Hissing noise/ vacuum leak?

On my 98 4.0 aw4 xj with ~115k miles on it makes a hissing/slight whining noise when Im light on the throttle. Between the engine and transmission there is a decent amount of fluid caked onto the bellhousing cover. I cant tell if the noise is coming from the cat (possibly clogged) or the transmission area. Sometimes it wont lock up and it'll slip when shifting or on the highway a little (not more than 5-10%).

Something else I noticed with my scangauge (im sure the numbers would be similar with vacuum gauge) is that my MAP goes from 6psi (normal) at idle to 3-4psia when throttle is slightly open. IMO thats not supposed to happen....it used to go to 10-12psia when in neutral and slight throttle opening. Do I have a bad map sensor, vacuum leak? Whatever it is makes me think the computer sees low pressure and uses less fuel possibly making it run lean? Im gonna run a compression test tomorrow and hopefully find some good numbers. Any thoughts? Thanks in advance.

Anyone?

Sounds like a vacuum hose or brake booster leak, follow the sound to the source.

are you sure the scan tool is reading map output and not translating it into vacuum already?

The tool reads map, when i hold it WOT when engine is off it shows 14.5psi usually. I'll keep trying to follow the noise. It sounds almost like its from the catalytic converter area.

BBeach said:

The tool reads map, when i hold it WOT when engine is off it shows 14.5psi usually. I'll keep trying to follow the noise. It sounds almost like its from the catalytic converter area.

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I had to turn the engine off a dozen times and run to listen for the leak source before it died (like 6-8 seconds) on mine just to find the leak. It turned out to be brand new POS hose I had replaced on a tubing connection. The ID of the new vac hose was defective and out of round so it had a tinnny leak. It was enough to cycle the doors on my AC dampers when I accelerated and make me think the AC blower was on the fritz.

I took a spray bottle on the vacuum lines, by the intake manifold gasket, around the tbody, etc and found nothing. When I rev in neutral you can hear the whine/sucking noise near the bellhousing area. Now that I think of it, maybe its an exhaust leak that's letting ambient air in and knockin the o2 sensor out of whack? Any ideas appreciated.

Bump. My transmission (auto) slips a little too when locked on the highway when this noise occurs it that helps narrow it down.