Fuel gauge issues

[Larry E]

Please tell me why or what I can do to correct this situation with my fuel gauge. I have replaced all of my gauges with Equus white face gauges GM type 0-90 ohms on the fuel gauge. I have also installed the appropriate Equus sending unit (0-90) ohms. I have the gauge grounded along with the sending unit. The sending wire goes from the sending unit to the proper connection on the fuel gauge as does the power lead from the Ignition switch with key on. The other gauges work as does the lights even on the fuel gauge the light works.

OK so WHY????? Does the fuel gauge needle peg past full when I turn the key on? It even does that when I unplug the sending unit wire. I have replaced the new gauge with another new one.

SO WHY???? What am I missing here?

Larry E

 

[Cheetah 210es]

Re: Fuel gauge issues

Sounds like a bad earth.

 

[MolsonCanadian]

Re: Fuel gauge issues

Yep, sounds like a bad ground to me too. If I recall correctly the sending unit must also be grounded.

 

[Larry E]

Re: Fuel gauge issues

Yep, sounds like a bad ground to me too. If I recall correctly the sending unit must also be grounded.

I would think that too but I have a ground wire running from the ground to one of the mounting screws on the sending unit flange. I am going to pull the sending unit and see if the float arm is touching the body of the sending unit. For some reason in the instructions they are emphatic about this not being.

PS thanks boss for changing my thread title. WHY was kind of dumb...

 

[Silvertip]

Re: Fuel gauge issues

A fuel gauge will peg full if the "S" terminal on the gauge is somehow grounded (either internally in the gauge or externally). In fact that's one of the tests for the gauge itself is to momentarily ground the "S" terminal. I seriously doubt that's the issue however since you replaced the gauge. Testing the integrity of the wire from the gauge to the sender should be done by disconnecting both ends of the wire. Using an ohm meter check for continuity between the wire and ground. If it shows continuity that wire is at ground potentional and hence the gauge reads full. You can also have a bad sender but that can be checked with an ohm meter as well. Remove it and connect the ohm meter between the threaded terminal and the metal shell of the sender. Move the arm through it's travel. If it doesn't transition smoothly between 0 & 90 ohms or shows very low resistance through its travel it is the culprit. Lastly, yes, if the float arm is hitting the side of the tank it certainly will will affect the reading.

 

[Larry E]

Re: Fuel gauge issues

A fuel gauge will peg full if the "S" terminal on the gauge is somehow grounded (either internally in the gauge or externally). In fact that's one of the tests for the gauge itself is to momentarily ground the "S" terminal. I seriously doubt that's the issue however since you replaced the gauge. Testing the integrity of the wire from the gauge to the sender should be done by disconnecting both ends of the wire. Using an ohm meter check for continuity between the wire and ground. If it shows continuity that wire is at ground potentional and hence the gauge reads full. You can also have a bad sender but that can be checked with an ohm meter as well. Remove it and connect the ohm meter between the threaded terminal and the metal shell of the sender. Move the arm through it's travel. If it doesn't transition smoothly between 0 & 90 ohms or shows very low resistance through its travel it is the culprit. Lastly, yes, if the float arm is hitting the side of the tank it certainly will will affect the reading.

Thanks that is great information. One thing I am confused about and that is if I disconnect BOTH ends of the sending wire what does that show if I use my Ohm meter to check for continuity between the wire and ground? The sending unit is new along with the gauge. So tomorrow I will pull the sending unit and see if the float arm is touching the housing of the sending unit. As I stated before the gauge pegs even with the sending unit wire disconnected so that really confuses me. OH well it is only a wiring problem I am sure it will straighten out sooner or later...I do not give up easily.

Larry E

 

[Silvertip]

Re: Fuel gauge issues

Checking the send wire verifies that somewhere along its length it NOT grounded (i9nsulation pierced by a screw or sharp edge of metal). Guessing is not a way to troubleshoot. You troubleshoot by VERIFYING. Leaving anything to chance is usually a good way to overlook the real problem.
1) Verify you have +12 volts on the gauge with the key on.
2) Verify you have a good ground on the gauge. If you have other gauges and they work, usue your ohm meter to measure between ground on the fuel gauge and ground on any other WORKING gauge.
3) Verify the send wire as I explained.
4) Verify the metal shell of the sender is grounded. Measure with the ohm meter between the shell and the negative post on the battery.
5) Verify the sender is tracking 0 - 90 ohms.
6) Verify the float arm is not hitting the side of the tank and that is moves smoothly.
7) Verify that the float actually floats.
8) Verify that you have not tightened the send wire so much that the stud has spun which creates a short between the stud and the metal shell of the sender. Follow these steps and the gauge will work (assuming you replace or fix what isn't right) and that you test properly.

Here is a picture of what happens when you overtighten the sender wire stud. (1) is the insulator that separates the stud (2) from the metal shell. (3) is a connecting tab that is under the head of the stud (2) and connects to the variable resistor. If the stud turns, it spins spins the connecting tab (3) from the resistor so it touches the metal bar (4). You now have the sender terminal shorted to ground and zero ohms = full on the fuel gauge.

 

[Larry E]

Re: Fuel gauge issues

Checking the send wire verifies that somewhere along its length it NOT grounded (i9nsulation pierced by a screw or sharp edge of metal). Guessing is not a way to troubleshoot. You troubleshoot by VERIFYING. Leaving anything to chance is usually a good way to overlook the real problem.
1) Verify you have +12 volts on the gauge with the key on.
2) Verify you have a good ground on the gauge. If you have other gauges and they work, usue your ohm meter to measure between ground on the fuel gauge and ground on any other WORKING gauge.

For sure you have gone beyond the call of duty. I will do everything you suggested. The sending wire is only about 3 feet long because the tank is under the bow. So I have already checked with an ohm gauge the continuity of that wire. I have a terminal strip with the main ground wire from the engine and then each post is daisy chained on the strip. Then I have all the gauges coming off of this terminal strip to their corrospoinding ground stud. Same with the Ignition hot wire. I am going to remove the sender again because for some reason I suspect it. You know I will keep you informed right? Still not sure why the gauge does the same thing even with the sending wire disconnected.

Thanks again for your patience and replies
Larry E

 

[Silvertip]

Re: Fuel gauge issues

Still not sure why the gauge does the same thing even with the sending wire disconnected.

Larry E[/B]

I missed the part about the gauge pegging with the send wire disconnected. That then verifies the the "S" terminal on the gauge is indeed grounded in some fashion (either inside the gauge or externally). Something in your wiring is bad or you have received two bad gauges. If you know how much fuel is in the tank, disconnect the send wire at the gauge and measure the resistance to ground. With a full tank resistance should be zero or near zero. 1/2 tank would be about 45 ohms and 90 ohms or so with an empty or near empty tank. That would prove the sender and the wire is ok and the problem is the gauge or the gauge wiring.