LETS LAY THIS ONE DOWN TO REST
TPI
Mine makes a nice hiss sound. People say something may be blocked (fuel canister). Also, does this mean my fuel pump is working ok? Cause I'm changing it out to combat a hesitation problem.

POS

 

My cap does the same thing. There are times, depending how long I have drove the car, and how empty the tank is, that once the cap is unscrewed, the pressure will blow the cap onto the ground. I have heard some cars are suppose to do this. This is b/c they have a pressureized fuel return system. Or something to that effect. I'm sure I am not totaly on base here, so someone please set me straight.



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Joshua Johnston
1991 Z-28
Flowmaster
K&N
305 / 5spd. (Temporary)

 

The hissing sound is normal as far as i know. I wouldn't worry about it too much. Mine does it, yours does and i'm sure everybody elses does, about the tank being emptier than others, i think that is true, mine has more pressure the lower the tank is the more the pressure.


Brendan

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1987 IROC-Z L98,SuperRam,EB 6085's,LPE 219/219 Roller, Crane 1.6RR, EB TPI Base, 58mm TB, ADS 24#, AFPR, K&N, EB TES, Catco Cat, 3" Borla Cat-Back, Accel cap,rotor,distro/other crap, MSD 6AL, MSD Blaster 3, Aluminum DS, 94 Disk Rear, Adjustable Valve, Precision 3.73 Gears, Sub-Frame Connectors, Hotchkis Lower Control Arms, KYB Shocks/Struts, Suspension Techniques Lowering Springs, Polyurethan Bushings all over the place, Moog Upper/Lower Ball joints and Tie Rods ends/Idler Arm,

To see the ROC, Check out the webpage Here

 

Don't worry about it. It is normal. My IROC does it everytime. I work for the NJ State Inspection Program. It is mandatory that we check the EVAP system and pressurize the gas caps on all the cars. Just about all the new cars do it too!!!

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Rob Kowalski
85 IROC, 305 TPI, JET AFPR - 45 PSI, B&M Megashifter, B&M Shift Kit, 3.42 gears, SLP Airfoil, SLP 1 5/8 headers and cat back system, gutted cat, gutted airbox, MAF screens removed, K&N, more to come!!

 

you work for NJ State Inspection? you EVIL EVIL person

when i take off my cap it releases pressure as well i guess its normal

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"What does not kill us only makes us stronger"

Tony

 

This is a little off topic, but I have a nice job at Caterpillar. Every job has its little perks. Police can speed a little more, not use turn signals all the time, same w/ fireman, EMT's. Computer programmers(at least the ones I know) travel for next to nothing, free rental cars. The list goes on....BUT a State Inspection Job would totaly kick *** , at least for a car guy. If i could make the money I make now at an Inspection Job, I would never talk bad about life anymore.



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Joshua Johnston
1991 Z-28
Flowmaster
K&N
305 / 5spd. (Temporary)

 

The tank pressurizing is a normal condition to some extent. It is caused by the fuel system being a sealed system (ie not vented to the atmosphere). This is because of environmental laws that prohibit vented fuel systems. With the sealed system, the cars engine is used to burn the fuel vapor that normally would get vented to the atmosphere. This is used because by running the vapors through the engine, they are turned into 'daisies and roses' when they come out the exhaust because of the chemical reaction that takes place in the catalytic converter. The tank can OVER pressurize or form a vacuum if the EVAP system has a malfunction and never lets the fuel vapors out or doesn't let air into the tank to replace the space that the fuel leaves when it is used up. Having seen both of these conditions first hand - and having seen them take out the fuel pump, I remove the EVAP canister and its components and than allow my tank to vent to the atmosphere - it's easier on the pump - and highly illegal...hehe......

Laterzzzzzzzzzzzzzzzzzzzzzzz

 

My 84 maro & 87 bird both hiss too. Even tho this is pretty much 'normal' from just about all 3rd gens (I assume and, probably many other cars) it really isn't supposed to do that. There's a valve in the back where all the lines for the tank connect from the sender to the lines that run down the car frame underneath called a ventilator. From what I was explained about this is it's a one way valve designed to let excess pressure bleed off from the tank while the car has been running (heat from the exhaust supposedly is the culprit of this pressure) or overly hot days and over time the valve ceases to function the way it should. There's no harm in letting it hiss away,, but it wasn't in the original design.




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My Firebird It Lives Again!!(Sorta)
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Part Diagrams

-It's always the last one

 

I said it before and I say it again; some peple in this board drown in a glass of water.
The pressure is caused by the exhaust system being right below the fuel tank. No matter how much insulation you put in between the two, the exhaust will always heat up the fuel inside the tank, thus turning it into a pressure cooker. GM knew this and put a relive valve to vent excess pressure.
Rick

 

Nope, GM did not put a relief valve in the system that vents the tank into the atmosphere because that would not be legal. The fuel system LEGALLY HAS TO BE SEALED!! The valve that he is refering to is a relief valve of sorts, but it is a one-way valve to let fresh air IN to the tank when needed (ie when the fuel gets used up).

