98 V70XC replaced fuel pump, now gauge not working.

[Ludermilch]

What I thought would be a simple replacement of a fuel pump has now become something more. I just put in a pump to replace one that was
that repaired sometime last year. That old pump only had the pump wires connected and not the level sender. I was hoping the new complete pump would not only provide a leakproof seal but also give me an idea how much fuel was in the tank.

I have looked and not found a solution to my delema. What steps do I need to take to track down the problem?

Any links or advice would be greatly appreciated.

[jose456891]

I had fuel gage problems not too long ago, this is what I did:


From: https://www.matthewsvolvosite.com/forums ... =1&t=61820

The likely cause of incorrect fuel gage reading is the sender unit in the tank (float) is gummed up or stuck. I had the unfortunate fortune of burning the fuel gage on the dash by probing and applying battery voltage to the wrong wire.

Here is a link to my encounters with the fuel reporting system on my 850:
viewtopic.php?f=1&t=59470

The following is based on a 1996 850 Wagon GLT, it should be aplicable exactly the same on V70's.

This is what you need in order to test the Dashboard Fuel Gage, and Sender Unit:

10mm Socket + Wrench
DVOM with ability to measure Ohms in the range of 0 to 1000 ohms
1x 500 Ohm potentiometer (variable resistor) available at RadioShack
1x Pair of small aligator jumper cables (the small ones for small circuits, available at RadioShack)

The way the fuel resorting system works is by feeding 7 volts to the sender unit (float). The sender unit is a big potentiometer that changes its resistance according to the fuel level in the tank. There is a physical float that actually floats on fuel. This drives a small arm connected to a connector surface with different resistance values.

This is the specified resistance range according to Volvo: 7.5-12.5 to 322.5-327.5 ohms. The input voltage to sender unit is specified at 7 volts.

Go to the trunk, remove the lining and locate a connector with a YLW/RED and BLK wires. This is the wire responsible for reporting fuel level.


Test for shorts of the power feeding the sender unit:

1) Disconnect the connector
2) Probe the YLW/RED and ground with DVOM. YLW/RED to (+) probe, bare metal pice on car black jumper cable to (-) probe on DVOM.
3) Voltage should be close to 7 DC Volts when ignition is on. If no voltage check for open circuit on YLW/RED or short to ground.
4) Probe BLK wire and ground for continuity. Bare metal on car to black jumper cable to (-) probe on DVOM. BLK wire to (+) probe on DVOM. The resistance should be 3 to 0 ohms. If resistance is infinite or very high, look for damaged BLK wire or open circuit.

Test Dashboard

1) Disconnect connector, do all tests on the connector feeding into the car. Make sure ignition is off.
2) You will construct a ,parallel circuit with the potentiometer, DVOM and car's connector.
3) Stick (+) DVOM probe to YLW/RED conector. Stick (-) DVOM probe to BLK conector. Turn DVOM to ohm scale.
4) Grab a pair of jumper alligator cables.
5) Clip (+) alligator jumper cable between (+) DVOM probe and (+) side of potentiometer.
6) Clip (-) alligator jumper cable between (-) DVOM probe and (-) side of potentiometer.
7) Dial potentiometer to 10 ohms. Use DVOM to pinpoint the 10 ohms.
8 ) Turn ignition on. The fuel gage should read full.
9) Slowly dial potentiometer to 170 ohms. Tank should read 1/2 full.
10) Slowly dial potentiometer to 325 ohms. Tank should read empty. *
11) If fuel gage reads something else other than above, replace cluster.

* it's OK to go past 320 ohms with potentiometer. This will reduce the voltage sent to the cluster down to zero, which its safe. It will probably trigger a check engine light on V70s, on my 850 nothing was set.

Test Sender Unit:

1) Connect DVOM probes to float and set to Ohms. (+) Lead to one wire, (-) to the other, polarity does not matter. If the resistance is not within 7.5-12.5 to 322.5-327.5 ohms, replace/clean sender unit (float).
2) Remove sender unit. Connect to DVOM to sender unit as in step #1. Physically move float up and down, resistance should vary, if not replace float.
3) Set float to position were fuel is highest. Ohms should read 7.5 to 12.5. If incorrect replace sender unit.
4) Set float to position where fuel is lowest. Ohms should read 322.5 to 327.5 Ohms. If incorrect replace sender unit.
5) Slowly move the float arm up and down. Resistance should vary within 7.5-12.5 to 322.5-327.5 Ohms. If there are jumps, drop offs or the Ohm value is stuck for any period of time, your sender unit is dirty. Replace or clean sender unit.

If cleaning sender unit, use kerosene or mineral spirits.


Here is a link to Volvo's own instructions. I like mine better because they are more thorough and applies to 850 and v70's 1993-2000's. No need for special computer equipment.

https://www.dropbox.com/s/5wijz7sll03zf ... 0panel.pdf

[jose456891]

OP: Did you sort the problem out?

[Ludermilch]

I have not had a free moment to really explore the solutions provided. Funny that today is when I planned to do so.
Thank you for asking. Will report soon.

[Ludermilch]

Finally made time to work on the Guage and find out what the problem was. While checking the wires, found a severed wire. After reconnecting the wire my Guage started working again. Went to fill up the tank and the fuel level guage only reports half a tank. Now I need to figure out what that cause is.

[holler1]

Ludermilch, my understanding is that the AWD (which i have) and the XC have two sending units, on right and left sides of the tank, connected in series. My guess is that one of your sending units has a short, so the total resistance the system sees is 1/2 what it should be. I have one sender that is open, so mine sees infinite resistance, and shows 0 on the gauge. I added a resistor in place of the bad sender, so it shows full OK but reads 1/2 full when the tank is empty. I suggest you
look for the electrical diagrams for the XC and check resistance for each sender.