[996TURBO]

From the "different cultures separated by a common language" department: :shock: :wink:

By ' gas tank' I presume you mean petrol/gasoline tank as distinct from lpg tank?

In no case is hissing sound normal. Have you tried the soap suds on all piping/tubing in that area?

Just occurred to me however that you may have a cracked/ chaffed air line....

The air line supplying the rear rhs airbag IIRC routes down the LH side of the car and then makes a LH turn and passes across to the other side between the top of the fuel tank and the body...devilishly difficult to get to .... it is prone to chaffing...I had the same problem 2 yrs ago so bought about 20 feet of 6mm tubing, duplicated the line attaching to old line with plastic zip ties. I encased the last 4' in some 1/2" ID plastic tubing I had spare to protect it from rubbing through.. never did find out where the old line was leaking from exactly but the new line solved the problem

hope this helps

I second that.

Have a look at your center exhaust.
Very often when they're dead, the heat melts 2 airlines (air tank and RHS airbag).
Location of the affected part of the airline is middle of the truck after rear wheels.
FIY, all the LH part of the airline from LH front spring is under a thermal protection until LH rearspring, then there's nothing to protect those 2 airlines.
I did experiment a new path for those 2 airlines : RH side of the car and directly to tank and RH spring. There's less chances to melt them with exhaust heat since the main part of the exhaust is LR side. I hidden those behind thermal panels for the cats.
No trouble since and easy to do.
That surely explain why your air tank is always drained.

 

[996TURBO]

Just a thought on a recent repair I had, check exhaust bend on top where it goes over axle.
One I had in had a long hole and it didnt even sound like a leaky exhaust, the heat built up where the air
pipes to tank and right rear bellows goes and softened them causing a hole in the tank supply pipe

All pipes replaced and now works well, replacing pipes is a b$%%&& if you wanna keep it original

+1 :thumb: at least you described it well and quickly