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Old August 23rd, 2011, 12:51 PM   #1
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fuel gauge pegged F - whats next?

Ok, so after reviewing a few posts here, I spent the greater portion of the evening trying to remedy my fuel gauge that is pegged past full (67 442). I checked the ground at the sender - ok. grounded the brown wire at the sender connection, connection to middle ribbon harness, and at the connection to dash harness - no movement from past full. replaced the gauge with two others I had, they moved to past full. What does this mean?
Gauge worked before I replaced dash and harness. I have power to the upper left bolt on fuel gage (looking from driver seat). Any help on next steps sure would be appreciated. The pad of sticky notes with odometer readings in my console is not looking cool.
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Old August 23rd, 2011, 01:36 PM   #2
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Sounds like an open circuit in that new harness. broken/ corroded wire or bad connection? You'll have to trace the circuit checking for continuity.
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Old August 23rd, 2011, 01:39 PM   #3
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So you think open in between the gauge and the connection to the ribbon harness?
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Old August 23rd, 2011, 01:44 PM   #4
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A fuel gauge pegged past Full is definitely due to an open circuit (infinite resistance). You need to start at the gauge and trace the wiring until you find the break.
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Old August 23rd, 2011, 01:45 PM   #5
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I thought pegged full was a bad ground?
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Old August 23rd, 2011, 01:48 PM   #6
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What would be the test? from the brown wire at connector to one of the posts on the gauge? I know upper left is hot, which other is brown wire? upper rt, or lower center?
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Old August 23rd, 2011, 01:50 PM   #7
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A bad ground is potentially the same thing as an open circuit. But, in the case of the gas gauge, the ground is at the other end of the circuit. Two wires come off of the sending unit. One is the ground, and it's connected directly to the frame or body. If it's missing or bad, it will cause an open circuit and the gauge to peg on F.

If the ground is good, there can still be an open circuit because there is a break in the OTHER wire coming off of the sending unit. This wire goes from the tank all the way to the gauge. If it's broken anywhere along the way, that's an open circuit and will have the same effect as a bad ground. Either way, the gauge goes to F.

IF the gauge is working properly, you should be able to take the wire coming from it, ground it, and have the gauge peg at the other end, on Empty.
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Old August 23rd, 2011, 01:55 PM   #8
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Originally Posted by roscopdoggy View Post
What would be the test? from the brown wire at connector to one of the posts on the gauge? I know upper left is hot, which other is brown wire? upper rt, or lower center?
I don't know enough about the way in which the fuel gauge in your particular car is wired at the gauge, so I don't know what you mean by "upper right" or "lower center."

Again, find the wire that comes from the gauge. If you don't know what color it is, you need a chassis service manual with a wiring diagram. On my car, it's orange. I have a '67 Delta and you have a '67 Cutlass. I'm guessing the wire colors are the same.

Once you have that wire, start following it backward. Eventually, you should come to a spot where it is broken or where there is a connector open.
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Old August 23rd, 2011, 03:13 PM   #9
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Other things to consider:

Power to the gauge comes from a 9-amp fuse labeled "instruments." It's the same circuit that provides power to the warning lamps. If you haven't already done so, check this fuse. If it's ok, you might want to check the other warning systems, and you can't do this by just starting the engine and seeing if the warning lights go on momentarily like they're supposed to. That's a separate circuit that tests only the bulbs themselves. The only way to check that power is getting from the 9-amp fuse to the warning lamps is by pulling the connector off of the oil pressure or water temperature sending unit and grounding it. With the ignition on, the appropriate warning lamp should come on.

If the fuse is OK and these other warning lamps work as they should, then the problem goes to back to what we've been saying. Assuming the ground is OK, it's most likely to be an open in the line from the gauge to the sending unit.

Last edited by jaunty75; August 24th, 2011 at 06:32 AM.
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Old August 23rd, 2011, 04:50 PM   #10
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My 68 442 did the same thing. It would move some but pegged way past all the time. I replaced with another gauge and now stays pegged way past full until 10 gal down and then it starts moving towards half. I wounder if it is a calibration issue?

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Old August 23rd, 2011, 04:56 PM   #11
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It probably wasn't the gauge at all. It is more likely the sending unit. Nothing is adjustable, so it can't be calibrated. These things are not that sophisticated. They're just 90-ohm resistors, with the full resistance present when the sending unit is in the Full position and zero resistance when in the empty position. That's why, when there is an open circuit, which is infinite resistance, which is much larger than 90, the gauge doesn't just go to F, but goes way past it.

