Squeal at high revs

[Dash65]

Sorry if this has been posted before...I didn't find any that exactly matched my situation.
I just got my '87 GN out of storage yesterday and after checking all fluids, took it for a ride.

The motor / trans is completely stock with 90,000 miles.

When giving it WOT, a loud shriek comes from somewhere around the middle of the dashboard but I cannot tell if it is in or outside the car. It's not as easy to invoke the noise when revving the car underhood at the throttle body. Seems I have to free rev it dangerously high to get the noise, and then it's noisy for only a split second. When driving, on the other hand, just kicking it down from 20 mph and holding it to the floor makes it shriek like a banshee.

It doesn't seem to be down on power but the shriek is so disconcerting, I just let off right away so I can't say for certain she's pushing all the ponies she usually does.

My friend who is a mechanic but unfortunately only had time to take a ride to hear it, thought it was an "air" noise and not a friction or mechanical noise. He suggested that I focus my attention on vacuum or boost plumbing. I plan to do that but thought if this was a more common issue issue with the TB's then it might save me some time looking for the needle in the haystack.

I'm stumped so any suggestions will be much appreciated!

Chris

 

[Squid4life]

I would look closely at the turbo. Pull the inlet hose and downpipe off and check the wheels. Oftentimes the sound at high RPM is the wheels of the turbo making contact within the housing.

 

[Rdirks]

If it only happens under boost.....

Could be an air leak. Mine had a similar issue last year that drove me nuts. Otto's Performance helped me figure out that the EGR was leaking under boost. Easy fix once you find the problem. (Thanks Otto)

Rich

 

[Dash65]

Thanks for the quick replies fellas!
Yeah it does "seem" to only occur under boost (or very high revs). I will take a look around the EGR and the turbo itself to see if something is cracked or actually hitting the housing.

Maybe I'll take a look at the line that feeds the boost gauge if I can dig up that vacuum line diagram from an older post.

My buddy thought it was an air leak from the noise but my hearing is shot so I can't trust what I hear...and only about half of what I see!

If anyone has any other suggestions for me to follow, just keep 'em coming.

 

[notacarlo]

If anyone has any other suggestions for me to follow, just keep 'em coming.

Stop no load revving that motor.

Can you record this sound?
When you say high rpm, what exactly is the rpm range?
Do you have a cold air kit (open air filter) ?
Are the boots from the turbo to the intercooler to the tb tight?

 

[lgonzalez_1986]

if you rev it at park will it stil make the same noise or only when your driving? if not air leak look into a dried out u joint you said it was is storage. my mustang did the same thing at high speeds but turned to be a worn u joint

 

[drturbo69]

Had a crossover pipe that would do that only after hot-after boosting several times crossover pipe was glowing red.
Doc

 

[lgonzalez_1986]

glowing red, huh> wicked! need one of those on my car!

 

[Dash65]

Thanks again for the suggestions guys!
notacarlo - you're right, no load revving is a terrible thing to do to a motor but I needed to try it to determine if the noise was related to the car going down the road vs just high revs.
I'll try to get a recording...not sure if my iPod (gratuitous plug for Apple:wink can pick it up on the voice recorder.
No cold-air kit
About 4k rpm...untrustworthy tach so that's a bit of a guess.
I will check all of the turbo to intercooler and silicone fittings closely to see if one of those has failed. On first look they were ok but I ran out of time/daylight for a more thorough look.
I'm hesitant to give 'er the spurs when it isn't up to operating temperature to test out if the noise happens at all temps. Do you guys concur I should hold off doing that test?

 

[Dash65]

Squeal at High Revs Solved!

Hey guys,
Found the culprit...it was the flexible tube between the MAF sensor housing and the turbo. It had a 2 inch slit right before the turbo just out of sight making it harder to locate. Fortunately I had a brand new one just waiting for installation so that worked out well. Car is running stronger now which makes sense now that its not gulping air that the MAF sensor had no idea about.
Thanks again everyone and have a great weekend!
Chris