I went on a run today. The gauge went from 3/4 to 1/8 in about ten minutes. I found the closest gas station.

When I went to fill up the car, the pump kept shutting off as if it was full. I was able to get about 6 gallons in there. The gauge stayed at 1/8.

Stopped 30 miles later at another gas station, the pump also kept shutting off as if it was full and I only forced about 2 gallons. The gauge stayed at 1/8.

I've been premixing with Castor 927 4-8oz per fill up 8k miles ago after a rebuild.

Any ideas? I'm looking around online and I don't see symptoms quite like these.

 

Sounds like 2 separate problems. Odd that they would occur at the same time. The filling problem sounds like an obstruction in the fill line. Not sure what to do about that.

The gauge problem sounds like your float in the gas tank is stuck. That can be removed and inspected by pulling the fuel pump assembly. Its under the carpet on the drivers side of the rear deck. Pretty easy to remove. Not as easy to reinstall without getting it stuck. Good luck.

 

My guess would be the level sender or gauge needs investigating.
Tank is probably full.

To test that you can simply just fill the tank with the nozzle at the edge and "top-off" to see the true level.

 

When you say it won't take gas, is it spilling out or the pump just keep stopping? If the pump keep stopping then you have pressure built up in the tank, maybe check the relief valve, if it spills out then check you gauge sender.

 

The gauge dropping from 3/4 to 1/8 sounds to me like an issue with the float sensor. 6 gallons from 3/4 is full. Our tanks are 20 gallons so that sounds about right. Unless you sprung a serious leak you shouldn't be eating that much gas.

Matt

 

No way I lost 3/4 of tank to 1/8 going 75mph in ten minutes. Forcing the 8 gallons of gas to 3/4 ...1/2 a tank should mean its almost full...but its reading 1/8.

I got a suggestion that the pressure in the tank, that shuts off the pump every 6 or so seconds is the EVAP or fuel tank vent valve being stuck (thanks Jason Hite). Anyone else had issues with either of these parts?

I am thinking that somehow the float got stuck at the same time? Very weird. I saw some other posts that the ground on the fuel tree (????) might have come disconnected?

 

I think your tank is full. The gauge/float is faulty.

 

I think your tank is full as well. The fuel pump assembly needs to come out and be inspected.

 

Pull the fuel pump assembly and you'll certainly be able to determine if the tank is full. It sounds like the fuel level float is sticking or frozen in the empty position. Its all right there with the fuel pump.

 

 

I ended up taking it in. The shop it's at has not dropped the tank, but they are thinking the pressure issue is the vent vapor valve(s). They are plugged into the top of the tank.

I already did research on those over the weekend. Problem now, Mazda does not make them anymore. I saw Atkin has them. My mechanic found them on ebay for about $30. Any suggestions on where to find this part? I'm trying to get it to him ASAP as i have a track event in two weekends.

 

you do not need to drop the tank to inspect the assembly its very easy to check and to try Many things could cause this issue

the float might of sprung a leak and may be half filled with fuel thus never rising above 1/8

my first assembly had this issue

or maybe the float got dislodged and is hanging on by one of the hinges and thats why its reading lower than it should be .

Or the sensor itself may be faulty .

its rather easy to check aslong as you arent afraid of a little gasoline burn

 

I know the floater is in the assembly you can pull from the top of the tank through the trunk.

I have 2 issues, one is the floater the other is the car not taking gas.

The tank has to be dropped to replace the vent valves on top of the tank. Does anyone know where I can order those from other than Atkins?

 

How do you know the tank is not taking gas? Are you sure it's not just full?

Matt

 

We're truly trying to help so don't take this wrong. The vapor valve being clogged or inoperable for some reason is a very unusual event. Pulling the fuel pump assembly is a relatively easy exercise compared to dropping the fuel tank. If you or your mechanic have pulled the fuel pump assembly and can see the tank is not full, then I would proceed to evaluate the vapor valve. Until then, I would work under the premise that the tank is simply full (i.e., the reason it won't take anymore fuel) and that the float is not operating correctly for some reason. And I wouldn't let your mechanic talk me into work I do not need. I would make him show me the tank is no where near full of fuel.

 

I second what he said ^

 

There is a drain on the bottom of the tank... See how much is in there...

 

sigh,,, the car is not full. you must read my first post completely.

"The gauge went from 3/4 to 1/8 in about ten minutes. I found the closest gas station. " How could it be completely full when started at 3/4?

"Stopped 30 miles later at another gas station, the pump also kept shutting off as if it was full and I only forced about 2 gallons. The gauge stayed at 1/8."

how could it be completely full when i drove 30 miles?

 

Sigh...because your float is sticking making the gauge reading false, the tank was nearly full to begin with and you only burned about 2 gallons driving 30 miles?

 

And to confirm the level you can pull the pump hanger and have a looksey

Does your shop know anything about rotaries? Or cars?

 

^^^

Sigh...drove 30 miles and burned two gallons of gas. Sounds like the average 17mpg all rx7's do.

It's been repeated like 14 times already but I'll go ahead and break out the club for this pony.

Pull the pump/float unit. Observe that you're tank is actually full, and test the float sensor.

Matt

 

Come on guys, its clear that the tank isnt taking gas normally. That is an issue that needs to be resolved.

 

were assuming the fuel gauge was working when it was at 3/4, then it dropped to 1/8th of a tank so you decided to get gas. FD's have 20 gallon tanks so 6 gallons is roughly a 1/4 tank. That is why everyone believes your tank to be full.

 

Lots of heavy breathing in this thread.

 

Its incredibly easy to:

A. Lift up the trunk carpet.

B. See fuel tank inspection cover held on with a few small screws.

C. Remove tin plate inspection cover. See and touch the vent valves with your own hands at this point!

D. Unbolt and slide out the fuel pump with only a few bolts! Look into the tank. Gaze deeply into it, hear its secrets. See its fuel level firsthand. Much wow. Many good.

Time taken: 15 to 25 minutes at home.
Can't believe it needs to go any further than that for ^&** %^&*.