It wasn't leaking that much. Just enough to fail my commissioning test.

I spoke to the Aeroforce tech about it. First he advised me to cut off the "spark plug" metal seal. That just made it worse. He told me it was an NPT male thread but it does not fit tight into a female NPT coupling.

I plan on using my A/F gauge to let me know if I have enough fuel pressure.

An O ring seal would be more appropriate.[/list]

Thread compound will never seal straight threads. Use an o-ring.

Now that I have the gauge back in I like it better back under the hood where it is more useful for tuning the fuel pressure regulator.

I will try the O-ring with the water injection system pressure.

Here is a better pic of the adapter and sensor. You can see the sealing ring.