Laterzzzzzzzzzzzzzzzzzzzzzzzzzz

GO ARMY

[This message has been edited by Matt87GTA (edited April 18, 2001).]

 

If you don't mind the curiosity,,



Since I'm not much on emission laws (and mine's not exactly hooked up just yet),, wouldn't this (pic/red arrow) be considered open to vent into the atmosphere?

[This message has been edited by deadbird (edited April 17, 2001).]

 

Nice pic. Good detail. And yes, that is a vent, but, it is an INTAKE.... when you purge the cannister, the air going thru it has to come from somewhere.

 

How can you purge the canister? Should I clean mine? ... it's orignial I'm sure. Can I remove it and blow compressed air through it? or use water?

Thanks

 

The car (ECM) purges the canister itself while the engine is running at different times like on the freeway. That filter on the bottom of the canister can be changed if you want to. I dunno the p/n off hand but any GM dealer should be able to get you a new filter. I say, if your states' emission laws aren't that strict and they won't notice it missing, remove the whole thing and just leave the purge solenoid hooked up and hidden somewhere so the ECM still thinks that everything is OK. That way you will have all the benifits of a vented fuel tank, (see my fuel pump issues above) and no DTC's will be set for a missing EVAP purge solenoid. (That's what I did and I have no probs with the hissing noise or any DTCs )

my $.02

Laterzzzzzzzzzzzzzzzzzzzzzzzz

 

So what did you do with the two hoses and the electrical connectors specifically?

 

You don't need to leave the soilnoid hooked up. Actually you can remove everthing smog(air and cannister) except for EGR w/o the computer throwing a code. and there's a way around defeating egr through prom work.

 

I plugged the vacuum port on the TB and the hardened line that comes from the EGR, removed all vacuum hoses associated with the canister. I than routed a rubber hose off of the fuel tank vent line (the metal one that is fastened to the 'frame' of the car) up through the core support into the bumper cover area where little if any water will be able to get into it (I don't drive my car in the rain if I can help it). I than connected the Solenoid to the wires and tucked into the core support where it can't be seen by where the pop-up mounts to it. And that's about it. It really cleans the underhood area up well and gives a good access path to the inner fenderwell opening that routes cold air into the underhood area for my air intake system (poor mans cold air setup ).

Sorry, no pics........yet......

Laterzzzzzzzzzzzzzzzzzzzzzzzzzz

[This message has been edited by Matt87GTA (edited April 18, 2001).]

 

Ok, let me dispell some of these myths.

1) The "ventilator" does not act as a pressure relief. It lets air INTO the tank. As fuel leaves, something MUST displace the missing fuel or the tank would collapse, so air is allowed to enter.

2) The EVAP canister is also not a "vent", it is a canister of activated charcoal for the purpose of collecting fuel vapors to be sucked into the intake during a "purge cycle". The bottom is open, and filtered, to allow fresh air to be drawn across the charcoal and carry the fuel vapors (Hydrocarbons) into the intake to be burned.

3)It may be possible that the exhaust is heating the tank, but the majority of the heat is caused by the fuel returning from the fuel rail. Remember, the fuel rail is mounted to an intake that easily sees 200*F, and then is pumped back into a tank of fuel thats about 70*, and the fuel boils off. If you have ever undone a fuel line on a hot engine, you know this by heart.

4)The EVAP system does burn off vapors from the tank, and will help to alleviate some of the tank pressure, but on hot days, it can easily be overloaded, causing tank pressure.

5) The computer is a "dumb" computer. It does not check circuit integrity or verify the action has been carried out like OBDII computers. You can unplug the EVAP and AIR systems, and the computer will never know.

I hope this clears the air. (no pun intended)

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If you live in Southeastern US, check us out!
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GM Master Tech
ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey,
22# injectors,
Whatever chip I feel like burning,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
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-->14.97 @ 94.9 MPH<--

'97 Bonneville SSE

 

Hey GMTech, isn't that what I said? (sans the solenoid thing - I didn't want to try it without the solenoid and get a DTC so I just left it on)

Laterzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz

Ever heard of ASEP??????

 

Yeah, just trying to catagorize all of it.


Yes, the ASEP/BSEP programs are very good if you are interested in the field. I did not do it when I started out, but I work w/ some that did.

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If you live in Southeastern US, check us out!
South East Thirdgen

GM Master Tech
ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey,
22# injectors,
Whatever chip I feel like burning,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
-->14.97 @ 94.9 MPH<--

'97 Bonneville SSE

 

I graduated from ASEP in 1997, wrenched at Friendly Chevrolet for a few years and now I am back in school for Engineering. I agree, I learned a TON in ASEP plus I got about $10K worth of GM manuals for free.

 

Another ASEP graduate here in Md. back in 1995

I used it to get paid more at the dealer.. 23 STG classes and an A.A degree later, and I went from 14.00 an hour to 21.50.

Went back to school for a couple years ago to become a Network Engineer.

 

Hmmmm.....sounds kinda familiar Kevin.....'cept I'm going for Computer and Electrical Engineering.

 

posted by F22Raptor
Looks like someone has just drowned them self

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"Powertuned"
83Z28 w/ 434 SBC
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