Pppsssshhhhhhh

[John M]

Parked the 92 in the garage after the trek to drop my son off at school. Kicking back in the garage. Then out of now where I hear something that sounds like an air brake off a semi releasing pressure.

The sound....PPPPSSSHHHHHHHHHHHHHHHH.....fuel line blowing off the fuel rail


The smell....gas fumes instantly fill the garage.


The problem....building pressure in the fuel tank.


The solution.....don't know yet. Seems kind of intuitive that the vapor recovery system is somehow building pressure into the tank by not getting the vapors to the intake for combustion.

The vapor recovery system on a S4......well.......its gotten more complicated. In addition to the recovery tank in the trunk, we get blessed with a couple of check valves for outside air inlet and fume to manifold release. Then we also get a carbon washer cannister....hidden by the way up inside the passenger side wheel well....and yes....got to remove the wheel well liner to get at her. And also blessed with a ECU controlled solenoid that allows the washed fumes to travel from the carbon washer cannister to the intake.

So.....anyone have a clue as to who might be the likely culprit? Definitely got pressure in the tank....not a vacuum. No vent for venting out on this system. It has a vent that is check valved to deal with vaccuum on the tank. But fumes and pressure seems to have to go through the carbon cannister washer and then to the intake.

And BTW.....for all you whinny fuel pump guys......this thing was making a loud buzzing whine at the trunk vapor cannister that sounded like a fuel pump preparing to meet its maker. But a sure fired way to see if you have this problem....take the gas cap off while watching the gas tank. You will actually see it contract!

All suggestions appreciated.

Best Regards,
John M

[Pat's91]

Hi John, sounds like quite a mess. Which line blew off - supply from pump or return from regulator?

I can see how a faulty pressure regulator or blockage could cause high pressure in the pump discharge but the tank pressure should be controlled by 3 factors: vapor pressure of the gasoline at ambient temperature and vacuum created by dropping fuel level in the tank as it's used (there is a vacuum breaker valve to prevent high vacuum) and vapor recovery system.

I believe the vapor recovery carbon canister stores fumes when the car is stopped so pressure doesn't build up. Can you verify that the solenoid valve (on the PS fender) is opening after start-up to burn fumes from the cabon canister? I would also suspect that the check valve near the fuel vapor trap could be sticking closed.

Pat

[rbitzer]

Glad you didn't get a fire to put out! Good luck on that one, John. Did you have any fume problems prior to this problem or is this completely out of the blue?

We must love our cars to put up with all these crazy things breaking all the time!

Then again, how reliable are most 12-40 year old cars?!

[John M]

Hey Pat and Rob:

It wasn't really a mess. Mostly vapor but there was some gas on the back side of the hood. I had pulled in the garage and was kicking back in the garage watching the "Today Show" for a few minutes....then the PPPSSSHHHHHHHHHHHHH.

Supply side blew off the rail with band clamp intact. Didn't rupture the hose.....just backed it off the rail. Its back on now and nice and tight. I haven't repressurized the rail yet. Going to thoroughly check on this....as I fear as Rob....huge fire hazard.

I had some pre-symptoms. No fumes but I knew that the tank was building pressure. I had noticed an intermittent releasing pressure whine from the vapor seperator in the trunk. And upon opening the gas tank cap, the tank decompressed and shrunk....and released a rush of vapor around the cap.

I am going to check a few things:

1. I moved the vaccuum line tap for the recently installed cruise control from the solenoid that controls the vapor recovery.....and reinstalled it to the fuel pressure reg vaccuum line. Doubt that has anything to do with it....but thought worth a try.

2. And as Pat mentioned.....I am wondering about the check valve between the tank and the vapor seperator. A fault there could cause these symptoms.

3. I am also ....as Pat suggested.... see if I can test that solenoid that allows fumes to flow to the intake. Lines on that are so small...I don't see how that could handle that kind of pressure that would be required to blow off the fuel line.

My bet that the vapors are not even making it into the vapor seperator. That is the only way I can explain that kind of pressure in the tank. Not to mention that I just filled up the other night which likely would only make the condition worse.........less volume for the gas to expand.

I will let you guys know what I find. I am going after that check valve in the trunk first and then retest the car.

Thanks guys!

Best Regards,
John M

[John M]

Well.......I think this was much to do about a loose band clamp and little to do with the fuel vapor system.

After looking at this vapor system....and I must admit its the first time I have paid attention to it.......it doesn't seem likely that its the culprit for a few reasons.

A little description about the system:

This system has one hose running from the top of the gas tank near the filler hose. That hose runs to the lower inlet on the plastic vapor tank. The upper outlet from the vapor tank goes to the two valves that are low pressure fittings. One valve lets air in from the trunk on suction. The other valve releases fumes towards the carbon scrubber. Again all low pressure fittings without clamps. Hence, any significant pressure would blow these hoses off long before building up any significant pressure. Also the check valves are very low pressure fittings. You can easily blow through them. The humming/whining sound I heard was from the check valve releasing vapor towards the carbon scrubber.

So.....
I pulled the line off the tank and blew through it.
Check the outlet of the tank to this hose.
Blew through the check valves.
Blew through the vapor cannistor.
Lubricated the check valve between the vapor cannister and carbon scrubber.
Moved the cruise control vaccuum line from the "vapor" solenoid to the fuel pressure reg vaccuum line.

Still left to check the solenoid.....but as I have heard the check valve under operation with the engine running...the scrubber system must be running correctly.

Well, that's it. Like my engine check code 1223 that led me to do a bunch of preventative maintenance, the little clamp on the supply fuel line has inspired me to do the same to the fuel vapor recovery system. Oh well....such is Alfa ownership. As Rob said....it must be love!

Only thing that bothers me out of this little ordeal......Does the tank on everyone's Spider expand enough to visualize it shrinking upon removing the gas cap? I had the carpet out of the trunk after pulling the spare to refinish and noticed this on the 92. I haven't seen the same with the 78....but it runs a pump pressure at like 8 PSI...and for that matter never had the carpet out to notice.


Best Regards,
John M

[rbitzer]

Well being in NJ I never pump my own gas so how would I know about the Gas cap?!

But I am the anal gas-cap meister and only I know how to get the filler door closed properly so I do supervise. I do get a lot of air rushing out of the filler neck ( I think its rushing out...now I'm really curious ) whenever I remove the cap when the tank is low and/or its hot out.

Man, first Roadtrip with the splooshing, then John with the Pssssthing. I'm afraid to drive my car now...I'm afraid it'll make some other sound other than "clickity clack, vroom vroom", etc.

[John M]

Ha Ha Ha!

Rob, you are too funny. As long as it doesn't start going BAM BAM BAM BAM....you are good to go.

BTW, drove the car later on and all went well.

Best Regards,
John M