Fuel/gas Sender problem

[CudaJon]

This one has me baffled.   Let me start off by stating I replaced the VR in the instrument panel and proved that every gauge works before reinstalling the panel.  The fuel gauge never worked when I purchased the 73 Cuda and I was always thinking it was the sender. So I systematically proved that everything worked up to the sensor. I placed a 70 and 10 ohm resistor at the wire where the sender connects and had my daughter read off the gauge. That works!  OK does not seem to be the wiring to the sensor, this is with the ground clip installed between the fuel hose, BTW.  Now I removed the sensor from the gas tank which BTW I estimate about 1/4 tank of fuel in the tank. The sensor mechanism looked brand new, OK well let me measure the resistance of the sender while I have it out so I moved the float around. The float itself was in great shape too and looked brand new, no leaks to cause it to sink. OK,  float all the way up approx 9 ohms, float resting the opposite swing about 72 ohms.  Re hooked the wiring of the sensor without putting it in the gas tank. Gauge checked out OK while I moved the float. Hmmmm ok reinstalled the sender and measured the resistance at the sensor terminal, 72 ohms - empty tank.   Without putting fuel in the tank to prove to myself I have gas what can be the problem?? What am I missing?? Wrong sender for this fuel tank??? One can only install it the correct way since there is a tab to locate the sender correctly. I'm lost on this one.  Another data point, the gauge would always read about little less than a half with a full tank, when it did not work (before I mess with everything) and go down to empty even when I knew gas was in the tank. Any comments would be greatly appreciated.

[CudaJon]

BTW, Happy Memorial day - Let's never, never forget our troops.  God Bless America

[Katfish]

I'd verify the float doesn't have any pin holes.  The ethenol gas eats up the brass.

[jason340]

You may try a temporary ground wire from the sending unit to a good chassis ground just to be sure it is not a grounding issue.

[CudaJon]

I examined the float carefully and actually floated it in gas. If it had tiny holes it would not have a enough time to fill up since I'm pulling the sender in and out of the tank. As far as ground connection. I have a hard wire clip from sender to frame. I know it works cuz I moved the float on the sender before I installed the sender keeping the same ground when installed?  I also bend the arm of the float thinking it's not touching the gas but to no avail.  Could it be a sender for another gas tank.?? The arm looks rather small but need to compare it to pictures of vendors selling these. Thanks for the comments!!

[JayBee]

Here's another "fix" that has been around for these senders. Considering that the only ground for the internal resistor is at the moving pivot point this mod is a great idea. I did it on mine but make sure the wire is long enough as to not interfere with the float's sweep. When you "floated" the float in gas, did you fully submerge it looking for bubbles?


 

[CudaJon]

Hey John,

I did not push down on the float but will and look to see what happens.  I can also try the extra ground strap. Thank you for the picture and comment. I'll keep trying...

[Katfish]

It will be easy to tell if float has holes.
Remove and shake, you'll be able to tell if there's gas inside.

[JayBee]

  That's exactly how I found out one of mine had a pinhole.

[TelisSE440]

Here's another "fix" that has been around for these senders. Considering that the only ground for the internal resistor is at the moving pivot point this mod is a great idea. I did it on mine but make sure the wire is long enough as to not interfere with the float's sweep. When you "floated" the float in gas, did you fully submerge it looking for bubbles?

  That's a really good fix. Just test it with the sending unit out, that will clear up some things...

[JayBee]

   Any updates on this problem.

[CudaJon]

So the result was the fuel sender was not deflective and by just bending the arm with the float and knowing the amount of gas in the tank I was able to get an indication of fuel. It's not perfect meaning it's not 100% accurate but I'm in the neighborhood.

[JayBee]

Good stuff. Congratulations, you are now an expert on e-body fuel system components.   

[CudaJon]

Thanks it's fuel for thought!

[chargerdon]

I have a new Fuel sender unit in my new gas tank on my 74 Challenger..   19 gallon tank.   

When tank completely FULL the gauge reads a little beyond the Full increment and will stay there for 25-40 miles.   I only get 11-12 mpg so this means that the tank will read full even when down 2-3 gallons.    As the fuel is consumed the gauge moves, and when it gets down to E (empty) If i go to station and fill it up it will only take between 11-12 gallons.   This means that the tank still has in it 6-7 gallons when it shows empty.   

I verified this, as the next time it was showing empty, I was able to siphon over 5 gallons out of the tank.   Im sure my siphon couldnt get it all...so it takes at least 5-7 gallons in the tank.   I suppose i could bend the arm more, but, if i do that then it would show full for a much longer period of time.   

I.e.   Their very inaccurate .

So, be it!!