miasmicmonky

iTrader: (1)

I have an 83 LE with an odometer that stopped working at 206k miles. The problem i have with that is also the fuel gauge doesn't work once it gets below half. I am curious if anybody has any ideas as to what to check out first. If my odometer worked, that would be great because I would just go by mileage. XD I haven't been daring enough to test whether the low gas light works or not.

Thanks in advance.

t_g_farrell

iTrader: (1)

So the odometer is just drivin by a cable that connects to the speedo from the tranny. You
should check that its connected at both ends and spins freely. Easy way is to disconnect at the
tranny and put drill on slow and see what happens. If it doesn't spin freely you can pull the
cable out, disconnect at the speedo and clean and lightly lub the casing and then clean the cable
and insert back in.

The gauges works by the value of the resistance. As this setup ages the resistance goes up
and that causes the gauge to be off, sometimes by a lot. This fix is to get the connections
cleaned up and make sure the resistance is where it should be. The FSM has the values the
gauge should see. One issue is that the gauge gets its ground by its attachment to the tank
via the body of the sender in the attachment. You can jump a wire from the body of the
sender to one of the attachments bolts on the tank to get a better ground. I had to do that
to ultimately fix mine.

speedracer_not

"You can jump a wire from the body of the
sender to one of the attachments bolts on the tank to get a better ground"

So I have to drop the gas tank??

erick31876

iTrader: (8)

If i remember correctly,you can get to the sending unit by removing the plastic cover/wheel liner on the left rear wheel well

RXTbone

Regarding the gas gauge - before tearing anything apart - might try a couple $4 bottles of Techron (brand specific) in a couple tanks of gas. Cheap fuel is bad fuel and gums up the sensor. I thought it was a suspect recommendation - but so far it's helped gas gauges on two of my older model cars.

mazdaverx713b

iTrader: (91)

I would remove the gas tank to remove the sender. The screws that secure the sender to the tank can be a bear to remove due to rust and will easily round. Sometimes needle nose vice grips are needed and in some extreme cases, the screw heads must be drilled.

Now with that said, the sender needs to be removed and a resistance check must be performed on the sender in a few locations. chances are, its out of spec. The sender is just a bar that moves over wound wire. A pretty archaic setup but it does work well. The bar wears the winding and the resistance increases and the gauge becomes inaccurate or stops working all together. I would just plan on replacing the sender. New ones are available from Mazda still luckily. If you would like I'll post up the test procedure with a picture from the FSM showing the resistance values.

As far as the odometer not working, if the speedometer works properly, then the cable is secure at the trans and at the speedometer. The odometer itself most likely has an issue like a bad gear. The gear commonly breaks on Porsche's from the 80's. I have replaced several over the years on my 944's. As far as I know, a replacement odometer gear is not available from Mazda and a used speedometer must be purchased and installed.

speedracer_not

my gas gauge reads full to 1/2 full, and then empty. It would be great if I could remove the rubber thing under the spare tiire, and clean some contacts to fix it. Things that need fixing keep increasing....speedo cable, door panels, antifreeze change, stain wood for the consul switches

DivinDriver

iTrader: (15)

There is a test procedure for the fuel gauge/sender in the FSM; essentially it's:
Jack the car, remove left rear wheel, remove plastic panel at rear of wheel well to expose sender and it's cable.
Disconnect the cable and substitute some known-value resistors to check gauge response.
If gauge response is correct, then sender is faulty - - either gummed or failed open.
Based on your description, it's most likely your problem is in the sender, since your gauge is able to display both full and empty.
Most probably the wire coil in the gauge has worn thru near the middle, so once the float in the tank crosses the worn spot, the circuit fails open and no current gets to the gauge, causing it to read "empty".

Sometimes you can solder-bridge the bad spot in the coil.

There's a thread in the archives I wrote up years ago that shows the internals of the sender in good detail.

https://www.rx7club.com/1st-gen-arch...sender-786986/

t_g_farrell

iTrader: (1)

Whoa guys! It may just be a ground issue between the internal sensor and the tank. Thats
all mine was. It wasn't worn down or broken on the variable resistence coil.

Do like Divin suggest to make sure your guage is working correctly.

Another quick test is to take a copper wire and hold is to the outer base of the sender and
then take the other end and push against the bolts on the sender or the tank and see if the
reading works better. Thats the work around I ended up doing.