Last 3 times i've gone to fill my tank and i notice my fuel gauge is off by 1/4 tank...probably something with the sender....

any way to fix this without pulling out the tank?

 

Actually you dont have to pull out the tank to get the sender out. Remove the left rear tire. you should see a removeable pannel that was behind the wheel. Remove that. You'll now see the fuel level sening unit, its a 3 prong plug on 84-85 cars. Its on a metal plate with screwsd holding it in. Just remove the screws and replace the sender.

No need to drop the tank!

 

on my 80, when i fill up, i'd estimate the gauge reads somewhere between 2/3 and 3/4 full... kind of pisses me off, cause i have no clue where empty is (i can go by the trip meter, but that only works for highway driving... cause in town can be 10 or 16 for all i know, but hwy is usually 21-23)

 

Sounds easy enough, in theory.. But in the northeast, where the salt eats everything, those little screws holding in the sender always rust.. and when you try to remove them, the heads either snap off or they crumble.. Then you have to drain and drop the tank and take it to a gas tank shop to have it drilled out.... Good luck ...

 

Yeah, when I dropped my tank the fuel level sender was a big patch of rustola. Amazingly enough the tank was in perfect condition, and looks like it had been properly coated with gas tank rust paint

Dropping the tank isn't that big a deal. Run the car until you're pretty sure it's empty, or until it dies of lack of gas. (or if you are lucky enough to have one of the tanks with a drain plug, drain it... mine was welded in place).
- Open the fuel filler door and unscrew the three small screws holding the filler pipe in place
- Get under the tank. You can either use a jack and a piece of wood to hold it in place while you un-do the straps or do what I did - position yourself so that it "falls" down onto your chest. Doesn't sound like the safest thing, but it's really a light tank when it's totally empty. When full it would crush you.
- Undo the four bolts holding it in place, remove the straps, drop the tank enough to get at the lines on top
- Reach up and disconnect the lines. You should definitely label them, everybody forgets how theirs were hooked up.


And then you just remove the tank. It doesn't take long at all. Then you can take it to a gas tank shop. The local "Mr. Gas Tank" shop flushed the tank thoroughly/properly for me and installed the fuel level sender for like $30-40 cash. It's worth it to know that it's been installed and sealed properly, and that your tank has been purged of it's 20 years of crap buildup.

The connector for my fuel level sender was strangely missing. I think somebody replaced it at some point, and never bothered to acquire a new connector, just soldered the wires in place. So I went to a junkyard to find a connector. Rx7s in junkyards are few and far between here, but I found a 3-pronged connector under the engine-bay-fuse-box of a Mazda 323, which around here are a dime a dozen. Works perfectly. The wiring for the 3-pronged connector is in chapter13 of the heynes, the earlier 79-83 (I think) two pronged connector is in the actual fuel delivery chapter.

Jon

 

I've never looked at the sender on the rx-7, but I had an old Cougar years ago that had a similar problem. The connections had a bit of corrosion on them so I tried an emory board and light sandpaper, poliched them up and it read properly again. Easy fix on that one.

(Bizzaro- check your pm's- trying to find a date we could scoot up your way for a visit! )

 

Thats what I was thinking also. Hell, mine never worked (read roughly 1/8 tank when full) until I cleaned those connections off. I think the level sending unit is resistance based. more corrosion = more resistance.

 

thanx guys...hopefully this weekend will be clear enough to do this...

tom - I see no PM from you...it'd be nice to see you and your fam again

 

That is correct.
The sending unit should read approx. 3 ohms in the full position and approx. 110 ohms in the empty position. First ascertain that the sending unit has the proper resistance, then measure the resistance at the gauge itself to tell if there is increased resistance from the wiring. If you don't read any undue increase in resistance at the gauge, then the fault is probably with the gauge itself, which is kinda rare.

 

What if you get no resistance at all at the guage.. I have 7 volts reading at the connector, but when I put the ohmmeter on the two terminals of the sending unit... It reads nothing.. Am I checking it wrong?

 

Unplug the sending unit, then take a measurement.

 

Take a measurement at the connector, or at the unit.. I did both.. I have continuity at the connector.. Almost no resistance.. and no reading at the two prongs on the sending unit.

 

mine reads full when it is then when it gets to the half way mark it drops down to just below the e. it worked fine a few months ago, is that a sender isssue??

jb