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Fuel Gauge Problem

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dklawson said:
Move your tests to the gauge itself and focus again on the green/black wire. You're not looking for a short of the green/black wire... that would produce a reading of Empty. You're looking for an 'open'. Look for a break in the green/black wire, run a new test wire between the tank and gauge if necessary.

Return to the gauge case ground itself also. I know you said it's secure, but make sure that both ends of the gauge's ground wire (gauge and chassis ends) are clean and making good contact. Add another ground just as a check.
Click to expand...

I will follow up on the second paragraph. I already did run a lead from the sender to the gauge with the same result as having the grn/blk wire connected, the gauge goes full tilt.

I believe the ground at the gauge is good because the lamp works when it's connected and doesn't when it's not, but I will run a ground lead to see the results.

Thanks everyone for your input, because I'd be at a loss without it.
 
/bcforum/images/%%GRAEMLIN_URL%%/iagree.gif DK there is something amiss with the wiring.---Keoke
 
Keoke said:
/bcforum/images/%%GRAEMLIN_URL%%/iagree.gif DK there is something amiss with the wiring.---Keoke
Click to expand...

Not the gauge? That is some comfort, I will continue sorting it out. Thanks
 
Well we do not know for sure Dave, as you did not follow my instructions for checking the gage out I posted earlier. go back to my 1:30 AM post and see if the meter functions I suggested you check agree with Dave R's post.---Keoke
 
Keoke said:
Wel we do not know for sure Dave, as you did not follow my instructions for checking the gage out I posted earlier.
Click to expand...

Gosh, you are right! I need an excuse to leave work early, so I will go try that right now, I'll post back in a 1/2 hour, or so.
 
dar100 said:
Keoke said:
Dave , what happens to the meter when the Grn/Blk wire is disconnected from the sender and then grounded?. What does the meter show with the Grn/Blk wire just disconnected from the sensor? --Keoke
Click to expand...

About 10 ohms. BUT, not when the grn/blk wire is disconnected from the gauge, then it doesn't register...no connection.

What do you think?
Click to expand...

Maybe I misunderstood this one. When I disconnected the grn/blk wire at the sender and checked for resistance BETWEEN the grn/blk wire (at the sender end) and ground, the meter registered 10 ohms. With the grn/blk wire also disconnected from the gauge, there was no resistance.
 
Yep you misunderstood what was being asked. It was intended to only monitor the fuel gauge performance when the Blk/Grn wire is disconnected from the sender and when it is shorted to ground. There was no request for resistance readings.---Keoke
 
OK!

When the blk/grn wire is disconnected from the sender and shorted to ground the gauge comes off the empty pin and reads "empty".

When a jumper is installed from the sender to the blk/grn post on the gauge, the gauge reads past full to the pin.

You're toying with me, aren't you? /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
Dave

You still messing with that fuel gauge..still telling you the easiest way to fix it is replace with a NOS "stick".
My e-type has the same problem and while it's fairly simple to correct it continues to fall to the bottom of my list of todo's.
 
Dave,
You are close to figuring it out. You have already verified that your gauge is working perfectly and you have also proved that the wire from the sender, back to the gauge is working perfect.
That only leaves two things;
1..The grounding of the sender to the frame ground of the car.
2..The sender itself is open and will need to be repaired or replaced.

To check the grounding of the sender, loosen one of the mounting screws, strip off some insulation from that test wire you were using before and wrap it around the loosened screw, then tighten the screw back down. Strip the other end of the test wire and find a screw on the body or frame that you can loosen and the wrap the other end of the test wire to and then also screw it down. You could use the battery switch ground bolt if nothing else jumps out at you. Now you have the sender properly grounded to the frame. With the normal connection put back from the gauge onto the sender, test the operation of the gauge. If it now works, your sender to frame ground is no good. If you do this test and the gauge still shows full or past full then the sender is open and will need to be replaced.
 
BIBBER said:
Dave

You still messing with that fuel gauge..still telling you the easiest way to fix it is replace with a NOS "stick".
My e-type has the same problem and while it's fairly simple to correct it continues to fall to the bottom of my list of todo's.
Click to expand...

Years ago, a friend taught me to fly on a little canvas covered wood frame plane of some sort. The gas "gauge" was a metal rod that projected up through the filler cap of the tank on the nose of the plane, the other end of the rod had a cork on it that floated on top of the gas!
 
Ed_K said:
Dave,
You are close to figuring it out. You have already verified that your gauge is working perfectly and you have also proved that the wire from the sender, back to the gauge is working perfect.
That only leaves two things;
1..The grounding of the sender to the frame ground of the car.
2..The sender itself is open and will need to be repaired or replaced.

