Today I was tinkering under the hood and had the motor running. I actually did the water injection cleaning, which really smoothed out how the it was running afterwards, but after i let the car run for about 5 mins to do this procedure, I shut down the car, and took off the oil cap. I could hear a hissing sound like taking the cap off a soda bottle. What would cause this?

Some background info, I have converted to non-sequential and only have one line running to the filler neck. The one with the PCV valve in it. I checked to make sure it wasnt backwards and its not. Any ideas guys?

 

Do you still have A/C?

 

Depending on how soon after shutdown you removed the cap and heard that sound, it could be from one of the combustion chambers on the compression stroke that has'nt fired, bleeding down.

 

Nope A/C is gone along with the power steering.

 

It probably wasn't the cause of your problem in this case but your PCV plumbing is wrong. If only using one PCV line you want a plain hose extending from the oil filler to the primary turbo intake. The turbo intake is the only location that sees vacuum under all conditions so by doing this the sump has a vacuum applied anytime the engine is running.

If you use a PCV between the oil filler and manifold the PCV closes when under boost. That means whenever the engine is under boost you are not venting the sump which can lead to such things as blown out dipsticks, oil leaks or blown gaskets.

The '93 system has both lines in place. Perhaps the PCV valve was federally mandated at the time or something? I don't know. The only line you need is the one from the oil filler to the primary intake; no need for a PCV valve in this line.