Strange Vacuum leak sound
 

I can't believe I'm posting this but I can't solve this problem. I just installed the UIM and started the car. It started on the first turn, after sitting for 4 weeks, the idle was steady at 800rpm, the PFC reads 457mmHG. Everything seems great, but when I'm standing over the UIM I can hear a LOUD hissing sound. I have checked everywhere for a vacuum leak but can't find it. Took the car for a spin and it boost to 18psi right away.

Is it possible the intakes can hiss that loud?

Hmmm. With an idle of 800 rpms you probably don't have a vacuum leak. maybe you installed a one way check valve backward and it's unplugged? Why did you have the UIM off? Are all block off plates (if you have any) sealed with a thin layer of silicone?

Sounds like you should just go around the UIM and torque down the bolts again. That's what i would do. It always happens to me, and i find one or two bolts could have used a bit more force to tighten them down correctly. Try that, then move to a possible vac leak.

-Mark

I had the UIM because I wanted to check that the 1600 secondary injectors were not leaking, but it seems the walpro pump is not holding the pressure after shut down like it used to. There are many post saying this is common. I will check the bolts again. I think that must be it because for the first time the turns of the wrench became unequal half way through the installation.

I will spray starting fluid on the UIM connection. I only sprayed around the injectors and blockoff plates before.