Question about 1991 Buick Regal

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Fuel Gauge Issue

Fuel gauge never goes below the F regardless of actual fuel level, when it is allowed to sit overnight the needle will lower itself to the right hand side of the full line, but then it is started it steadily turns clockwise another half inch. I was able to remove the clear plastic cover to turn the dial by hand so; when I turn the gauge down to empty by hand, then turn the key to "on" it steadily rises back to past full. it almost sounds like the level sensor is shorted out causing too much resistance in the circuit. looking for second opinion, or even some pointers on how to test the gauge (since I really don't want to drop the tank).

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  • clnielsen Feb 12, 2009

    Thank you for your speedy and experience based response! Is there any way to calibrate these sending units? I'm looking to repair if possible, as opposed to replace.

  • clnielsen Feb 12, 2009

    Well, it was the sending unit, I hooked up a meter and got 0Ω no matter what. it's a problem with the variable resistor making contact with the second contact.

  • clnielsen Feb 12, 2009

    yeah, I got it apart, cleaned it, and found that the little board was indeed shot... luckily, I have some wire identical to the stuff used on the board, and am currently re-wrapping the board with new wire (this is a real pain in the ****, never try it :p)



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I know you don't want to drop the tank and I could lie to you, but the truth is that you have to drop the tank to check and fix this problem. It really is not as hard as you may think. Even easier if you are low on gas. Putting a full tank back up is a real challenge!
So, after you pull the tank down and remove the sending unit/fuel pump, get a ohm meter and set it to Ohms. Insert the leads one into each opening on the connector on the sending unit plug. Slowly raise and lower the arm with the fuel float on it and see if your ohms fluctuate. Also notice if there is any resistance on the arm as you move it up and down. This is how you check your problem. I have seen it many times before. A new sending unit will fix this problem, though if your ohms are fluctuating and your float arm is stiff, you can temporarliy fix it with a few squirts of WD40. It will start to hang up again after a while though.
Please remember to rate this fix.

Posted on Feb 12, 2009

  • Tommy Walker Feb 12, 2009

    No, not officially. However if you can pull the contact out coming from the float arm so that it makes contact with the actual sending unit board you might get it to work. Also, take a pencil eraser and clean the contacts on the arm and the sending unit board. This is assuming that your electrical board is not completely shot. Inspect all of the wires also and clean any corrosion off and be sure the ground is tight. I have fixed them but with varying results. Otherwise a new sending unit will be needed. I looked the part up for you at Auto Zone and they sell the sending unit for $146.99. This should give yu a general guidline as far as price. I hope all of this helps. Good luck.

  • Tommy Walker Feb 13, 2009

    I know, that is why I quit doing mechanics work! Imagine trying to make a living with it, answering questions is much more laid back! Anyway, you will get it. Take your time and check the sending unit before you put it all back together. If the electrical is working then you have fixed it. Be sure to use an emery cloth or fine sandpaper and remove all of the rust from the float arm and any other metal parts before dropping it back in the tank. Spray WD40 on all of the mechanical parts and as an extra precaution after you spray with the WD40, liberally coat all of the same parts with White Lithium Grease. Be sure not to spray any of the electrical components and recheck it AGAIN before you put it back in the tank. It has been a pleasure helping you and please let me know the outcome.



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1997 Cadillac Eldorado fuel gauge not reading fuel level correctly

Did you test before replacing ? Do you know how it work's ?

Fuel Level
The body control module (PZM) monitors the fuel level sender input in order to determine the current fuel level. The PZM filters the input and sends a message via the Class 2 serial data line. The IPC receives this message and displays the current fuel level. The fuel level is sent from the PZM to the IPC at changes of 0.5 L (0.02 gal) or on the request of the IPC, with a resolution of 0.04 L (0.01 gal).
• For the digital IPC, when the fuel level is above 18.5 gal, the IPC displays an F. For readings between 18.5-2.5 gal, whole gallon/liter numbers are displayed. When the fuel level reaches 3.0 gal the message FUEL LEVEL LOW is displayed on the driver message center. When the fuel level reaches 2.5 gal, the IPC displays an E. When the fuel level is 1.2 gal or below the IPC displays a flashing E.
• For the analog IPC, when the fuel level is above 18.5 gal, the fuel gauge pointer is on F. When the fuel level is below 2.5 gal the fuel gauge pointer moves to E. When the fuel level is below 3.0 gal the IPC displays a FUEL LEVEL LOW message.
If the updates are not received or a communication error is detected, the IPC performs the following actions:
• For the digital IPC, the fuel gauge is dashed.
• For the analog IPC, the fuel gauge pointer moves to E.

Fuel Gage Inaccurate or Inoperative
Circuit Description
The IPC monitors the fuel level sent by the PZM through the class 2 serial data line. The IPC software controls one of the following two gauge types:
• A digital gauge consisting if a two-digit numeric seven-segment display
• An analog gauge consisting of a needle pointer.
The IPC interpolates and scales the fuel level information that the IPC receives from the PZM.
When you operate the vehicle in diagnostic mode, either in the vehicle diagnostic system or with a scan tool connected, the fuel signal supplied to the IPC is not filtered by the PZM. The unfiltered fuel signal causes the IPC to show real time readings and may be mistaken as an erratic fuel level display.
Diagnostic Aids
Connect a scan tool to the DLC.

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1 Answer

Do I need to take out and and then reinsert the fuel pump fuse to reset the fuel gauge

That won't affect the fuel gauge. Different circuits, entirely. Any issue with the fuel gauge is between the gauge on the dash, a little wiring to the gas tank, and the sender unit inside the tank. In most cases, the problem turns out to be the sending unit inside the tank.

To check the gauge itself for working, you can ground the fuel gauge wire at the gas tank connector, and watch for movement on the gauge, with the key in ON. You take the connector off at the gas tank, find the wire for the fuel level sender (or gauge), and touch it to a good ground- a metal piece on the car frame. If gauge is good, the needle will move either to full or to empty, but you can see the needle move to a new point, when you (temporarily, only temporarily) ground the fuel gauge wire. The key in the switch must be in on. If this causes the needle to move, then the dash gauge is good, and the problem is the sender unit in the tank. This unit has a variable resistor, not too expensive. The fun is getting to it.

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What's your question?fuel pump working but gauge nt working wts can be the cause.

Either the gauge itself, or the wire from gauge to tank, or the sending unit in the tank. Most of the time it is a problem with the sending unit.

They work like this: in the instrument cluster, a small voltage regulator sends low voltage through the gauge, into the wire to tank, and to the sending unit. The unit has a variable resistor that varies according to the fuel level, measured by the float arm attached to the unit. What it (the gauge) actually measures is resistance to ground-the current goes to a ground point after going through the variable resistor in the sending unit.

You can check if problem is the gauge or the sending unit by grounding the fuel gauge wire at the gas tank connector. Pull the electrical connector apart and locate the fuel gauge wire. Jumper that wire to ground on the frame while watching the fuel gauge needle for movement. DO NOT ground it for more than a split second, just touch to ground while someone watches the gauge. If the gauge needle moves at all (will probably go to full or empty), then the problem is the sending unit in the tank. The gauge is good, so is the wire from gauge to tank. I should mention that doing this test can possibly blow the meter (gauges) fuse in the fuse panel- why I said to do it just for a brief moment.

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