Yet another fuel gauge problem
April 28th, 2018, 06:12 PM
#1
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Join Date: Feb 2014
Posts: 4
Yet another fuel gauge problem
I have a 1970 rally gauge in a 70 Cutlass 442 clone, a Tanks Inc fuel tank with electric fuel pump in tank (used to have EFI, but went back to carb last year-still using the electric fuel pump). The Tanks inc tank was installed 3 years ago and no problems with the gauge until this year. Car is a daily driver for the last 31 years.
Problem-at the beginning of the year, fuel gauge starting jerking around like an EKG, jumping 1/8 to 3/8 of a tank back and forth in a second or less.
Have tried to read all of the threads on this topic and here is what I have done so far:
I am on my fourth sender, three standard style and the last one is the floatless style. That was done by a speed shop. The gauge still jerks around with each sender. Problem is worse now after all these senders than when started with the original one-that one fluctuated around the true reading. Now it reads close to 1/2 tank too high when not jerking around.
I have done the following tests suggested by Jaunty75, Oldscutlass and others:
1. Disconnect sender wire at trunk. Gauge goes over F.
2. Ground sender to gauge wire . Gauge goes right to E.
3. Tested ohms from sender at the harness, and after that, with a separate bypass wire from the sender connection in the trunk-get the same reading.
a. The ohm reading is stable with the car resting.
b. However, once I start driving the ohm readings fluctuate, whether using the tan wire pin in the gauge connector as the source , or when using a separate wire running from the sender connection at the trunk to the multi meter.
4. I have jiggled the wired from the sender to the trunk and the ohm reading at rest did not fluctuate.
5. The sender ground connection is fresh with all of the replacement senders recently installed. I moved the ground to another spot with a previously drilled and unused hole. No difference.
It seems the gauge is accurately reflecting the sharply changing ohm readings measured when driving.
It also seems the wire from the sender connection in the trunk to the gauge is good, as I get the same readings using a separate wire.
When connected to the dash, the gauge is reading quite high, about 3/8 to 1/2 tank too high. When I remove the gauge from the dash and the in dash ground(but still fully connected to the harness) , the reading drops quite a bit, possibly close to an accurate reading.
I have driven the car with the gauge in my hand and though the readings are lower, the gauge needle still jerks around, 1/4 tank at time (sometimes more, sometimes less, but averaging a 1/4 tank) both up and down, several times within a second or two. It does not jerk all the time but probably 50% of the time in city driving. On the highway the other day with the gauge connected and in the dash, it was much more stable though way too high, until I exited- it jerked around quite a bit from the exit ramp to just crossing over the freeway, varying up to 3/4 of a tank!
I have also driven the car with a separate wire coming from the sender connection in the trunk to the multimeter, same result, large fluctuations in the ohm readings. Just driving around to the next street and back (4/10ths of a mile), ohm readings ranged from 34, 44, 57 up to the seventies and all points in between.
Seems that the gauge acts up when the gas is moving around in the tank. No idea why, but maybe the smart people on here can explain.
Hopefully someone here can suggest something else to consider as the source of the violently fluctuating readings coming from four different senders.
Any thoughts will be greatly appreciated!
Problem-at the beginning of the year, fuel gauge starting jerking around like an EKG, jumping 1/8 to 3/8 of a tank back and forth in a second or less.
Have tried to read all of the threads on this topic and here is what I have done so far:
I am on my fourth sender, three standard style and the last one is the floatless style. That was done by a speed shop. The gauge still jerks around with each sender. Problem is worse now after all these senders than when started with the original one-that one fluctuated around the true reading. Now it reads close to 1/2 tank too high when not jerking around.
I have done the following tests suggested by Jaunty75, Oldscutlass and others:
1. Disconnect sender wire at trunk. Gauge goes over F.
2. Ground sender to gauge wire . Gauge goes right to E.
3. Tested ohms from sender at the harness, and after that, with a separate bypass wire from the sender connection in the trunk-get the same reading.
a. The ohm reading is stable with the car resting.
b. However, once I start driving the ohm readings fluctuate, whether using the tan wire pin in the gauge connector as the source , or when using a separate wire running from the sender connection at the trunk to the multi meter.
4. I have jiggled the wired from the sender to the trunk and the ohm reading at rest did not fluctuate.
5. The sender ground connection is fresh with all of the replacement senders recently installed. I moved the ground to another spot with a previously drilled and unused hole. No difference.
It seems the gauge is accurately reflecting the sharply changing ohm readings measured when driving.
It also seems the wire from the sender connection in the trunk to the gauge is good, as I get the same readings using a separate wire.
When connected to the dash, the gauge is reading quite high, about 3/8 to 1/2 tank too high. When I remove the gauge from the dash and the in dash ground(but still fully connected to the harness) , the reading drops quite a bit, possibly close to an accurate reading.
I have driven the car with the gauge in my hand and though the readings are lower, the gauge needle still jerks around, 1/4 tank at time (sometimes more, sometimes less, but averaging a 1/4 tank) both up and down, several times within a second or two. It does not jerk all the time but probably 50% of the time in city driving. On the highway the other day with the gauge connected and in the dash, it was much more stable though way too high, until I exited- it jerked around quite a bit from the exit ramp to just crossing over the freeway, varying up to 3/4 of a tank!
I have also driven the car with a separate wire coming from the sender connection in the trunk to the multimeter, same result, large fluctuations in the ohm readings. Just driving around to the next street and back (4/10ths of a mile), ohm readings ranged from 34, 44, 57 up to the seventies and all points in between.
Seems that the gauge acts up when the gas is moving around in the tank. No idea why, but maybe the smart people on here can explain.
Hopefully someone here can suggest something else to consider as the source of the violently fluctuating readings coming from four different senders.
Any thoughts will be greatly appreciated!
April 28th, 2018, 06:48 PM
#2
Administrator
Join Date: Oct 2009
Location: Poteau, Ok
Posts: 40,556
There is a resister on the back of your gauge. Investigate this:
http://www.chevyclassicsclub.com/the...ry-1965-newer/
http://www.chevyclassicsclub.com/the...ry-1965-newer/
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