To check the grounding of the sender, loosen one of the mounting screws, strip off some insulation from that test wire you were using before and wrap it around the loosened screw, then tighten the screw back down. Strip the other end of the test wire and find a screw on the body or frame that you can loosen and the wrap the other end of the test wire to and then also screw it down. You could use the battery switch ground bolt if nothing else jumps out at you. Now you have the sender properly grounded to the frame. With the normal connection put back from the gauge onto the sender, test the operation of the gauge. If it now works, your sender to frame ground is no good. If you do this test and the gauge still shows full or past full then the sender is open and will need to be replaced.
Click to expand...

Well, then it's the sender, because I've already done what you describe to check the ground of the sender, thanks to one of Keoke's posts.

I've got plenty of cork on hand, so the sender is coming out. I'm just a bit confused by the 37 ohm reading on the sender, which would seem indicative of 1/2 tank of fuel.

What do you mean, exactly, when you say the sender is "open"?
 
"What do you mean, exactly, when you say the sender is "open"? "

Take a look at the PDF I posted the link to earlier. There are some pictures of a 0-90 Ohm Smiths sending unit in there. You'll see that the float arm moves two "wipers" over a cylinder wrapped with coils of wire. The wire is one continuous coil of resistance wire which is connected to chassis ground (case) on one end. The wipers rub over that coil as the float arm moves up and down which effectively changes the resistance you measure across the sending unit terminals. If one of the resistance coils is broken you have an "open" circuit, no current can flow through the sender or gauge. This can create the situation you're seeing. So can a bad ground from the sender to the car's chassis.

Before we leave the subject of the gauge, let's just confirm one last thing. Remove the green/black wire from the gauge (NOT the sender, from the gauge). Hook a test wire up to that terminal on the gauge, make sure the gauge case has a good ground, and switch on the ignition. With your test wire NOT touching anything the gauge should show "FULL". Now touch the bare end of the test wire to chassis ground. The gauge should go to "EMPTY". If it does, it means the gauge is OK and as others have said the problem is either an open in the sender or the sender has a poor ground connection.

In addition to poor ground connections and broken resistance wires, I've also seen instances where fuel deposits inside the sending unit have isolated a couple of the metal parts in the sender which need to have good electrical contact with each other. You may find disassembly and cleaning of your sender will fix this problem if the problem is not associated with a poor ground or broken resistance coils.
 
Nope I would not toy wid you but it seems that you just proved the meter is ok so your problem lies in the boot either the sensor ground is poor or the sensor is defective.---Keoke
 
DK WE are trying to isolate the gauge from the problem by seeing that it responds correctly when the Blk/Grn wire is lifted from the sender and also when the wire is grounded. His last test seems to quantify that the guage is OK, the Blk/Grn wire is intact and not shorted to ground.--Keoke.
 
This thread is getting so confused, I hesitate to make it worse. Guess I'll jump in anyway. Several folks may be correct, but it's getting confusing to follow.

Dave,
It should not be "that" hard to check. Start at the beginning & follow each step exactly. Do not skip any steps or assume that something must be OK.

Normal connections:
A- Dash unit -
1- Two switched hot wires, green, connected to the gage terminal marked B. Probably the LH terminal as viewed from the front of the gage. (Glass part)

2- One wire, green/black to tank unit connected to the gage terminal marked T. Probably the RH terminal as viewed from the front of the gage.

3- A ground wire from the gage unit to the chassis.

B- Tank unit -
1- One green/black wire attached to the sender terminal.

2- An added ground wire from the sender metal to the chassis.
=======================

Checks:
A- Dash unit -
1- Key on - There should be12 volts from the two green wires to ground. Terminal on gage marked B.

2- Key on - T terminal on gage, green/black wire disconnected, gage should read above full.

3- Key on - T terminal on gage grounded, gage should read empty.
If this checkes the dash unit is OK. If not, there is something amiss in the gage.

B- Sender unit -
1- green/black wire disconnected. Sender terminal to ground should read 70 ohms full, 0 ohms empty. 30 to 40 ohms tank 1/2 full. Remove the sender to check float travel, ohms, & if the float is partially filled with fuel. Make sure that as the float travels there are NO discontinuities or jumps on the ohmeter reading.
If this checks, the sender is OK.

2- Green/black wire at sender disconnected. Key on. Dash gage should read above full.
If the dash gage does not read above full the green/black wire is shorted or partially shorted to ground.

3- Green/black wire at sender disconnected from sender & grounded. Ignition switch on. Dash gage should read empty.
If the dash gage does not read empty, the green/black wire is broken or not making connection somewhere.

PS - Doug - The AH gage & sender are built differently & do not look the same as the MG. They do function the same way though.
Best of "luck"
D
 
He just did that Dave see his last test. The guage responds correctly--Keoke
 
He did a partial check. I just summed up the previous & added some about the connecting wire & tank unit.

If you think I'm cluttering things up, I'll be glad to remove the post. What say you?
D
 
Join the crowd.---Keoke-- /bcforum/images/%%GRAEMLIN_URL%%/grin.gif
 
Dave -

Your post is very good. keep it.

The only next step is to yank the sender out and then light up a cigarette and see if there are any gas vapors around....
 
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