cruiser
Well-Known Member
Hi Guys and Gals. I know this topic has been visited many times, but I recently solved a long standing fuel gauge problem with my 1974 Duster and I'm passing along what I've learned. Let's start with the basics. My 225 auto Duster is very stock and original, including all electrical wiring. I replaced the gas tank with a new stock tank. The gauge cluster was professionally rebuilt with a solid state voltage limiter installed in the back of it. When I bought the car in 2019, the fuel gauge was really inaccurate, reading half full only forty miles after a fill up. I pulled the sending unit, and it wasn't the original one but it was a correct Chrysler part for the car. I replaced the sending unit with an aftermarket stainless steel one from NAPA and it wasn't much better - probably because they're made in Taiwan and calibrated incorrectly. After much testing and experimentation, I have now created a fuel quantity system that works accurately and reliably. Here's what I've learned. Maybe this will help you. First, I ran the engine dry of fuel, then filled it up all the way. "All the way" means letting the fuel nozzle turn off when it's full, then clicking the nozzle one more time to ensure that the system is all the way full. When I did this, the system took 15.1 gallons of gas, even though the owner's manual says that this is a 16 gallon tank. So this means that between the tank and filler neck, the system capacity is 15.1 gallons of gasoline. I then installed a Meter Match fuel gauge calibration unit. When the tank was empty, I removed the sending unit and calibrated the two end points of the fuel sender: Float all the way down (empty), and float all the way up (full). This calibrates the entire range in a linear scale, correcting the inaccurate logarithmic scale of the sender from the Taiwanese factory. Next, I did a series of proving runs with the car, consisting of steady state speed runs at 70 mph, starting with a full tank and running it down to 1/8 tank. Here's what I learned: At 70 mph, I get 15 mpg. With 15.1 gallons of useable fuel, that means that the car has an extreme range of 227 miles before the engine quits. I assumed that the filler neck holds about 1.5 gallons of gas, which means that there will then be 13.6 gallons of useable fuel remaining in the tank. I calibrated the upper end of my fuel gauge to read slightly over-full when the I gas up the car. In this way, the engine burns the filler neck fuel and the gas gauge needle moves down to the "full" mark when it begins burning tank (not filler neck) fuel. So going forward, if you do the math this means that every quarter of the fuel gauge represents 50 miles of range. Bottom line: 200 miles of range from "Full" to "Empty" on the gauge, after burning 27 miles of fuel from the filler neck. I then calculated and calibrated the 3/4 and 1/4 positions on the fuel gauge with the Meter Match. It was easy, and now I have a very accurate gas gauge in my Duster. If I drove at a steady 50 mph for an entire tank, I'm sure that I could get better mpg and range. So here's what you need to do to fix your A body inaccurate fuel gauge. 1: Install a new tank. At least you now know that you've got the right tank on the car. 2: Install a new aftermarket sending unit and ensure that all the wiring is correct, including the grounding strap, solid state voltage limiter, and correctly operating gas gauge in the instrument cluster. 3: Install a Meter Match and calibrate its high and low points with the sending unit out of the tank. Make sure that the sender is grounded when you do this. The attached photos show the Meter Match velcroed to the upper left kick panel in the front seat, and the unit's circuit board. 4: Fill your tank, then figure out how many miles correspond to the 3/4 and 1/4 marks on your gas gauge. When you drive the car at a steady speeds and see the calculated mileage on your odometer, stop and calibrate these two spots with your Meter Match. Doing all of this will give you a very accurate and reliable gas gauge, and you'll no longer have to worry about running out of gas with the gauge showing 3/8 full like I did. Good luck!
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