83sc hissing sound

mack6820 · 05-15-2011, 03:05 PM

Hey guys. My 3.0 has a loud hissing sound only under load and at 1/3 to 1/2 throttle. Sounds like a turbo wastegate. I can't figure out where its coming from. It ONLY does it while driving(under load). So I jacked it up, put it in gear and ran it on jacks under load and it still doesnt do it. Sprayed the entire CIS with throttle body cleaner with no luck in idle changes. Put a flashlight inside the boot to check for cracks. Also screwed the idle screw all the way in and it stayed running.
Any suggestions?

Joe Bob · Joe Bob's Garage

Check your head studs....

Bob Kontak · Bob Kontak's Garage

You must have a vacuum leak but I have never heard hissing.

You said you sprayed the entire CIS. Does that include the base of the intake runners where they meet the head. Check the airbox closely. I have had the brass tube come out of the back of the throttle body and you can't get to that with the spray easily. However, the car would not run at all. Also, the brake booster hose can suck air.

Odd that there is a hissing noise as vacuum decreases with open throttle.

mack6820 · 05-15-2011, 04:47 PM

Its driving me crazy that I can't duplicate it unless I'm driving. How difficult is it to check the head studs?

Joe Bob · Joe Bob's Garage

When the headstuds on mine went the sound was like playing cards in the spokes of a bicycle...I could see how it sounded or could sound like hissing.

Pull the valve covers, you'll find loose nuts and/or busted ones rattling around on the inside.

When was the last time you adjusted your valves?

fastfredracing · 05-15-2011, 04:55 PM

Catalyst plugged? Under load , there is little vacum. so I doubt that is it Vacum leaks are usually loudest at idle

mack6820 · 05-15-2011, 05:00 PM

Its definitly a hissing sound and not a rattle. I am due for a valve adjustment. The catalyst has been gutted by the PO. I tried to hook up my gopro camera and drove it but the sound didnt come clear enough to post. I'll try again when my batteries charge.

911Freak · 05-15-2011, 05:15 PM

Quote:

Originally Posted by Joe Bob

Check your head studs....

+1 This is what came to mind 1st for me as well... Let's hope it isn't the case

Is the engine otherwise running smoothly? Any drop of in performance whatsoever?

Is it idling smoothly at correct rpm without hunting?

Sound different when engine is warm or cold?

If there isn't a drop of in performance, idles correctly and otherwise is running in normal good condition I'd also suggest taking a look at the head studs, there's only so many things it could be...

Good luck

Bob Kontak · Bob Kontak's Garage

See post #11

80SC Engine Noise Question

rootmatt · 05-16-2011, 12:44 AM

It is hard to describe noises. Sorry, I haven't heard a turbo wastegate from in the car. Could the sound of a loose pinion bearing race in the tranny, rotating under load, be described as a hiss? Hope not.

Matt

mack6820 · 05-16-2011, 08:50 AM

Quote:

Originally Posted by 911Freak

+Is the engine otherwise running smoothly? Any drop of in performance whatsoever?

Is it idling smoothly at correct rpm without hunting?

Sound different when engine is warm or cold?

If there isn't a drop of in performance, idles correctly and otherwise is running in normal good condition I'd also suggest taking a look at the head studs, there's only so many things it could be...

Good luck

The car runs great, idles perfectly, strong performer, hot and cold. It does it at ANY RPM with the throttle approx 1/3 pressed. It is definitly an air leak sound and not a rattle or tapping sound.