Fuel gauge pegged

[homelessduck]

The fsv seems to work , when I switch tanks the gauge reacts , but they are both pegged past full. Any ideas before I drop the tanks?

 

[madpogue]

What year truck? If it's a OBS, here's the diagram - http://userpages.chorus.net/elephant/FuelTankSelector.pdf . Most likely it's NOT in either tank, but a break in the wire between the FSV and the gauge head. Open circuit == infinite resistance == gauge pegs past full.

 

[homelessduck]

It's an 88. Thanks!

 

[madpogue]

Well the wire colors MIGHT be different with a brick, but the concept is the same. High resistance = full peg.

(As an aside, it would be the opposite with a slantnose '83-'86, as the level-resistance relationship is reversed.)

 

[Thewespaul]

Make sure it’s not unplugged or loose at the sender

 

[madpogue]

^^^^ That would have to happen on both senders. That's why it's more likely forward of the FSV.

 

[towcat]

if you have spare parts on hand, plug in the spares one at a time, so you can avoid opening up the tank. the FSV is possibly a bear to get to though. bottom line, your problem is in one of three areas. one) the sender. two) the FSV and three) the wiring. having a volt/ohm meter will be invaluable for this diagnosis run.

 

[homelessduck]

I checked out the connections at the tanks and fsv. I traced the wires from the fsv, didn't see any breaks in the wires. Could it be the gauge itself?

 

[Macrobb]

Check it with an ohm-meter?

 

[homelessduck]

I'm an idiot when it comes to electrical lol. How would I go about doing that?

EDIT: I screwed around with it for a minute and figured out how to do it. Lol

 

[homelessduck]

Ok , so I did some testing today. I swapped gauges, no change. If I short the fuel sender plug it makes the gauge go to empty. I ohm tested the sender while it was unplugged and nothing happened on the meter. Bad sender?

 

[madpogue]

What do you mean by "nothing happened"? How exactly did you connect the meter? What resistance range did you set it to?

Did you continuity / ohm check the wire from the FSV to the gauge head?

 

[Macrobb]

Well, if he shorted the connector at the tank and it worked, the wiring/gauge is good. Pull the sender and look at/replace it.

 

[homelessduck]

With it set to 200 or 2k ohm , can't remember , I touched the two leads coming out of the sender. The meter didn't read anything. I then shorted the 2 pins on the plug side and the gauge went to zero. I checked ohm from fsv to gauge , it read around 6 .

 

[homelessduck]

From what I have read the senders are no longer available... ?