You probably need a new sending unit.
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Old August 23rd, 2011, 05:45 PM   #12
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When the gauge is out of the car what position should the needle be in? The old one and the replacement were beyond full.
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Old August 23rd, 2011, 05:48 PM   #13
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Sounds right. They're not connected to anything. Open circuit = infinite resistance = pegged past Full.
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Old August 23rd, 2011, 05:57 PM   #14
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Quote:
Originally Posted by roscopdoggy View Post
Ok, so after reviewing a few posts here, I spent the greater portion of the evening trying to remedy my fuel gauge that is pegged past full (67 442). I checked the ground at the sender - ok. grounded the brown wire at the sender connection, connection to middle ribbon harness, and at the connection to dash harness - no movement from past full. replaced the gauge with two others I had, they moved to past full. What does this mean?
Gauge worked before I replaced dash and harness. I have power to the upper left bolt on fuel gage (looking from driver seat). Any help on next steps sure would be appreciated. The pad of sticky notes with odometer readings in my console is not looking cool.
Did you ground the sender terminal at the guage. If it goes to empty there, it's an open in the printed circuit board on the back of the cluster. I don't think you have a bad sender since you grounded the system up from there. The easiest test is to unplug the sender wire (brown you said) then test that circuit with a test light for power at each connection point until you lose the light then backtrack that particular section until you pinpoint the break.
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Old August 23rd, 2011, 06:28 PM   #15
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Smile Fuel Gauge

I'm going through this fuel gauge thing myself in my 56 Olds. My gauge reads "Full". Sometimes it won't go to full right away - it needs time! We tested the ground and sending unit - all was fine. Used a tester. We pulled out the gauge, which was the last attempt. Seems like the gauge is fried. There are two coils with wires - one was a reddish color and the other sort of orange. Looks like the orange spool was fried!

When I took the gauge out (not hooked up at all) it remained on "E" unless I turned it upside down then it would move to full. Don't know what that means though!!!

I sent the gauge away to the gauge hospital for restoration. I know when it comes back it will work - although, will everything else work!!! Too bad there isn't a handbook to pinpoint the problem so we can know what we are dealing with. Wouldn't it be nice to use a modern gauge with an old car - pull out the guts and modernize it (EXCEPT FOR THE FACE).
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Old August 23rd, 2011, 06:40 PM   #16
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Okay...I just got my old gauge and hooked a AA battery to the posts that operate the gauge. I could move from empty to full based on polairIty. I could also take the power off and set the gauge to any position and it will stay. My gauge on the counter is set to 1/2 now. Both gauges were pegged. When I removed the original it was pegged (the one I just set to 1/2) and the replacement used gauge was pegged. My theory is that the gauge needs to be set to 1/2 when installed. The movement is relative to the position it is set at. May also be hog wash. This weekend I will replace the gauge set at 1/2, plug in and fill up. I am about 1/2 tank based on miles now.

I had a 40amp fuse blown on the stereo when I got the car. Maybe a power surge can screw with 1/2 tank setting (nominal)?

Thoughts? Or hog wash? Dave
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Old August 23rd, 2011, 06:58 PM   #17
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Fuel Gauge

Dave, your theory sounds good. Especially with a power surge which could throw gauges out of wack. Hopefully you are correct and your problem will go away. Mechanical gauges can do strange things!

Good luck. Hope all works out.
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Old August 23rd, 2011, 07:22 PM   #18
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It's hogwash.

You need to systematically test your gauge connections.

Start at the gauge. With the hot gauge terminal connected to a hot source, the gauge grounded, and the sender terminal connected to ground, the gauge should read Empty.
Disconnect the sender terminal from ground, and it should go past Full.

Now go to the sender and do the same thing - disconnect it, and ground the sender wire - the gauge should go to Empty. If it does, all your wiring to that point is good, and the problem is either the sender, or the sender ground.

If you drop the tank and remove the sender, you may be able to repair it by disassembling it and cleaning the coil and the wiper and re-contouring the wiper to press against the coil.
You can also test it - float down = ∞ resistance, float up = 90Ω.

Good luck!

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Old August 23rd, 2011, 07:33 PM   #19
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On a 66 or 67, there are 3 small bolts holding the gauge and making connections in the circuit board. Does anyone know for sure which is which? To me, it looks like upper left is hot, upper right is sending unit, and bottom center is ground. Anyone know?
Knowing what each is will be very helpful in systematically testing.
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Old August 23rd, 2011, 07:44 PM   #20
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So I can identify the two terminals .......What color wires go to hot & sender?

