WarpFactor

In my last car, the gas filler hose had a spring loaded flap which I assumed was to prevent gas from coming back up during spirited driving and to minimize fumes from being released. Also, when I unscrewed the gas cap, I heard a "PSSHT" sound of pressure releasing.

With the 8, the gas cap seems to fit very loosely. Half a turn and it's on or off. Definitely no "PSSHT" when you first open the cap. And there's no spring loaded flap either.

Is this normal for an 8? Is it anything to worry about? Could this be a source of poor mileage?

RXE16T

The pressure built up in your fuel tank is a result of how you've been driving and the variances in the atmospheric condition externally.

My 8 does not make the pressure releasing sound everytime I open the fuel tank, but it does make the noise occasionally, particularly after hard driving.

Pete

^^

JMD RX-8

The 8 uses a sligthly different fuel delivery system than the typical fuel injected car. On most cars, the fuel is pumped to the engine at full pressure constantly, and the unused fuel is then pumped through a return line back to the fuel tank. The 8 has no such return line. The fuel pressure is controlled by the PCM.

It is probably fair to say there's no comparing an 8 to other cars for a number of reasons, and he's just another. Unless fuel is sloshing out the gas cap, I wouldn't worry.

WarpFactor

Learn something new everyday...
Does this mean the 8's fuel pump is a 'variable speed' pump that pumps harder when you stomp on it? And pumps slower when you're just puttering along?

Gomez

Yes, it has two speeds. At a low rpm, there is a resistor that cuts the voltage to the pump and reduces it's output. At a rpm determined by the PCU, a fuel pump speed control relay energises and places a short across the resistor, allowing full battery voltage to the fuel pump....thereby increasing fuel output.

Gomez.

WarpFactor

If it's a two speed pump, that means it pumps fuel at two 'rates', right? If that's the case, and there's no fuel return line, does the rotary just burn the excess fuel that isn't required? Is THAT why it has such poor mileage? *Light bulb starting to glow dimly*

Gomez

I am regularly amazed at the differences in RX-8's across various countries. We have a spring loaded flap at the top of the filler neck on our Oz versions, and we have a different cap to the Yanks and you guys as well, it seems. We have to unscrew our cap 3 or 4 turns to get it off, and we don't have the Yankee version lanyard that attaches to it, either.

Gomez.

Rotary Titus

not to mention 250hp for JDM versions :p

Gomez

No, there is a fuel pressure regulator built into the pump. If there is a demand for more fuel than the pump is supplying, the relay will cut in and allow the higher flow rate. The pressure is controlled to 56psi, the regulator will dump pressure in excess of 56psi back into the tank. *Bulb extinguished, sorry* .

Gomez.

WarpFactor

I'm amazed too. I'm more accustomed to the spring loaded flap and the multi-turn gas cap as in my previous cars. This 1/2 turn cap just seems "cheap". Maybe I'll look into getting a different gas cap and see if I can find one that'll give me a few turns and tighten up nicer than the stock North American one.

And thanks Gomez for your explanation of the fuel delivery system. Sounds like you really know your stuff!

Gomez

Nah, I've done a few laps of this forum...and I've got a few reference texts that I enjoy looking through occasionally. This car is a real bag of tricks, I tell ya!

Gomez.