Fuel gauge still not working, What am I missing? Options

[stugray]

Just learned the dialectric constant of water is way higher than gas, so my water test was pointless.. who knew

This should only matter if the fuel level sender is the capacitive sense type.
This one has a moving float right?

ANd the pic directly above is not correct.
You have the +12V hooked up and the Sense "S" hooked to the gauge GND, but the gauge is not hooked to car GND.

And the fact that it worked in the water, but not in the gas (in the tank) points to a grounding issue.
When you are in the water, the sender body is not hooked to car Chassis, but when in the tank, it is.

[john77]

Thats not a Porsche gas sender (Porsche has 3 connections). Most after market
senders read 90 ohms (empty) 0 ohms (full). Porsche senders are 90 ohms empty
0 ohms full. Try removing the sender from the tank and turn it upside down and
see what happens.

One step ahead of you - see my original post (IMG:style_emoticons/default/smile.gif). Out the tank, hooked up to the gauge, if I flip the sender the needle on the gauge moved as it should.

[timothy_nd28]

That test is almost correct. You jumped out the S to G on the back of the fuel gauge, but you need to have another wire that ties both of them to ground or a brown wire in your dash.

This test was to simulate a 0 ohm condition, and according to the spec of this gauge the needle should of went to empty. I just wanted to confirm that 0 ohms is empty and 90 ohms is full. It seems backwards to me, and that test you did would of verified that.

Another test you can do.. Pull both wires off the sender and ohm each terminal to one of the screws that holds the sender down.

[john77]

That test is almost correct. You jumped out the S to G on the back of the fuel gauge, but you need to have another wire that ties both of them to ground or a brown wire in your dash.

This test was to simulate a 0 ohm condition, and according to the spec of this gauge the needle should of went to empty. I just wanted to confirm that 0 ohms is empty and 90 ohms is full. It seems backwards to me, and that test you did would of verified that.

Another test you can do.. Pull both wires off the sender and ohm each terminal to one of the screws that holds the sender down.

Ha, okay, done that now. Yep, the needle just reads empty.

[timothy_nd28]

K, now measure the sender unit. Measure the resistance between either terminal to ground. Then measure the resistance between both terminals.

[john77]

K, now measure the sender unit. Measure the resistance between either terminal to ground. Then measure the resistance between both terminals.

Between the terminals is showing 2.3 ohm.

Sender wire terminal grounded is showing 116.5

And the ground terminal to ground is showing 118.4

[timothy_nd28]

All wires off the sender while measuring?

[john77]

All wires off the sender while measuring?

Haha, no. Oh boy, I'm really showing my skills here. Both failed to give me a reading and when I tested for continuity (?) neither gave me a tone.

[timothy_nd28]

Ok, so all wires are disconnected at the sender and you read infinite resistance between both terminals?

[john77]

Between both terminals I get 2.3 ohm.

From either of the terminals to a ground is infinite.

[timothy_nd28]

K, 3 ohms should reflect an empty tank. Dumb question, how much fuel do you have in that tank?

[Dave_Darling]

And the ground terminal to ground is showing 118.4

That sounds like a real problem there. If you have more than a few ohms resistance between something that is supposed to be grounded and something that actually is grounded, you have a problem...

--DD

[stugray]

I will try again:

"I pulled the sender, wired up a new ground and hooked up a new wire from the gauge to the sender and tested the sender manually by turning it upside down and then back. "

If you can turn the sender upside down and have it change resistance, then it is not a capacitive type sender.
So:
"Just learned the dialectric constant of water is way higher than gas, so my water test was pointless.. who knew "

This should not matter.
You can make it work in the water, but not in the car (gasoline).
SO when you put it in the car, you are somehow shorting out the sender unit.

Try swapping the wires on the sender unit.
One of them is probably grounded to the sender case.
The other is the variable resistance.

If it is hooked up backwards, it will work in the water, but not in the car.

[john77]

K, 3 ohms should reflect an empty tank. Dumb question, how much fuel do you have in that tank?

The tank is 4/5ths full.

[john77]

I will try again:

"I pulled the sender, wired up a new ground and hooked up a new wire from the gauge to the sender and tested the sender manually by turning it upside down and then back. "

If you can turn the sender upside down and have it change resistance, then it is not a capacitive type sender.
So:
"Just learned the dialectric constant of water is way higher than gas, so my water test was pointless.. who knew "

This should not matter.
You can make it work in the water, but not in the car (gasoline).
SO when you put it in the car, you are somehow shorting out the sender unit.