Again ...68 442

Thank you,
Dave
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Old August 24th, 2011, 06:29 AM   #21
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If everything worked before the dash harness change, I would focus on the connector between the dash and body harness and the connections at the gage. I agree with everything jaunty75 wrote. Think of it this way, power flows to the gage, through the coil that moves the needle, then from the gage to the sender where the rheostat controlled by the float regulates the resistance of the circuit. Power then leaves the sender and returns to a chassis ground. The higher the resistance, the higher the needle reads and vice versa. Thats how the system works. Have you used an ohm meter? Check for continuity (unbroken flow) between each end of wire from body harness to the gage, and probe the body side of the connector to make sure the terminals are good.
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Old August 29th, 2011, 11:46 AM   #22
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I've read through this thread carefully and I think I have the exact opposite problem. My gauge reads way past EMPTY when the ignition is in the OFF position. Once the ignition is in the ON position the needle moves to just above EMPTY.

I'm just beginning my investigation to determine the issue. Any recommended first obvious steps I should take?

Thanks

Oh yeah, 72 Cutlass, 350 and yes the tank is full.
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Old August 29th, 2011, 12:24 PM   #23
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You DO have the exact opposite problem.

You've got a short in the sender wire, somewhere between the gauge and the sender, possibly including the sender itself.
The good news is, your grounds are good.
The bad news is, you've got to trace the problem back to it's source. Just disconnect the wire at every plug, one at a time, and you'll find a place where it goes to Full - the short is past that point.

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Old September 7th, 2011, 06:48 AM   #24
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Well mine is doing the same thing so I checked this thread out. I have a new circuit board in the dash and a new tank and sending unit. well I turned the key on and it read full had the wife watch the gauge and I went under the car and grounded the lead from the gauge and no diff then I got out and reached under the dash and bumped the harness that plugs into the circuit and the gauge went to empty(the tank is empty) so I would say its a good chance you have the same problem. Now does anyone know where I can find the new plugs for the harness? Im thinking every bump I hit is going to be a problem

Last edited by archeryshooter; September 7th, 2011 at 06:50 AM.
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Old September 8th, 2011, 08:30 AM   #25
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If you want to keep it original and save some cash (if not time), you can try pulling the terminals out of the connectors ONE AT A TIME so they don't get mixed up, and cleaning them with a wire brush. To remove a GM terminal you stick a paperclip into the open side (opposite the wire) and push down a retaining tang, then pull. I've done this many times with success. If the terminals are too corroded to clean, they can be repaced individualy. I know this works for in-line connectors. If you're working on the connector at the cluster itself, I've never had to deal with one of those, so I'm afraid all this may not apply. Try to clean the connection best you can and go from there.
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Old September 8th, 2011, 09:58 AM   #26
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Tony ,
Have you checked with American Auto Wire in New jersey.
I have dealt with Donny Bock Great Guy.
They may offer just the Crimp End on that.
I have just gutted 2 -66 harnesses.
I have the end plug and the wires with an 8 inch pigtail if you think that will help.
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Old September 8th, 2011, 10:11 AM   #27
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Tony ,
Have you checked with American Auto Wire in New jersey.
I have dealt with Donny Bock Great Guy.
They may offer just the Crimp End on that.
I have just gutted 2 -66 harnesses.
I have the end plug and the wires with an 8 inch pigtail if you think that will help.
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I will do that
you had some problems with yours as well didnt you Ron? seems to be pretty common
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Old June 30th, 2012, 04:41 PM   #28
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I just had this problem too. New tank and new sending unit. Checked resistance between both wires off of sending unit @ 95ohms. Tank is nearly empty. Just before I started to remove what I thought was a bad sending unit, I figured what the heck, and gave the tank a few "love taps" with a rubber mallet, and all of the sudden it went to 5 ohms! Apparently float was stuck in the raised position causing the problem. These threads have helped me out so many times, just wanted to add my lesson learned.
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Old July 1st, 2012, 05:36 AM   #29
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My problem ended up being the sending unit. After I replace it everything works great!
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Old July 9th, 2012, 07:53 AM   #30
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fuel gauge pegged F ----SOLVED

Ok guys -
Problem solved! I actually had two things going on. First, after testing from the RP harness connector to the gauge, I found I had a break between the gauge and the sending unit somewhere in the printed circuit. I placed a jumper wire, and still pegged on F. Then, I found that somehow the right hand (when viewed from the front) screw was not contacting the metal bracket behind the gauge. Once I moved the jumper wire from under the screw to under the gauge (between gauge and bracket) it worked! Hope this helps anyone else.
Thanks for all the help.
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Old August 9th, 2012, 09:12 AM   #31
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just fix mine

guys, started my car up the other day and the fuel gauge went to 3 oclock... on my 70 w30 conv. 3 oclock position. i just found a dirty ground above the tank...cleaned the contact point, put on an new wire end and bam, work great...............great site.....thanks Bear......
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Old August 9th, 2012, 06:11 PM   #32
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Glad to hear it! Nothing like a working fuel gauge.
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Old August 9th, 2012, 06:11 PM
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