30 replies to this topic

[Dylan]

_{From http://www.drive.sub..._FuelSystem.htm}

When thinking about high-tech Subaru features, the fuel tank probably isn't the first component that comes to mind. However, beyond its most basic role of storing and supplying fuel to your vehicle's engine, the Subaru fuel tank features sophisticated engineering designed to keep you and your passengers safe.


The most critical task we face when designing a fuel tank is making it safe," says Yoshiaki Oyamada of the Subaru Engineering Division. "Gasoline is highly flammable when it evaporates, so we must take extra precautions and pay scrupulous attention to the tank's design."




How dangerous is gasoline vapor? We've all seen news reports where cars and trucks have accidentally caught fire while receiving fuel at gas stations. On vehicles with poorly engineered fuel systems, it's possible for evaporated gasoline inside the fuel tank to come rushing out when the fuel tank cap is opened. When air is dry, even a tiny spark of static electricity transmitted by the person opening the cap can ignite this flammable vapor and cause a fire.

"To prevent static-induced fires, the fuel filler lid of Subaru vehicles opens just halfway when you unlock it by pulling the lid release lever inside the car," says Oyamada.

Because the lid only partially opens, the person refueling the car has to open it the rest of the way by hand. Any static electricity transmitted dissipates through the lid, before the fuel tank cap is opened – eliminating the risk of fire. This fire prevention system is a hallmark of the Subaru commitment to safety.




Fuel and fuel vapors move from and to the fuel tank through three lines – one for sending fuel to the engine, one for returning the fuel unused by the engine back to the fuel tank and one for handling evaporative gas (fuel vapors) from within the fuel tank.

Air pressure and increased temperatures cause gasoline to evaporate inside the fuel tank. When evaporative gas is produced, the volume inside the tank increases and the vapor must be released. The vapor is drawn into a charcoal canister to store the hydrocarbons, which are hazardous to health and destructive to the environment.

At the appropriate time, the Electronic Control Module (ECM) on-board computer instructs the solenoid purge valve to open and the hydrocarbons stored in the canister are released to the engine, mixed with intake gas and used as fuel. So recycling the hydrocarbons collected by the canister actually improves your vehicle's fuel consumption while protecting the environment.





When designing a new Subaru model, the fuel system often endures several design changes to accommodate space requirements for other components. For instance, as a result of the all-wheel drive system used on all Subaru models, the Legacy fuel tank features a unique, saddle-shaped design to accommodate the drive shaft for the rear wheels. A state-of-the-art jet pump transfers fuel from one side of the tank to the other to keep the fuel running efficiently though the system.

"Whatever the request, our tank engineers employ the most advanced technology and do whatever it takes to ensure a safe, pleasurable driving experience," explains Oyamada. "It is our challenge – and our chance to showcase our skills."

[legacy rsk]

interesting thanls dylan

[Alex]

lol more things to break!

[Dylan]

For anyone that is interested, I am currently experimenting with the fact that not having the charcoal canister in place can result in inaccurate fuel level readouts. I have often wondered the purpose of that canister, and it seems to have more of a purpose than first thought (going from that diagram). I am also interested to see if it results in any other symptoms, i.e. missing, lean / detonation etc.. I will advise if I notice any difference after re-fitting it tonight.

[Soop]

Its there as an emmisions thing. HAI TRISTAN.

[Dylan]

Yeah. Do you know much about how the fuel level sender is, is it simply a floating type device that sends back a voltage or something to give information on fuel tank level? If this canister is not in place, I think the fuel tank may lose its vacuum and have a feeling this may affect fuel level readings, to give you an example: my fuel light comes on with 1/4 of a tank, and when I fill it full its WAY over full! Thoughts on that Pauly?

[Soop]

I'm not sure how they do it on the Subaru's. I know on the old holdens it was just a float, that sent voltage to a guage. I'd assume that it would be similar in the Subaru. I think its more probable, that your guage is dead.

[Dylan]

Hm, interesting. I will see how it goes. I suspect my speedo is out by as much as 12km/h at speeds over 80km/h or so, I have heard mixed reports they are meant to be out by a bit but this seems a bit extreme. Anyone know about cluster re-calibration?

[Scuba-Roo]

i thought the fuel canister was there to stop/help fuel expanding in heat etc so it didnt flood your engine. jaycar have kits that you can adjust your speedo reading, but you need to have an electri speedo, not a cable one.

[alexGT]

dylan, get hold of a gps, they are accurate to less than 1kph. get to a constant speed and check it out. with my 18s my speedo is dead accurate.

[Dylan]

Yeah, I've got the N96 that has a GPS although I am a bit suspicious of its accuracy. Hm, perhaps an excuse for me to upgrade to 18's then Thanks Alex

[Shiv]

If you think your speedo is out by that much, it would def be worth getting the speedo recalibrated. Although I've no idea about that sort of thing, whether its expensive and that... FYI - when my GPS tells me I'm doing 110km/h, my speedo reads 114km/h, and we run the same rims. I'm finally putting on the 17's tomorrow. Will be interesting to see how much that changes it....

[Dylan]

Hmm. I have _NO_ idea about how the speedo works, none at all. Interestingly enough though, an ECU data scanner I've borrowed from Jonno (Jock) reports the SAME speed as my speedo is displaying, yet GPS displays differently and I've had mates complain that I drive slow at times, too. Can anyone explain or provide any information and insight in to this phenomenon? Why could my speed be out? Factory rims, cluster, different engine + gearbox though, factory tyre size.

[Soop]

voltage issue from a sensor/ecu?

[Scuba-Roo]

wouldnt the v2 wrx gearbox be calibrated for v2 wrx sized rim+tyres?

[B4TT]

Get your Speedo calibrated dude, means taking your cluster out and sending it away. I have only seen a few that have needed doing but it can happen. Last one I seen done though was on an SLR5000 man normal day to day GPS isnt accurate to within a few K's.. take it with a grain of salt. Carbon Canister shouldn't affect the fuel level reading at all, its an emissions thing. Paul is right, the subaru's use a float and sender unit that moves up and down and sends a low voltage signal.

[Dylan]

wouldnt the v2 wrx gearbox be calibrated for v2 wrx sized rim+tyres?

Hmm possible - I am not sure. I'd assume v2 had 205/55/16 though?

Get your Speedo calibrated dude, means taking your cluster out and sending it away. I have only seen a few that have needed doing but it can happen. Last one I seen done though was on an SLR5000
man normal day to day GPS isnt accurate to within a few K's.. take it with a grain of salt.
Carbon Canister shouldn't affect the fuel level reading at all, its an emissions thing. Paul is right, the subaru's use a float and sender unit that moves up and down and sends a low voltage signal.

Hmm. Why would ECU report same speed as speedo is reporting then?

[B4TT]

maybe it gets its speed information from the cluster? I dunno to be honest.

[Soop]

good chance there is an issue with the wiring/sensors PRE ECU. The ECU would send the info to the guage not the other way around. EDIT: Consulted the Oricle at work. We reckon the issue is, you've gone from a 3.9:1 final drive, to a 4.11:1 final drive with the WRX driveline. The variation in the reading will be due to the way the speed is messured in the gearbox. It is generally taken from the output side of the gearbox. So with the shorter ratio gearing, the output is spinning faster to achive the same speed. Remedy? replace the speedo drive in the gearbox or use larger wheels.

[Dylan]

Hm, alright thanks guys. Will do some digging up, my knowledge on HOW the speed is determined is nil so need to work this one out

Edit: Posted up some information on this subject.