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Old 11-14-2017, 09:11 AM   #1
Wesdunns70t5m
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Default 1990 760 sending unit help

Hey there everybody, hope alls well. I seem to have screwed something up this past weekend, and am turning here for some help.

My 760 turbo with lh2.4 had an extremely noisy main pump, and extremely quiet pre pump. This past weekend I changed the fuel filter (definitely needed) and my in tank pump. I opted for a genuine walbro, which has checked out visually and audibly. I also ordered a fuel pump relay kit, which runs the fuel pump off of battery voltage, with an in-line 30amp fuse and relay. Iíve got that installed as well without any problems. My problem is with the sending unit.

How I ran the new wires for the fuel pump is like this: I cut the black wire that attached the in tank fuel pump to a solder underneath the sending unit metal face (inside the tank). I also cut the red wire outside of the fuel tank, and pulled the wire through the same faceplate, and removed the attached red wire when the pump came out.

Iím not sure if cutting that red wire is what did it, or maybe I got the float hung up on something when I was reinstalling everything, but now my gauge reads empty, and the yellow empty light is illuminated. My gauge was working perfectly fine before this, and seeing as my speedo/odometer doesnít work, Iíll just be estimating when I need gas. Any help would be appreciated, and Iíd hate to screw something up more.

I was thinking I might need to solder the cut red wire to the new fuel pump power wire, but Iím not fully learned in electronics and donít want my learning curve near a fuel tank
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Old 11-14-2017, 11:23 AM   #2
EivlEvo
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I'm confused as to why you did all of this in the first place?

My knowledge is on the 240 only. If the gauge is reading zero though I believe it's either hung up, or not receiving power. If you lose your ground it will typically just read full. But some of the wiring geniuses will need to chime in on this.
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Old 11-14-2017, 12:08 PM   #3
lummert
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Did cutting the black wire defeat the fuel level sending unit wiring circuit?
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Old 11-14-2017, 12:29 PM   #4
Wesdunns70t5m
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Whining main fuel pump, and no noise from the fuel tank with ignition on.. I know the filter needed changing, so that may have been what was needed to quiet the main pump, but I do plan on upgrading this car, so I figured I’d start with a fuel pump. No gains now, just giving myself more headroom is all.

And I don’t believe cutting the black wore did it. I just cut the black wire, and soldered it to the new fuel pumps wire. That wire just attaches the pump, to the underside of the metal face. The red wire that I cut, went through the face and went to the connector by the wheel well. Does the power wire for the pump also power the sending unit? If so, than I really think I just need to tap the red wire (old fuel pump power) into the new fuel pump power wire.
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Old 11-15-2017, 03:05 PM   #5
Wesdunns70t5m
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Bump it up. I’m waiting until the weekend to tear into the tank again, hoping to get an answer before then
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Old 11-15-2017, 03:34 PM   #6
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I'm thinking that the cut wire was also the gauge sending unit ground.
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Old 11-15-2017, 05:27 PM   #7
Wesdunns70t5m
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So after my last comment I filled the car up with gas. As soon as I started it the gas gauge went to 1/2 full, than as I drove 500 yards or so it rose to 3/4 full. At this point I’m assuming either I didn’t install it correctly, or the sending unit crapped out from being handled after so long
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Old 11-15-2017, 08:53 PM   #8
lummert
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Think there is a write up somewhere on repairing this type sending unit.

http://www.volvoclub.org.uk/faq/Elec...augeFluctuates

Last edited by lummert; 11-15-2017 at 09:01 PM..
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Old 11-16-2017, 08:00 AM   #9
Wesdunns70t5m
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Ahhhh now that’s the ticket. Somehow I didn’t come across that page, thank you. I’ll post back this weekend with some updates
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Old 11-18-2017, 05:07 PM   #10
Wesdunns70t5m
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So I tore into it today and found that my sending unit was installed incorrectly. The bottom of the unit was facing towards the passenger side instead of straight down. I’ll be filling it up tonight and paying attention, but I’m pretty sure my problem is fixed.
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