I recently bought a non running 95 Z28 A4 Convertible, 108,000 miles. I replaced the OPTI and got it running. The car seems to idle fine and ran ok (but not great) at higher RPMs when I initially took it for a test drive. After it fully warmed up it started "surging" so I took it back to my shop. I hooked up a fuel pressure guage and restarted it. Fuel pressure was good at idle. I tried revving it up to see how that would affect the fuel pressure. When I opened up the throttle it made a LOUD squealing noise that sounded like it was coming from the top/rear of the engine. It sounds a lot like a squealing belt but I am certain it is not the belt making the noise.

What is there at the top/rear of the engine that could be making this noise? I have worked on a lot of older engines but the LT1 and Fuel Injection is new to me. Could the injectors make a noise like this? Based upon the way the engine was running I thought it could be a vacuum leak but I have never heard a vacuum leak that was anywhere near this loud before. Could it be a vacuum leak?

Thanks, Joel

PS. I don't (yet) have a scan tool.

Once my thermostat housing was leaking a very tiny bit, and the small hole in the gasket was shaped to the point where it would make a loud wine. Maybe take a look at your hoses and gaskets - look for small leaks.

My recently aquired 66 GTO made a similar sound, only I likened it to more of a whistle sound. And it was in fact a vacuum leak. I don't know exactly which line was leaking because I replaced and tightened them all at the same time. No more whistle.

Take a piece of small diameter hose, and stick one end near your ear, the other end dance near where you think the noise is coming from... if it's wind you'll hear it..

John