BillGrissom
Well-Known Member
While my 64 Valiant cluster was out, I tested & fixed the fuel gage reading. Since then, Kit Carlson posted a "tweaker box" design you could add to the body wiring to adjust the reading without removing the cluster.
I connected the fuel gage (removed) to my new electronic Vreg and fuel sender on the bench. The new sender (1A-FSU-00007, ebay $45) had an immediate issue. It didn't read correct or smoothly. I popped off the cover and bent the pot wiper to touch better. It then output correctly (9 ohm "F" to 90 ohm "E"). But the dash gage didn't read correct.
The needle stopped at 3/4 F, even w/ Vreg @ 8 V. By turning the 2 slotted adjustments on the gage, the needle got to "F" (Vreg @ 7.5 V), but the needle hit "E" w/ sender mid-point (20 ohm). For a 2-pt calibration you need 2 knobs to turn. For the 2nd "knob", it seems a resistor in parallel w/ sender should work. A few calcs suggested 26 ohm would read "E" correctly (sender 90 ohm), and a simple addition between ring terminals on the cluster (2nd photo). Tweaking Vreg and the gage slots a bit more, it now reads smoothly from "E" to "F", with no dead-zones at the ends. Still may not be perfect installed since the sender stops may not match the tank level limits, plus resistance in the body wiring.
It is possible my fuel gage was so far off because I boogered the delicate thermal arm inside when I opened it to slip heat shrink over the internal Vreg (disable). Initially, I started opening the gage from the back, until I found you must drill out one rivet on the front panel. I super-glued the panel back.
Some will point that changing Vreg can affect the coolant temperature gage. Mine didn't read anything at first (gage measured infinite ohms), so popped it open (drill a rivet) and found the wire broken. I wrapped a very thin Cu wire around the stub wire left off the arm and soldered it, then soldered the new Cu wire to the output stud. The factory wire is likely Ni-Cr so doubt solder sticks, but it does hold the Cu wire tight. The factory used some pink adhesive at the stud, which I picked off to bare Cu. With a 20 ohm resistor to gnd, simulating the sensor, the gage now reads "ideal" temp (1st tic, just below half scale).
I searched for the sensor specs. Nothing in my 65 Dart shop manual, nor Haynes, and even rockauto and such give conflicting info about correct PN;s, even listing on/off sensors. I suspect most gage-type sensors have identical response and just vary in pipe thread and output connector. I put a TS-18 in my 65 Dart (mushroom connector), whereas my 64 Valiant has a threaded-stud type (can't read stamp). They are 318 & 363 ohm, resp. at 61 F. I'll post if I find manufacturer specs.
Below are paths to pursue. I hit a similar "dry hole" searching for specs on the temp sensors in my 85 M-B. Please post if you have specs on the temp sensor.
http://www.aa1car.com/library/coolant_sensors.htm
NTC thermistor plot: www.learningaboutelectronics.com/Articles/Thermistor-resistance.php
From chart, if R = 300 ohm at 60F, then R = 20 ohm at 203 F, 10 ohm = 257 F.
Microsquirt GM temp sensor: www.useasydocs.com/details/clt.htm
Degrees F, Ohms
-40º, 100700
0º, 25000
20º, 13500
40º, 7500
70º, 3400
100º, 1800
160º, 450
210º, 185
88-93 Ford: www.usnaaaa.com/pingisgone.pdf
I connected the fuel gage (removed) to my new electronic Vreg and fuel sender on the bench. The new sender (1A-FSU-00007, ebay $45) had an immediate issue. It didn't read correct or smoothly. I popped off the cover and bent the pot wiper to touch better. It then output correctly (9 ohm "F" to 90 ohm "E"). But the dash gage didn't read correct.
The needle stopped at 3/4 F, even w/ Vreg @ 8 V. By turning the 2 slotted adjustments on the gage, the needle got to "F" (Vreg @ 7.5 V), but the needle hit "E" w/ sender mid-point (20 ohm). For a 2-pt calibration you need 2 knobs to turn. For the 2nd "knob", it seems a resistor in parallel w/ sender should work. A few calcs suggested 26 ohm would read "E" correctly (sender 90 ohm), and a simple addition between ring terminals on the cluster (2nd photo). Tweaking Vreg and the gage slots a bit more, it now reads smoothly from "E" to "F", with no dead-zones at the ends. Still may not be perfect installed since the sender stops may not match the tank level limits, plus resistance in the body wiring.
It is possible my fuel gage was so far off because I boogered the delicate thermal arm inside when I opened it to slip heat shrink over the internal Vreg (disable). Initially, I started opening the gage from the back, until I found you must drill out one rivet on the front panel. I super-glued the panel back.
Some will point that changing Vreg can affect the coolant temperature gage. Mine didn't read anything at first (gage measured infinite ohms), so popped it open (drill a rivet) and found the wire broken. I wrapped a very thin Cu wire around the stub wire left off the arm and soldered it, then soldered the new Cu wire to the output stud. The factory wire is likely Ni-Cr so doubt solder sticks, but it does hold the Cu wire tight. The factory used some pink adhesive at the stud, which I picked off to bare Cu. With a 20 ohm resistor to gnd, simulating the sensor, the gage now reads "ideal" temp (1st tic, just below half scale).
I searched for the sensor specs. Nothing in my 65 Dart shop manual, nor Haynes, and even rockauto and such give conflicting info about correct PN;s, even listing on/off sensors. I suspect most gage-type sensors have identical response and just vary in pipe thread and output connector. I put a TS-18 in my 65 Dart (mushroom connector), whereas my 64 Valiant has a threaded-stud type (can't read stamp). They are 318 & 363 ohm, resp. at 61 F. I'll post if I find manufacturer specs.
Below are paths to pursue. I hit a similar "dry hole" searching for specs on the temp sensors in my 85 M-B. Please post if you have specs on the temp sensor.
http://www.aa1car.com/library/coolant_sensors.htm
NTC thermistor plot: www.learningaboutelectronics.com/Articles/Thermistor-resistance.php
From chart, if R = 300 ohm at 60F, then R = 20 ohm at 203 F, 10 ohm = 257 F.
Microsquirt GM temp sensor: www.useasydocs.com/details/clt.htm
Degrees F, Ohms
-40º, 100700
0º, 25000
20º, 13500
40º, 7500
70º, 3400
100º, 1800
160º, 450
210º, 185
88-93 Ford: www.usnaaaa.com/pingisgone.pdf
