gas gauge stuck on empty

[amikk97]

hello all,
I just replaced my fuel sending unit in my 87 sierra 1500. I put in a brand new sending unit and when I was done, I added about 3 gallons of gas to the tank which was pretty much empty. i turned the key to the on position and could hear the pump priming, however the needle went all the way over to empty (it was stuck past full position since my old sending unit was bad) and it hasn't moved since. i added about 2 more gallons and it hasn't budged one bit. my truck starts and runs and drives fine. I tried rocking the truck back and forth to see if i could get the float to move, and i could hear the gas splashing around, but still nothing on the gauge. ive looked over all the connections and they all seem snug. any know whats going on here? please help

[amikk97]

UPDATE- i just went out and looked and it appears that the middle hose/line on the sending unit got disconnected, as it is no longer on the sender nipple. could this be why the gauge isn't working? i cant put it back without taking the tank down again and i don't really feel like doing that again. is it fine to leave it undone like that? it ran fine without it

[amikk97]

please help guys

[jdf915]

You could try swapping you gauge in the dash.
Posted via Mobile Device

[hatzie]

Hoses have nothing to do with the gauge. Don't run it without fixing the hose.

Usually;

• E = Empty tank or sender wire shorted to ground.
• Reads up to but no more than 3/4 when full = Damaged or loose bias resistor on gauge or bad gauge.
• Reads past full @ 3:00 position = damaged or unplugged sender to gauge wiring or unplugged or damaged sender ground wire. ( on dual tanks bad dash switch [73-80] or bad unplugged valve [81-91] )
  
• Swinging needle while driving = intermittent sender or sender ground wire... OR damaged gauge panel IGN or ground splices.

[1Cobra427]

Hatzie, I was reading your summary of issues and causes. I have the 3rd issue exactly. Left tank on the gauge goes to 3 o'clock and has since I owned the truck no matter if tank is empty or full. My question is the switch you mentioned, it reads correctly for the RT tank. Do I still have a bad switch?

[amikk97]

Originally Posted by 1Cobra427

Hatzie, I was reading your summary of issues and causes. I have the 3rd issue exactly. Left tank on the gauge goes to 3 o'clock and has since I owned the truck no matter if tank is empty or full. My question is the switch you mentioned, it reads correctly for the RT tank. Do I still have a bad switch?

make sure your ground wire is firmly attached to the frame. clean off any dirt around it. if it still is stuck in the 3 oclock position after that, then it is most likely the sending unit, or at least that's what happened with mine.

[hatzie]

Originally Posted by 1Cobra427

Hatzie, I was reading your summary of issues and causes. I have the 3rd issue exactly. Left tank on the gauge goes to 3 o'clock and has since I owned the truck no matter if tank is empty or full. My question is the switch you mentioned, it reads correctly for the RT tank. Do I still have a bad switch?

First I would check for a bad tank ground on the RT side.
The tank ground is easy enough to check visually. It runs from the frame to the ring around the sender. Again... This would be the first place I'd look. Remember just because it looks OK doesn't mean there's wire inside the jacket... GM didn't seal the ground lead so it can corrode completely off inside the jacket and look just fine on the outside. I've found forward lighting harness grounds on the radiator support that looked great but were only held in place by the strain relief crimp on the jacket. Run a jumper from a clean spot on the frame to a clean spot on the pinch weld around the tank... Then check to see if the gauge magically begins to work.

Second I'd check the RT side sender wire and make sure it's not unplugged or damaged. The sender wire is fairly easy to follow between the top of the tank and the plug/grommet where it passes through the firewall.

The switch is dead last of the places I'd look. It's easy enough to test if you don't find a problem with the tank ground or sender wire between the tank and the switch.

• Get your meter and set it to measure OHMS or better yet to the continuity buzzer if your meter has one.
• Pull the switch out of the dash and tie a string loosely around the harness behind the plug, so it doesn't escape back into the dash, then unplug the switch.
• The graphic below is a visual of what is happening inside the switch.
• Test from the centre terminal, marked "Out to gauge" in my graphic, to both terminals marked sender in my graphic. One should buzz.
• Flip the switch to the opposite position and test from the centre terminal, marked "Out to gauge" in my graphic, to the terminal that didn't buzz in the last test.
  If the switch buzzes in both of the above tests then it should be OK.

DPDT 5 terminal GM Fuel Tank Switch for 73-80 dual tanks.

[amikk97]

okay, I have taken to conclusion that its the sender wire shorting to the ground based on the fact when I unplugged the whole sender, it went all the way to 3 oclock position and when I plugged it back in it went to empty again . I also took off the panel and pushed the needle around, but it still falls back to empty. if it is shorted, how do I fix it? I looked over all the wires coming from the sender and they all seem ok, my ground wire is tight against the frame. what should I look for?

[hatzie]

Originally Posted by amikk97

okay, when I unplugged the whole sender, it went all the way to 3 oclock position and when I plugged it back in it went to empty again

Unhooking the sender driving the needle to 3:00 is normal for an undamaged sender wire. If the sender wire was shorted to ground between the tank and the gauge... the gauge would stay on E whether the plug is attached to the sender or not.

However. If the sender is damaged so it shorts the output to ground no matter what the float does OR the float is floating like a rock OR the float is not attached to the wire arm it would do exactly what you describe.

Sounds like you'll be pulling the bed back or dropping the tank again so you can pull the sender to find out.

I am also assuming there's more than 5 gallons in the tank...