98 V70XC Fuel Gauge Hack

[Ludermilch]

So here I have this new, self caused, problem with my fuel gauge. Here is a quick recap of how I got here.
Bought the XC with a bad fuel pump. Replaced that. Wiring was all goofy. Fixed that but it only measured as half full. Could also only get only 200 miles out of a full tank. Today I dropped the rear suspension and tank to get at and replace a leaking quick disconnect and fuel line. Also pulled this... The LH fuel "pump" and float assembly. It was pretty much falling apart. While cleaning it the wiring for the float disintegrated and now my gas gauge isn't working the same. Bonus: I now have fuel "pumping" from the LH tank!

What happened now is my gas gauge now measures empty if I leave it disconnected, or it measures as half full on an empty tank if I connect the wires.

Can I.... And I am going to experiment, somehow connect the LH wires to the RH so at least get the gauge to show me when it is truly empty?
I have read where a forum member put in a resistor to correct for a gauge not reading correctly. I think it was a C70

[Ludermilch]

Update : Because the wiring on the sender fell apart, there was no current going through the wiring, meaning that the gauge showed an empty tank. When I cut and connected the wires the resistance on the 7 volts going through the gauge was higher than designed and showed half a tank(even though it was actually empty).

The solution was add a few resistors to act like the LH sender was showing empty and if the RH sender was also empty then the fuel gauge would show the true level of the gasoline. Down side is that when I fill up the tank the fuel gauge, it will only register one side of the tank and show only half full. Still a positive now I can really tell when the car is low.

Started with a 330 ohm and that was too much. That just showed empty. Now I'm at 141ohm and it shows what I think is in the tank. I will see how it goes..

[DrJammer]

So I am a victim of this issue myself. Recently had a fuel pump replaced by a non-volvo mechanic. Had to take it back for a fuel leak shortly after, and now my gauge is not reading properly. I remember my indy volvo guy quoting me more as he would replace the sender in the other tank as well.

So it appears one sender is wrong. I read a few forums, and am not sure about resistors etc., but I'd like to know if I can workaround this without using my handwritten 'gas log'.

If I fill the tank up, will I be able to use the whole tank or does this fault mean I only can burn from one side of the tank? Is there any way to address this issue without dropping the tank again? I can live with this issue if I keep diligent mileage and fuel records I suppose. I assume a bottle of techron won't fix this?

[Ludermilch]

Apologies for the late reply. Let's break it down into the separate parts.

Because the AWD models had a saddle tank, the car uses two pumps and two senders. The senders work in series. If one fails it affects the other. If one sender has broken components, such as a wire, your gauge will read empty because it is not getting a signal from the senders. If one sender is stuck, perhaps on its lowest point, then your gauge will only read as half full even if you fill it up.

The pumps are also in a type of series. Kinda like a split loop. The passenger side of the tank has the electric pump that powers the whole system. The driver side of the tank contains an "evacuation pump" that uses pressure from the electric pump to siphon fuel from the driver side and pump it into the passenger side.

If you are getting around 300+ miles to a full tank, both pumps are working right.

If you are not getting a reading on your fuel gauge then you have a short on one of the senders or wiring.

If you have half a tank or more showing on your gauge, one of the senders is stuck.

Techron could work if the sender is gummed up.

I can detail out a solution for you if you want.