So this week I swapped a LM7 5.3 ls and a 4l60e into my 1990 240 wagon. I removed the complete engine wiring harness and the associated computers. This also removed part of the fuel pump wiring, no big deal since the new pump is run off its own relay on the LS harness. My problem that the fuel gauge was also part of this circuit. I assumed that I could just tap into the grey wire coming from the sending unit and hook it to the back of the gauge bypassing everything, but that is not the case. It seems like the gauge is looking for a ground and the sending unit is putting off positive voltage? Does anyone have any idea how to connect the sending unit to the gauge?

Thanks

 

the sending unit is a variable resistor, it doesn't output any voltage. The gauge circuit provides some voltage and measures the current to tell what the resistance is....

I think you need a ground wire connected to the sender back at the gas tank, however... thats the brown wire, and was shared with the ground for the intank fuel pump...


edit: is your fuel pump in the tank, or under the car? and, did you remove the intank pump, or are you just sucking fuel through it with your LS fuel pump ?

 

I replaced the in tank pump with a walbro in tank and removed the main volvo pump, then just ran AN line all the way up. I kept the ground coming out of the in tank pump, it was just screwed into the sheet metal. The black wire is run from the new fuel pump relay, and the grey i tried running straight to the gauge.

 

disconnect the pump and and sender at he top of the tank, and use a multimeter in 'ohms' mode to see if there's resistance from the grey to brown wire. i can't see from that picture how the brown/ground wire is connected to the assembly, does it just go to the metal frame? how is the black wire from your pump connected to the ground ?

 

So there is no continuity between the grey and brown wire at the tank, I assume thats somehow the issue. Any idea what that connection should look like in the tank? The gauge worked before I did the swap, but I may have broken something inside during.

 

the brown wire should go both to the 'ground' or whatever on the sender, and to the black wire on the fuel pump. If the sender has two wires coming from it, the one thats not connected to the grey would be the ground.

ok, one more test. see if there's resistance from the grey wire to the metal plate on top... and that the brown wire is NOT connected to said metal plate.
if there's resistance from grey to the metal, then the brown wire should be somehow connected to the metal inside.

 

So there is no continuity between the grey wire and the top metal plate.

 

then I'm afraid you're going to have to pull it out again and figure out where the ground is for the fuel level sensor and get it connected to the brown ground wire. while its out, if you have an ohm meter hooked across the fuel level sensor, the resistance should change when you move the float up/down...

 

Makes sense, thanks for the help!

 

It's probably broken at the hermetic seal on the sending unit. Common for these cars. Probably was ok but flexing the wire when pulling the sending unit out probably jarred it and it no longer has continuity through to the sender. Pull the sending unit out and ohm it out through the wire down to the sensor. If it doesn't have continuity, the only solution is a replacement sending unit.

 

true, it could be the grey wire thats broken.... the fuel pump wire and ground have continuity to the fuel pump.