Bouncing/nonresponsive fuel gauge MEP-803A

[Light in the Dark]

Any initial thoughts on where to start the hunt? The unit is about 50% full right now. The needle is below E, but does bounce up and down slightly as the unit is running.

 

[Haoleb]

Just had a similar issue with mine that I found to be the fuel gauge itself and not the sender. There is a section of the TM that talks about testing the gauge with the voltage adjust pot used for variable resistance or you can use plain ole' resistors to see if the gauge responds correctly. IIRC, it should be around 36 ohms resistance from the sender wire to ground when the tank is full but I'd have to check to be sure.

EDIT. TM says that sender should be 216-264 ohms for empty and 29-36 for full. So resistance will go up as fuel level drops.

In my case the gauge would read correct for a couple seconds when I first started it up then would go way down below E and it did this with no repeat-ability. I did some testing and replaced the gauge and it works perfect since.

 

[Light in the Dark]

Thanks for the TM info. I see its a sheet metal off affair.... maybe this weekend I can get to it. Like everything else, never enough time. I have a potential buyer for this unit, and I don't want to deliver something that isn't 100% on point. Thanks again.

 

[Haoleb]

You shouldn't have to take any sheet metal off unless you find that the sender is the problem. Just need to get out a multimeter and a couple of jumper wires and do some jumpering on the drop down control panel. I have a resistor decade set so I did not do it the way the TM describes but its pretty simple to see where your problem is.

 

[Light in the Dark]

You shouldn't have to take any sheet metal off unless you find that the sender is the problem. Just need to get out a multimeter and a couple of jumper wires and do some jumpering on the drop down control panel. I have a resistor decade set so I did not do it the way the TM describes but its pretty simple to see where your problem is.

Yeah the TM of course calls out testing the sending unit first. Should I be able to test with my multi-meter at the back of the gauge alone?

 

[Haoleb]

Yeah the TM of course calls out testing the sending unit first. Should I be able to test with my multi-meter at the back of the gauge alone?

You would be able to estimate if it is reading approximate to what it should be. But if you test the gauge and it works fine then that basically narrows it down to the sender or a wiring issue.

 

[Light in the Dark]

I'll need to break out the book again for this... didn't jot down notes from when I first posted this about how I was going to test the gauge alone first. How are you using these jumper cables? I would have assumed if its reading resistance, my regular multimeter would pick up what I need.

 

[Haoleb]

In the TM the describe using the voltage adjustment pot as a source of variable resistance to test the gauge with. Its too detailed to describe here but the TM lays out everything you need to know.