Referencing some other important info I found regarding the fuel sending unit and rated ohm resistance and difference between empty and full as well as how the fuel calculation system works for these cars, a friend and I came up with an idea for a simple ohm signal repeater, probably Raspberry PI or other similar DIY-friendly board/system.
Basically, the computer takes the two stated ohm ratings, averages or combines them (some literature conflicts on what it actually does), then uses that to calculate how much fuel is left. As another poster stated, simply unplugging the bad fuel sending unit will make the gauge drop to zero, most likely due to it either reading zero ohms or infinite ohms (and if I get something wrong here, feel free to correct me, I’m basing this on a convo with another friend about it, I’m not that knowledgeable when it comes to electrical work).
Now, how the solution might work is taking a board, tapping into the working fuel sending unit, letting that main signal pass through, but then having the board duplicate the same ohm load, then feeding back into the wires that are joined to give the total ohm reading of giving the computer something to work off of, with in the 5-332.5 ohms of the combined ohm load needed to determine fuel.
I believe this will work because based on the post linked above’s research, the ejector (driver’s side jet pump that balances the right tank) only works off of flow dynamics and is not powered, only the level sender. That ejector has a rating for 2.5-7.5 ohms for full, and 165-170 ohms for empty. The fuel pump sending unit has a rating of 2.5-7.5 ohms for full and a rating of 157.5-162.5 ohms for empty. These added together gives up the fuel level sensor ohm rating of 5-15 ohms for full and 322.5-332.5 ohms for empty.
So let’s set up the scenario. Ejector level sender disconnected, spliced into with repeater. Repeater spliced into working level sender. Fuel pump sending unit reads 82.5 ohms, approximately half of a tank. Now, on a half tank with a working ejector sending unit, we would get approx. 86.25 ohms. this combined, gives us 168.75 ohms, or just shy of over half full based on how the computer calculates it. Now if we duplicated the 82.5 ohms, we would get a combined total of 165 ohms. which is a difference of 3.75 ohms, or about 2.27. If we were to translate this into a difference of fuel, with a total capacity of AWD cars of 18.5 gallons, the difference works out to about 0.23 gallons of gas, I think well within a margin of error for the average driver.
If I’ve missed anything or you have questions, I will try to answer everything below.