Fuel gauge not working correctly
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Joined: May 2008
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From: Seattle, Wa
Fuel gauge not working correctly
Ok, once again, I just got an 87 gxl about a week ago. Since I got it, the fuel gauge doesn't work correctly. When the tank is full it reads it, but when I get to 3/4 of a tank it goes to empty. Now, what I'm wondering is, is the float/sending unit integral with the fuel pump, or is it separate? Also, I have been to Schuck's and they don't have a listing for it. Do I need to special order one from the dealer?
HAILERS
Joined: May 2001
Posts: 20,563
Likes: 27
From: FORT WORTH, TEXAS,USA
Go to Mazdatrix's site and you'll find the sender unit for sale. Your's is shot. You remove the fuel pump from the tank and then just replace the sender that is attached to the pump.
See the FSM on how to determine if the sender or the gauge is bad. There is a procedure there. But it is the sender that is bad.
See the FSM on how to determine if the sender or the gauge is bad. There is a procedure there. But it is the sender that is bad.
I wish I was driving!
Joined: Dec 2001
Posts: 5,241
Likes: 84
From: BC, Canada
Here is what happens:
The stock sending unit is basically just a plastic float on a pivotting arm. As the arm moves up and down, it wipes across a coil of wire. All wire has a specific resistance, and the gauge responds to difference resistance values. This wiper arm shorts out some of the coils, and lowers the resistance of the total coil to effectively change the resistance.
Over the years, the wiper arm wears into the coil of wire, and eventually, it wears right through. At this point, the coil has infinite resistance since there is no connection.
The wiper arm will still short the coil in the upper portion of the gauge, but as crosses the open in the coil, the unit will stop working.
The only option is to replace the sending unit, which is bolted as a separate unit to the fuel pump assembly.
If you'd like, I have a new stock sending unit laying around you can buy.
The stock sending unit is basically just a plastic float on a pivotting arm. As the arm moves up and down, it wipes across a coil of wire. All wire has a specific resistance, and the gauge responds to difference resistance values. This wiper arm shorts out some of the coils, and lowers the resistance of the total coil to effectively change the resistance.
Over the years, the wiper arm wears into the coil of wire, and eventually, it wears right through. At this point, the coil has infinite resistance since there is no connection.
The wiper arm will still short the coil in the upper portion of the gauge, but as crosses the open in the coil, the unit will stop working.
The only option is to replace the sending unit, which is bolted as a separate unit to the fuel pump assembly.
If you'd like, I have a new stock sending unit laying around you can buy.
-assuming the fuel pump/sending unit have never been removed/replaced-
Be prepared to fight the retaining screws on the mounting plate...in fact, just plan on replacing them with some nice ss hex or allen heads.
Also, as long as you're in there (and to avoid going back in anytime soon) you might consider going ahead and replacing the fuel pump and sock along with the sending unit.
Think of it as preventive maintenance.
Be prepared to fight the retaining screws on the mounting plate...in fact, just plan on replacing them with some nice ss hex or allen heads.
Also, as long as you're in there (and to avoid going back in anytime soon) you might consider going ahead and replacing the fuel pump and sock along with the sending unit.
Think of it as preventive maintenance.
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