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I have only driven my 69 Cutlass several times and put a bit of gas in it over the past 6 months so I have only observed the gauge at 1/4 to 1/2 of a tank. I filled it up the other day and it went up to full. As I continued driving it went past full and into the temp light area. It has been at a mechanics since then and he asked if I had driven it at night. I hadn't, but he had and said the headlights would get bright and then dim and then bright and he figured I had a regulator issue. I'm wondering if that is what's happening to my fuel gauge. Anyone have a similar experience?
The headlights will go bright driving at speed and dim if your at idle. Too low of an idle and/or low battery voltage will exacerbate the issue. If you filled the tank all the way into the filler tube the gas gauge will point past full. I would observe it and see what happens when you drive it a while and use fuel.
It sounded more like while driving at a steady speed the brightness fluctuated. I should hopefully get it back today and will drive it at night and see better what's going on. I just had all new front suspension and rear control arm bushings as well as distributor done so hopefully it will feel like a different car.
thanks,
Steve
If you have checked the alternator and all is well... an external Voltage Regulator this is usually was causes the flickering lights. Needs adjusted or replaced.
Fuel gauge issues of not showing the correct fuel level...my experience after replacing the fuel gauge sending unit = Bad ground.
Just few demons I chased for those issues that took care of it.
As I continued driving it went past full and into the temp light area.
This is the classic symptom of an open in the fuel gauge circuit. It could be a bad ground connection where the ground wire from the sending unit attaches to the frame of the car in the front of the gas tank. It could also be a bad sending unit. The first test is to disconnect the sending unit from the wire coming from the front of the car. Ground the wire from the front and turn the key on. The gauge should go to E. Then remove it from ground with the key on, and it should go past F again. If it passes these tests, the gauge and the wire from the gauge to the rear of the car are fine. Next check the ground. If that's ok, it's likely the sending unit.
I have owned a 1967 442 (1969-1971), a 1972 442 (1975-1979) & a 1971 CS Convertible (July, 2018 - present). Each one of these vehicles fuel gauges operated exactly as (the other) Eric described - when you fill the fuel tank all the way up and into the filler tube, the fuel gauge points past full until you burn off ~20 miles (~1.5-2.5 gallons fuel).
A bad ground or otherwise open circuit (infinite resistance) will cause the gauge to go past full. A short in the tan wire going to the sender (low resistance) causes the gauge to read empty. Sounds to me like you have a bad ground which is pretty common.
Each one of these vehicles fuel gauges operated exactly as (the other) Eric described - when you fill the fuel tank all the way up and into the filler tube, the fuel gauge points past full until you burn off ~20 miles (~1.5-2.5 gallons fuel).
Originally Posted by Vintage Chief
If you have infinite resistance the fuel gauge will read FULL ALL THE TIME.
Yes, but there is a difference between "points past full" and "points past full." The behavior described here is what I see all the time with my 2013 Nissan Truck. The fuel gauge points a few ticks past the F mark when I fill up. My '78 Toronado does the same thing.
But it is completely different when the gauge wiring has an open circuit because the resistance is not 90 ohms, but rather is "infinite" ohms, and, since the gauge is just an ohmmeter with a pointer attached, the needle will point much further past F. It will be so far past the F that you will know there is a problem
Here's a photo of the gas gauge on my '67 Delta, where I had this exact problem. When I fill the tank now, it's not uncommon for the needle to be pointing where the green arrow points. That's very typical. But when the sending unit stopped working, the gauge needle went all the way over to where the yellow arrow points, and there is no way that that is normal behavior when the tank is full.
To quote the OP:
As I continued driving it went past full and into the temp light area.
Going far enough past F that it is pointing at indicator lights is not normal behavior. If this persists, he has a fuel gauge wiring problem.
Yes, but there is a difference between "points past full" and "points past full." The behavior described here is what I see all the time with my 2013 Nissan Truck. The fuel gauge points a few ticks past the F mark when I fill up. My '78 Toronado does the same thing.
But it is completely different when the gauge wiring has an open circuit because the resistance is not 90 ohms, but rather is "infinite" ohms, and, since the gauge is just an ohmmeter with a pointer attached, the needle will point much further past F. It will be so far past the F that you will know there is a problem
Here's a photo of the gas gauge on my '67 Delta, where I had this exact problem. When I fill the tank now, it's not uncommon for the needle to be pointing where the green arrow points. That's very typical. But when the sending unit stopped working, the gauge needle went all the way over to where the yellow arrow points, and there is no way that that is normal behavior when the tank is full.
To quote the OP:
Going far enough past F that it is pointing at indicator lights is not normal behavior. If this persists, he has a fuel gauge wiring problem.
I would agree. "If" it really is REMAINING stationary at the TEMP lamp indication then it's faulty infinite resistance ground issue. I think we'll need to see if it starts working it's way back down as the fuel level lowers. However, the fact it was working between 1/4 and 1/2 leads me to suspect otherwise (at the moment at least for this 30 ohm unit).
Last edited by Vintage Chief; October 11th, 2019 at 03:41 PM.
Reason: sp temp/hot
I have only driven my 69 Cutlass several times and put a bit of gas in it over the past 6 months so I have only observed the gauge at 1/4 to 1/2 of a tank. I filled it up the other day and it went up to full. As I continued driving it went past full and into the temp light area. It has been at a mechanics since then and he asked if I had driven it at night. I hadn't, but he had and said the headlights would get bright and then dim and then bright and he figured I had a regulator issue. I'm wondering if that is what's happening to my fuel gauge. Anyone have a similar experience? Steve
I'm betting its just fine and nothing is wrong. I have owned many GM cars that went past full. Thats why the car goes so far "on a half tank" when its filled up. But the half tank to empty goes really fast. Some people gauge fuel mileage based on the gas gauge needle and miles. .......Just my two cents worth.
This is exactly what happened to mine. It wasn't very accurate but one day while driving on the interstate, I noticed the needle jumped up to the hot light. It did turn out to be a bad ground. I dropped the tank and found the wiring badly corroded and barely hanging on. I ended up replacing the sending unit. Now, all is well.
Sorry dude. It's kind of a pia.
October 11th, 2019, 05:42 AM
