Hiss under light throttle

1988 4.0 new rebuilt motor AT

Under light throttle, I can hear a hiss coming from the area around the fuel pressure regulator. I pulled the vacuum line to the FPR and listened and its there without vacuum.

Is this normal? I wonder if I need a new FPR.

You are going to have to wait for a renix expert to show up but I doubt it's the fpr. A hiss would usually be a vacuum leak.

I'm not understanding "It's there without vacuum".

Probably not unusual. Is it running okay otherwise?

Thanks for the responses.

After a 2nd round of listening, I think it may be a leak or hole in the heater hose running from the exhaust manifold to the airbox. It does sound like a vacuum leak. That would make sense because it's hard to pinpoint. Just sounds like it's coming from the front of the engine.

When I pull the vacuum line off the FPR and give it throttle, the hiss is still present. That's what I was trying to say.

I'm still trying to figure out why vacuum is low and gas mileage is poor.