Try swapping the wires on the sender unit.
One of them is probably grounded to the sender case.
The other is the variable resistance.

If it is hooked up backwards, it will work in the water, but not in the car.

Sorry Stu, I keep checking back on this on my phone and completely missed your first reply.

The sender is an aluminum shaft with a float inside it that appears to run up and down a circuit board. This is the unit:

http://www.fuelsafe.com/store/sending-unit...oline-only.html

Maybe I'm misunderstanding how the sender works, but when I put it in a bucket of water the ground terminal on top of the sender was wired to a ground on the chassis. Isn't that how it grounds?

The shaft doesn't seem to touch the tank - it's smaller than the hole, the top of the sender is plastic, and there's a gasket between it and the tank.

When I asked the guy from Fuel Safe if the sender touching the metal of the tank would be a problem he said:

"The outside aluminum shell or shaft of our standard senders is grounded so touching the side will not hurt anything as long as the ground wire is on the correct lug or terminal. The ground will have a G by it."

I tried swapping the wires into the sender as you said and now the needle has gone all the way over as far as it can and has stayed there, even with the ignition off. If I swap the wires back on the sender it makes no difference, the needle just stays there.

[john77]

Okay, now that's all the gauge will do.

If I jump the ground on the back of the gauge to the sender lug it takes the needle back to E. But when I wire it back up correctly with both the wires the correct way round it just shoots up past F as far as it can go and just stays there, even with the ignition switched off.

[timothy_nd28]

The problem was with the sender unit. You measure 2.3 ohms between both terminals on the sender (with the sender installed on the tank). 2.3 ohms on this sender means empty tank. You then measured both pins to one of the mounting scews that fastens the sender in place. You reported back that the resistance readings was infinite. This shows that the sender is electrically isolated to ground, which is what I expected.

Again, the sender is installed, reading 2.3 ohms, yet you had 4/5th worth of gas in your tank. This was the issue. The gauge was only reading what the sender said. If you sender was reading 90 ohms, I'm sure your gauge would of read full.

The float on the sender is sitting at the bottom, and not floating. I'm not sure what's going on with that. 4/5th worth of gas should had the float pretty high up, and a reading 80 plus ohms. 2.3 ohms means the float is sitting or hung up at the bottom.

I'm not sure what you just did, but I'm afraid you may have just ruined the gas gauge, which happened to be the only part that was working. Your issues lay with the sender.

[john77]

The problem was with the sender unit. You measure 2.3 ohms between both terminals on the sender (with the sender installed on the tank). 2.3 ohms on this sender means empty tank. You then measured both pins to one of the mounting scews that fastens the sender in place. You reported back that the resistance readings was infinite. This shows that the sender is electrically isolated to ground, which is what I expected.

Again, the sender is installed, reading 2.3 ohms, yet you had 4/5th worth of gas in your tank. This was the issue. The gauge was only reading what the sender said. If you sender was reading 90 ohms, I'm sure your gauge would of read full.

The float on the sender is sitting at the bottom, and not floating. I'm not sure what's going on with that. 4/5th worth of gas should had the float pretty high up, and a reading 80 plus ohms. 2.3 ohms means the float is sitting or hung up at the bottom.

I'm not sure what you just did, but I'm afraid you may have just ruined the gas gauge, which happened to be the only part that was working. Your issues lay with the sender.

Yep, looks like the gauge is ruined, I pulled the sender and now when I invert it the needle just sits there. As an aside, the float is free moving, and was free moving in the water, so I have no idea why it's not floating in the gas.

Thanks for your time and patience on this Timothy, I appreciate it. I'll speak to the manufacture tomorrow and see what his prognosis on the gauge is.

[timothy_nd28]

Since you have the sender out, go ahead and invert it while measuring the resistance on the 2 pins. You should read 90 ohms.

Now, put the sender right side up, you should read 0 ohms. Slowly insert the sender back into the fuel tank. You should see the resistance rise. With it all the way down, you should read 70-80 ohms, if not,,try shaking the sender.

[stugray]

The website agrees with timothy_nd28 that the sender should read 0 Ohms when empty.

This is exactly the same as grounding the sense wire to the car GND.
So without the sender in the picture at all, what does it read if you hook:
+12V to +12V
GND to GND
Sense to GND

It should read empty.
Unhook the sense wire (open) and it should read Full.

If the gauge does not do that it is broken or the description of the unit from the website is wrong.