| Author | Message | ||
| Ron Leiferman (Ron_In_Sd) (12.111.217.5)
Rating: |
I have a fuel gauge and a low fual light. I know that the gauge does not work. I am not sure about the light. I want to figure out if the sending unit is bad or the gauge. Does anyone have a simple test to test the sending unit and also the gauge? This is in a 24 v Prevost LeMirage XL | ||
| TWO DOGS (65.179.192.127) Rating: N/A |
set simpson to 'ohlms'...move float arm up & down....should make a difference on the scale....if it does..then it's 'probably the recieving unit...might be spelling it wrong...it's the little horseshoe thingy .. | ||
| Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A |
Use a broom handle to dip the tank. You can even cut knotches on it to get an accurate reading. My gage acts funny at times too. Good luck. | ||
| Tim Jones (Torquester) (12.72.177.64)
Rating: N/A |
Hi Ron, I'd agree with Two Dogs. The fuel level sending unit is usually a variable resistor. As the height of the fuel in the tank changes the float moves up or down. This moves a "wiper" across a coil of wires producing variable amounts of resistance. The resistance can be measured with any decent multimeter set to read ohms. The sending unit must be isolated from the rest of the circuit. I have seen sending units that show an open circuit somewhere in the middle of their travel range, yet are still a continuous circuit through the remaining range. SO.........check the sending unit for a linear change (resistance or voltage) through its operating range. Check for a voltage signal (in)to one terminal on the sending unit. There should also be a voltage out signal on the other terminal at the sending unit. Follow that signal to the gauge and make sure that it is the same as it was at the sending unit. If all checks well an you have an excellent ground for the gauge.....go get a new gauge. HTH, Tim | ||
| ChuckMC9 (Chucks) (66.167.165.236)
Rating: N/A |
Here's something Brian wrote back in December, it was very helpful to me: (and thanks again, Brian!) ----------------- Chuck, most fuel senders work by varying the resistance to ground. With the "key" on or the engine running and the wire to the sender off, run a jumper wire from ground to it. The gauge should peg to FULL. If it doesn't peg full the gauge is bad or the wire from the sender is. To test the gauge involves access to the back of the gauge. With the key on, use a meter and determine which terminal post has power to the gauge, the opposite post should go to the sender, with a jumper wire ground that terminal, if the gauge pegs the needle to full, the gauge is good, the wire to the sender is bad. If the gauge doesn't move, the gauge is bad. If the gauge and wire test good, test the sender, To test the sender make certain the level of the fuel is below the sender. Unscrew the sender with the wire off, carefully remove it and the float (you may have to rotate the sender)to remove it. Reattach the sender wire, clip your jumper wire from ground to the rim of the sender, with the key on, and someone looking at the gauge, move the float arm through its full arc, if the gauge does not move, the sender is bad. If at some point in the arc the gauge needle drops and does not move until you raise the arm again, the sender is bad. I hope that helps Brian PS: Turned out the wire's connector to the tank was covered with crud - a thorough cleaning fixed it right up! (I *think*, because I can't afford to fill up the tank these days!  | ||
| Phil Dumpster (24.16.243.37) Rating: N/A |
99% of fuel gauge problems involve the wires connecting the sender and the gauge, and the connections involved. While sender and gauges can and do fail, it is less common than you think. Troubleshoot the wiring first before messing with the components. | ||
| Stephen Fessenden (Sffess) (65.130.8.165)
Rating: N/A |
The test of a fuel gauge by grounding is supposed to be a momentary contact unless the book says longer is OK. The gauge may not be able to handle 0 Ohms for too long. Full may not be zero ohms but a very low value like 5 or 10 ohms. Use a momentary grounding unless you are sure. | ||
| BrianMCI96A3 (65.40.247.63) Rating: N/A |
In my 25 years of experience as a diesel mechanic, I have found that the sender is the culprit in the vast majority of cases. Over the years I have had to replace very few fuel gauges, and likewise experienced few wiring problems. Corrosion on terminals occasionally creates problems, but even that still is a distant second to sender failures. Generally, the gauges I have been associated with on heavy trucks and buses have no difficulty handling direct grounding for several seconds, long enough at least to go from the tank to the cockpit and back. Brian | ||
| Ron Leiferman (Ron_In_Sd) (12.111.217.5)
Rating: N/A |
Thanks for the information. This way I can test to see if is is the sender or the gauge. |
