I have a '99 4WD Blazer LT. I had the engine rebuilt 3 years ago. It seems to start fine, but when it gets warmed up and accelerating it it making a sound almost like a turbo. It whining quits when I let off the gas. I have also been loosing power going up hill and the RPMs have been getting higher. Any ideas?

 

Sounds like you have a vacuum leak going on. it'll whistle like a turbo. Look around at your vacuum lines etc until you find it.

 

did you figure out the problem my 91 is doing the same thing. And a vac leak would not cause the rpm to tack out. the whining noise is not like a vac leak or a bad alternator. sounds like a jet eng on start up

 

I did replace the vacuum hoses on the top by the engine and that didn't do it. It would rumble loudly on startup too. It turns out it was the catalytic converter. Whining and rumbling on start up gone. Got a local muffler guy to change it out for $200.

 

thanks for reply. most of the threads on this site have no follow ups. I had the same problem with my 91 4.3 4x4. after replacing the tranny and having the same prob as the old one i know it could not be the tranny. it turned out the be a clogged cat not fully clogged but enuff to make the tranny dog out on a load. the best was to fig out if you have this prob is to do a brake stand in reverse. if the tranny slips under load start with the cat. as soon as i cut it off the truck spun the tires no prob. HOPE this help someone.