Another Fuel Gauge question...

[SR2dude]

I am trying to fix the fuel gauge on my 800 and I am running into some problems. When I test the gauge itself, my tester light blinks. And then I take it back to the wire on the gas tank and it also blinks. Is it supposed ot blink? If its not, any idea on what to do?

Thanks and happy fathers day!

 

[Michael Mayben]

Do a search using keyword "constant voltage regulator" in the electrical sub-forum. That should bring up several threads regarding how the instruments are powered on IH light line vehicles, including the s800.

You are trying to read a nominal 5vdc reference signal with a test light or a dvom and that is not possible. The constant voltage regulator is the power supply for all the instruments except the ammeter and is not a solid-state item but an old skool vibrator-type power supply. It "down-converts" b+ to a +5vdc reference voltage.

Do not attempt to feed b+ to the instruments, they will go up in smoke immediately.

 

[Eric VanBuren]

Yes it is supposed to blink, so that is a good thing. Your test has verified that the cvr is performing it's basic function of switching b+ on and off in an attempt to produce an average voltage of ~5v. That does not however mean that it is working withing calibration. You've also verified the gauge's heater element and wiring to the tank are still intact. Again that doesn't mean that the gauge is properly calibrated and the wiring doesn't have any excess resistance. All in all though that test proves that the basic system is intact and "working" up to the fuel sender.

It also points to the sender or it's lack of a proper ground as the most likely cause, if Your gauge is totally in-op. If your gauge just reads low then excess system resistance or an out of calibration cvr or gauge could be the problem.

The sender should have a resistance of 10 ohms when full and 73 when empty.

 

[Michael Mayben]

yes it is supposed to blink, so that is a good thing. Your test has verified that the cvr is performing it's basic function of switching b+ on and off in an attempt to produce an average voltage of ~5v. That does not however mean that it is working withing calibration. You've also verified the gauge's heater element and wiring to the tank are still intact. Again that doesn't mean that the gauge is properly calibrated and the wiring doesn't have any excess resistance. All in all though that test proves that the basic system is intact and "working" up to the fuel sender.

It also points to the sender or it's lack of a proper ground as the most likely cause, if Your gauge is totally in-op. If your gauge just reads low then excess system resistance or an out of calibration cvr or gauge could be the problem.

The sender should have a resistance of 10 ohms when full and 73 when empty.

The "10>73ohm" callout is perfect world. In the real world that callout is +/- 20% and still provides proper functionality.