1976 Grand Safari fuel gauge problems

Discussion in 'General Automotive Tech' started by 76GrandSafari, Apr 2, 2020.

  1. 76GrandSafari

    76GrandSafari New Member

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    I bought a Grand Safari last fall. I filled the fuel tank fuel and drove it to storage. The gas gauge stayed above full for a while then eventually went down. I parked it and all the fuel had emptied via a leaky fuel line. I replaced the fuel line. Ran out of fuel on way to gas station. Fill it up full. Now the fuel gauge does not work at all. Where should i start looking? If i have to replace sending unit, how does the tank get removed? Underneath or otherwise? I see that it is set up different from a Grand Ville. Thank you for the help
     
  2. OldFox

    OldFox Curmudgeon

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    The most common problem is a bad ground at the sending unit. There is a black wire with a screw going thru it that comes off the sending unit. The connection gets rusty.
     
  3. jaunty75

    jaunty75 Middling Member

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    A few comments:

    1. Oldfox is correct about one possible source of the problem. A gauge that points way above F indicates an open circuit in the gauge wiring. The sending unit is nothing more than a variable resistor with zero Ohms indicating an empty tank and 90 Ohms (typically) indicating a full tank. If there is an open circuit, the dash gauge, which is just an Ohmmeter, is seeing infinite resistance, which is way more than 90, so the needle points well past the F. The easiest and simplest fix, if it is the problem, is to check the ground wire coming off the sending unit where it attaches to the body or frame of the car and make sure the connection is clean and tight. If there is corrosion, dirt, etc, the connection could be poor or intermittent and cause the problem you're seeing.

    2. If confirming the ground is OK does not solve the problem, the next test is to find where the other wire coming off the sending unit (there are two) connects to the wire coming from the front of the car. There will be a pull-apart connector where these wires are joined, and you'll have to trace the wire coming off the sending unit until you find it. (Getting at this connector requires getting at the tank itself. See my post below this one.) Pull this connector apart and connect the side coming from the front of the car to ground. Then turn the key on. The gauge should immediately move to E. Grounding this wire causes the gauge to see zero Ohms, and that corresponds to an empty tank. If the gauge does show E on this test, then you have confirmed that the dash gauge is fine as well as is the wiring from there to the rear of the car. Which means that the problem is the sending unit, and this means removing the tank.

    3. See my post below this one regarding removing the tank. It appears that it's done through the left rear wheel well opening. The tanks on the clamshells are located in the driver's side rear fender, not under the car.

    4. But before you go through all the trouble of dropping the tank, you will want to make sure that a replacement fuel tank sending unit is actually available for your car. I checked rockauto just now, and, while they do show availability of a fuel tank for your car, they do not show a sending unit. You might end up having to have yours rebuilt.
     
    Last edited: Apr 2, 2020
  4. jaunty75

    jaunty75 Middling Member

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    I was able to find a factory service manual for 1972 Pontiacs online. That was the latest model year I could find, but I imagine the procedure for removing the fuel tank on a '72 Pontiac clamshell is the same as on a '76. Below are the relevant pages out of that manual. It appears that the tank can be removed through the left rear wheel well. The procedure for the B-series wagons basically starts at step 5 below.

    Capture.JPG

    Capture2.JPG

    Capture3.JPG
     
  5. HotRodRacer

    HotRodRacer Moderator Staff Member Moderator

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    The guys above have given some great info if the gauge reads FULL all the time. You only state it dies not work at all, not whether it reads EMPTY or FULL. Please clarify.

    If it reads EMPTY all the time (or close to it), check the float for leaks and replace as needed. Once they split or rupture, then the gas gets inside of them and they no longer... well, they no longer float. That causes the ohms to read low, which in turn reads EMPTY or close ot it on the gauge.

    Just something else for you to check if it reads the other way opposite what Jaunty and OldFox gave you.
     
  6. jaunty75

    jaunty75 Middling Member

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    The floats on these things are not rigid balloons like used to be found on toilet valve floats. Those could never be relied on to last even a reasonable amount of time in an inaccessible location like the fuel tank on a car. The floats are typically a foam or rubber or other lightweight material that is gasoline-resistant and not subject to rupturing. It is very unlikely that the float itself is the cause of this problem. After all, a float that was not floating would not cause the gauge to read past F, which he DID say occurred at one point. The problem is almost certainly electrical , and whether it's a short or an open circuit, one way or the other, he's very likely going to have to remove the tank. Once he goes through all that trouble, he might as well have the sending unit fully rebuilt if he is unable to find a new one.

    Here's a typical replacement sending unit. The float is a piece of solid, lightweight rubber.

    spectra premium FG110B.jpg
     
  7. 76GrandSafari

    76GrandSafari New Member

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    Thank you all so much for the replies. I will have access to the car tomorrow and will check the ground and the gauge. To clarify, I cannot tell if it is below empty or above full as i cannot see the needle at all.
     
  8. jaunty75

    jaunty75 Middling Member

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    If you can't see the needle at all, my guess is that's because it's well past the F mark. I don't think the needle can physically move lower than the E because you can't get lower than zero Ohms. Unless, of course, the gauge is physically broken. Which I doubt. If it is stuck way past the F, this is all the more indication that there is an open circuit. By the way, where the needle comes to rest when the ignition is off, if you were wondering, means nothing. There is no power to the gauge when the key is off.

    Please let us know how you make out in regard to getting at the sending unit ground. As the diagrams indicate, it appears getting at the sending unit ground will require removing the gas tank, so this isn't going to a five-minute job. I would be interested to know if there is in fact a way to get at the ground connection without removing the tank.

    Another comment: Unlike the sending unit ground connection for a non-station wagon, where the ground is up under the rear of the car but is still usually well-exposed to the elements, the ground in these wagons appears to be well up inside the left-side fender and well away from water and salt and whatever. This would lead me to suspect that, while anything is possible, the ground connection in your car is probably fine, and your issue will turn out to be a failed sending unit.
     
  9. 76GrandSafari

    76GrandSafari New Member

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    UPDATE: I got ambitious and went to the storage location to have a look at the ground wire. The ground wire was relocated to the frame rail by a previous owner with a sketchy crimp connection to the old wire. The old terminal was still in the inner fender wall but disconnected. I removed his crimp connection and replaced it with a soldered connection and put a new terminal on the frame rail. I wire brushed and sanded so the connection was definitely good at that point. Fuel gauge still does not work. I cannot see the needle on either side of the E or F on the gauge. I suppose i will drop the tank and check sending unit.
     
  10. jaunty75

    jaunty75 Middling Member

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    Interesting. The fact that a prior owner got in their and did who knows what to the wiring means that all bets are off now as to what you might find. Be prepared for anything up to and including Jimmy Hoffa!
     
  11. 76GrandSafari

    76GrandSafari New Member

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    Yeah i let out a big sigh when i saw it. Oh well. All gauges work except the fuel and the clock.
     
  12. 76GrandSafari

    76GrandSafari New Member

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    Removed sending unit today. Lost continuity across the pin that goes through the cap. Removed and rebuilt with some solder and new wires. Reinstalled and the gauge works.
     
  13. jaunty75

    jaunty75 Middling Member

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    Yay! Wish they were all that easy.
     
  14. HotRodRacer

    HotRodRacer Moderator Staff Member Moderator

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    That's awesome, glad you got it fixed.
     
  15. Silvertwinkiehobo

    Silvertwinkiehobo "Everything that breaks starts with 'F.'"

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    Alright! I love righteous, straightforward repairs!
     

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