I remember seeing a posting of fuel gauge fluctuation with the use of the directionals . I have a similar problem with my fuel gage not reading accuratly and when i put my foot on the brake pedal the gauge seems to read correctly . i don't seem to have any interaction with my directionals any thought on this possible bad ground at sender or gauge ? thanks steve
-
-
Re: 61 corvette fuel gauge and stop lamps
I had this problem on my 61. I ran an extra ground wire from the sender to the frame and it cured the problem. My fuel gauge still reads low, but it does not fluctuate with the brake/signal lights as it did before adding the extra ground. I think the low reading is probably a sender calibration issue an unrelated to the ground. -
Re: 61 corvette fuel gauge and stop lamps
Fuel gauge in early Corvettes is based on in-line ammeter from B+ supply voltage (battery) to ground through the tank sender's variable resistance. Since gauge is a simple ammeter, it WILL respond to fluctuations in supply voltage that cause perturbation in line current. These cars (not just Corvette, car & truck vehicles of the same era too) are notorious for erratic gas gauge 'funnies'....
The 'acid' test is to see what the tank gauge reads with the engine off and the ignition on, then start the engine and watch the guage change its reading as the voltage regulator senses the need to charge the battery and the alternator or generator turn on and pump the battery back up by supplying 14-16 VDC. The poor little gas gauge fluctuates accordingly with absolute battery supply voltage!
'Tricks' abound in the electrical system to 'smooth' transient turn on/off by various high energy consuming branchs (turn signal, heater blower fan, headlights, Etc.) by strategically placing capacitors here/there to 'damp' the branch circuit's instantaneous current draw. Bottom line, these 'tricks' are only effective IF they restrict the branch circuit's dV/dt to the window of the voltage regulator's sense/switch reaction interval AND cars equipped with a generator are operating at sufficient engine RPM to deliver a net charge....
Mid-year Corvettes saw the introduction of the alternator (faster responding current supply and MUCH more efficient net energy production at low engine RPM). Still, designers weren't happy with the overall picture and complicated the circuit topology of the gas gauge by rolling the tank sender unit into a Whetstone bridge design. This made the gauge INDEPENDENT of absolute supply voltage at the cost of added inductor/resistor components and redundant wiring. You'll see the tank sender for mid-year cars has two terminals on it instead of the single terminal used on earlier as well as later cars. This is to implement the Whetstone bridge wiring topology of the sender.
Finally, solid-state electronics progress down the learning curve sufficiently to generate inexpensive 3-legged voltage regulator components. It became feasible to go back to the older/simpler in-line ammeter setup and just 'slap' a solid-state voltage regulator onto the B+ supply line for 'critical' dash elements (fuel gauge, temp gauge). End of story....
Bottom line, yes fluctuations can/do happen on the older cars. How much is 'excessive' requires one skilled in the art of doing Performance Verification. If you have a car that demonstrates 'excessive' fluctuation, it's probably due to any number of factors including (1) poor/corroded ground contacts, (2) smoothing capacitors that are defective or internally leaking from age, (3) the voltage regulator/generator setup is over the hill and in need of rebuild or replacement, and (4) previous owners have jury rigged wiring harness repairs and/or modifications so 'baby' tain't configured as she was originally designed....Comment
-
Poor Taillight Harness Ground - Culprit
Interaction of the fuel gauge needle and the turn signals is caused by a poor ground for the taillight harness - this ground connection serves both the rear lights AND the fuel tank sending unit; you will see the same thing when you step on the brakes. Cleaning and re-securing the taillight ground connection will restore normal function, but adding a dedicated ground wire for the fuel tank sending unit to the frame is the ultimate cure.
JohnComment
Comment