Fuel tank pressure

[lawrencedesigns]

Now that I have this 84 spyder on the road, I am noticing every time I open the fuel filler there is a rather substantial "whooosh" of pressure release.
I don't remember this happening years ago on my 74....
Any thoughts?

Keeth Lawrence
84 spyder

[Roadtrip]

Sounds like the vent system is clogged.

[Keven]

Yes, clogged tank vent system, clear it immediatley, cause it is straining your fuel pump. THe pressure can get so bad that the pump will start blowing fuses.

Do a search, someone else fixed this problem recently, and I recall a faulty one way valve somewhere in the system.

[Roadtrip]

I'm not positive on the 84s, but there's probably the vapor recovery tank inside the trunk with some small tubes coming out of it. On one of the tubes theres a small dead-ended looking valve. That valve allows air in (as fuel is used). If it's clogged up you can get negative pressure in the tank and cause fuel starvation and supply pump damage. In very damp freezing weather, it can freeze up.

[Gubi]

I'm having the exact same problem right now with positive fuel tank pressure on my '91. On the vent system, the separator and both check valves in the trunk are fine. On the other end, the solenoid into the plenum is functional if I put a battery onto it.

So either the solenoid isn't getting power or the carbon cannister is clogged up. Two questions:

1) Under what circumstances should the computer open up the vent system solenoid into the plenum? I'm assuming it opens when the engine is warmed up at higher RPM's..correct? I want to check it with a multimeter and see if it's getting voltage.

2) Anyone ever had a carbon cannister get plugged up? Seems like an odd thing to happen, but I suppose it's possible.

Thanks!

[Coqalfa]

Another possibility is the residual pressure developed by the "in-tank pump that precedes the filter. In the Bosch fuel injection systems, they require some residual start-up pressure in the system. This may be the source of your "whooooosh"!!
Regards, Brian

PS: Bosch does have a procedure for draining that pressure prior to replacing the filter.

[Gubi]

Quote:

Originally posted by Coqalfa Another possibility is the residual pressure developed by the "in-tank pump that precedes the filter. In the Bosch fuel injection systems, they require some residual start-up pressure in the system. This may be the source of your "whooooosh"!! Regards, Brian PS: Bosch does have a procedure for draining that pressure prior to replacing the filter.