740 gas gauge inaccurate
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740 gas gauge inaccurate
I was driving on the highway with 3/4 tank (which is correct) and then it started to go down very quickly until it was at just above empty, at which point I pulled over to check for leaks, there weren't any. I kept driving and the gas gauge went back up to about a quarter tank and then back down to empty. Any idea what this could mean? It's a 1990 740 GL. Thank you.
no mo volvo
Joined: Oct 2010
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From: 37 North on the left coast
either its the sending unit which is in the gas tank, accessible from the floor of the trunk just behind the back seat, or its the wire from that sending unit to the instrument panel gas gauge.
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I don't think Its the sending unit, because it showed at least something for a while and then it went back to empty again. I'll check the wiring.
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no mo volvo
Joined: Oct 2010
Posts: 11,289
Likes: 109
From: 37 North on the left coast
the sending unit is a mechanical float driving a contact against a variable resistor, it quite easily can go erratic.
one of the commonest places for the wire to fail is where it goes through the cover plate into the gas tank. I'm not 100% sure, but I think the wire goes up the left side of the car below the doors and under the door sills where the main harnesses are.
ok, I don't have 1990 wiring diagrams, but on a 1991 740/940, the signal is a grey-white wire, and the ground is a brown wire, they go through 2 bulkhead connectors, "C" is a few pin connector near the top of the left rear wheel hump, grey-white is on pin 2, and brown is on pin 3, then connector B is a big rectangular lotsa-pins bulkhead connector on the left side of the firewall near the A pillar (forward of the front door), where grey-white is pin 9, and brown is pin 16. the signals go into the back of te instrument panel on the larger straight line connector, grey-white on pin 18/3 and brown on pin 18/4... the ground signal goes through the instrument panel, is connected to the ground bus in the fuse panel which in turn is grounded on the RIGHT A pillar ground block near the floor and just below the lower front right door hinge..
one of the commonest places for the wire to fail is where it goes through the cover plate into the gas tank. I'm not 100% sure, but I think the wire goes up the left side of the car below the doors and under the door sills where the main harnesses are.
ok, I don't have 1990 wiring diagrams, but on a 1991 740/940, the signal is a grey-white wire, and the ground is a brown wire, they go through 2 bulkhead connectors, "C" is a few pin connector near the top of the left rear wheel hump, grey-white is on pin 2, and brown is on pin 3, then connector B is a big rectangular lotsa-pins bulkhead connector on the left side of the firewall near the A pillar (forward of the front door), where grey-white is pin 9, and brown is pin 16. the signals go into the back of te instrument panel on the larger straight line connector, grey-white on pin 18/3 and brown on pin 18/4... the ground signal goes through the instrument panel, is connected to the ground bus in the fuse panel which in turn is grounded on the RIGHT A pillar ground block near the floor and just below the lower front right door hinge..
Thread Starter
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Member
Joined: Oct 2019
Posts: 88
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the sending unit is a mechanical float driving a contact against a variable resistor, it quite easily can go erratic.
one of the commonest places for the wire to fail is where it goes through the cover plate into the gas tank. I'm not 100% sure, but I think the wire goes up the left side of the car below the doors and under the door sills where the main harnesses are.
ok, I don't have 1990 wiring diagrams, but on a 1991 740/940, the signal is a grey-white wire, and the ground is a brown wire, they go through 2 bulkhead connectors, "C" is a few pin connector near the top of the left rear wheel hump, grey-white is on pin 2, and brown is on pin 3, then connector B is a big rectangular lotsa-pins bulkhead connector on the left side of the firewall near the A pillar (forward of the front door), where grey-white is pin 9, and brown is pin 16. the signals go into the back of te instrument panel on the larger straight line connector, grey-white on pin 18/3 and brown on pin 18/4... the ground signal goes through the instrument panel, is connected to the ground bus in the fuse panel which in turn is grounded on the RIGHT A pillar ground block near the floor and just below the lower front right door hinge..
one of the commonest places for the wire to fail is where it goes through the cover plate into the gas tank. I'm not 100% sure, but I think the wire goes up the left side of the car below the doors and under the door sills where the main harnesses are.
ok, I don't have 1990 wiring diagrams, but on a 1991 740/940, the signal is a grey-white wire, and the ground is a brown wire, they go through 2 bulkhead connectors, "C" is a few pin connector near the top of the left rear wheel hump, grey-white is on pin 2, and brown is on pin 3, then connector B is a big rectangular lotsa-pins bulkhead connector on the left side of the firewall near the A pillar (forward of the front door), where grey-white is pin 9, and brown is pin 16. the signals go into the back of te instrument panel on the larger straight line connector, grey-white on pin 18/3 and brown on pin 18/4... the ground signal goes through the instrument panel, is connected to the ground bus in the fuse panel which in turn is grounded on the RIGHT A pillar ground block near the floor and just below the lower front right door hinge..
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