When cold, my fuel gauge indicates lower amount of fuel. If I drive the car for about ten to fifteen minutes, the indicator goes up a bit, probably by about 3 gallons or so more than when I first started the car. So, my question is, what causes this? And also, do you go by the cold reading or warm reading? Finally, my "fuel low" light comes on with about 3 gallons of gas left in the tank, is this normal? Do I need to clean out the gunk in the fuel tank, or anything else? Thanks in prior....

 

The little sensor ball thingee in the tank might be messed up. Also your tank could be dented. Its could be a myriad of things. Like my usual advice dealing with an RX7..........throw it away

 

Mine does that too, although I dont find it to be much of a problem. It might just take a min or two for the sensors to adjust or somthing. I go by the "warm" reading cause thats what's usually showing, but I never let my car go below 1/4 tank before filling up again.

 

The contacts on the sending unit in the tank are corroded or worn therefore sending mixed signals to the guage itself. If your **** call ray and order a new one if your a DIY'r pull the unit a lightly clean the contact points with non abrasive cleaner. About the fuel light and the 3 gallons of gas in the tank .......if the light came on when the tank was empty the would be a little defeatious wouldnt you say thats why mazda gave you a 3 gallon grace period to get to the nearest gas station. peace

 

ohhh hey by the way what part of san diego are you in i'm moving there in a couple months be cool if all the rotary guys down there could chill!

 

^^ I thought you were selling your FD when you moved? You know its not passing emisions in cali...

 

I am but that doesnt mean i wont ever be getting another..lol I am not scared of not passing emissions my cars worth more over here than there shipping it means I would have 3000 dollars in shipping costs?! Two times the price you bought your FC for just in shipping. Prob just get a real cheap roller up there and build it myself.

 

My light has always come on with 3 gallons left, which works out to about a 50 to 60 mile range.

 

The idiot light works off a thermistor on the tank unit. When it becomes uncovered with fuel it puts a ground on the idiot light circuit and turn the light on.

The gauge needle works off a float on a swinging arm. The swinging part at the top of the float assy acts like the wiper of a potentiometer. It makes contact with a wedge shaped coil and sends different resistances to the gauge.

JPG attached. Take one apart sometime and you'll readily see how it works. OR read the FSM, a section called BODY ELECTRICAL SYSTEM.

 

wrestler91, throw WHAT away? My vert? You be nuts to even suggest it. You must not have driven an RX7 vert.

boostd2rtr, I'm in La Jolla area and I haven't seen any other seven's since I moved here three months ago. I know there's a SD seven club somewhere, but I haven't been to their get-togethers yet. SD's a nice place but you're in Hawaii!!!

HAILERS, thanks and kudos for your wonderful insight and information. I've noticed since using the forum, that you are one of the rare few with consistently technically correct information, and without the attitude!!! Thank you very much.

 

Even the FSM fuel system test specs say to let the fuel gage "settle" for at least 30-40 seconds before looking at it. I'm not sure what the exact method of gauge actuation is, but I know the gauges are damped, and it just takes a while for the fuel gauge & such to get to their final point.

-=Russ=-

 

You think yours is bad, try driving an FD with some miles on it. My buddies 94 with 120k miles on the body has a really messed up gas gauge... it only gues 3/4 of the way up and drops really fast. He's already replaced the sending unit once.

 

Another thing I thought about. You said the gauge read more or less correct after the engine ran a while. Well, the way the fuel pump/rails/fpr work, is for fuel to continuously pass thru the rail and go back to the fuel tank. I figure this has to transfer some heat from the fuel rails on the engine to the tank making the fuel in the tank a bit warmer after a while.

So maybe part of the problem is the wiper and the pot are initialy cold and not making as good a contact with each other when cold, but as things heat up a touch in the tank they expand and make better contact???? Just a thought. I'm not talking hot, but warmer than they were when you started the engine.

And by the way, I've had my moments in responding to a couple of fine fellows on this forum. Unfortunatly the moderators deleted my responses to these fine little %$*#@$^&