. Still no ohm reading all the way at the sending unit itself. So I thought: sending unit definitely bad.

 

So I pull the sending unit out of the tank.

 

Heres where it gets weird. And heres the answer to all my problems:

 

With the sending unit sitting on my work bench I CAN SUCCESSFULLY READ THE OHMS on the terminal INSIDE the fuel tank, and all the way up that little wire that is inside the tank, but then cannot read the ohms on the little metal snap connector on the outside of the unit.

 

So the problem is that its working BUT its shorting itself out at the snap connector.

 

In fact I could move the float up and down and see the ohms change when measuring from the spot that lives inside the tank.

 

I guess in theory you could fix this by somehow removing the snap connector and putting a new insulating bushing on it.

 

I called my dad and he still has my old tank under his utility building. I called him and had him out there in the dark looking to see if that old tank still has the sending unit in it. It does, and he says it is visually ok. So that one might be going in if it tests ok.

 

Stay tuned I'll have a working fuel gage very soon.

 

 

[Jared Richey]

Kevin,

 

Need help on Saturday? Or any parts?

Let me know.

 

I'll be glad to help.