90Gt squeal/chirp when hot

[Bvoss59]

Hi, I am new to the forum but I’m hoping the community will be able to help me out.

I have a 90 Gt with the stock 302. No major mods just cold air intake, cobra upper and lower intakes. BBK headers, catless h-pipe and a smog pump delete(only took it off because the pump seized and I didn’t want to replace it) Nothing else major.

My issue is I have a squeal that I can’t track down that is driving me crazy. It sounds like an accessory bearing going out but it is located on the passenger side near the throttle body but lower in the engine. The car does not squeal until the engine gets hot. I have taken off the accessory belt and it still squeals/chirps. It is louder under the car near the transmission and twice as loud on the passenger side compared to the driver side. I thought it might be the throw out bearing but pushing in the clutch makes little to no difference. Also when the car idles down below 800rpm the squeal will go away. When I shut the car off it continues for a second and the pitch increases almost like a vacuum leak. I have sprayed brake clean to see if the rpm increase to look for a vacuum leak but it does not increase (I’ll try it again when I get more cleaner) I have leaky valve cover gaskets that I’m going to replace this weekend but didn’t think that would make the sound.

At this point I’m lost seems like a bad bearing because of the chirping noise but also sounds like a vacuum leak any help is appreciated.

I have a video on YouTube not sure if I can post a link

 

[AeroCoupe]

So when you say this:

“When I shut the car off it continues for a second and the pitch increases almost like a vacuum leak.”

Are you saying the engine is stopped? If so it’s nothing in the rotating assembly.

 

[General karthief]

Post the link.
I was thinking pilot bearing until you said it continued after shut off.
There are two vacuum cans, one looks like a can the other like a bulb with legs, under the right fender, you have to pull the liner down to get to them, the vac lines that feed them run behind the right shock tower by the hood hinge.
Best I can do from a keyboard. Well, that and spell check...

 

[Bvoss59]

View: https://youtube.com/shorts/kjgDZYuIP8A?si=APCa_p2GtLUlD_7j

 

[Bvoss59]

I’ll try to get a better video tomorrow of the noise and what it does when I shut the engine off. It makes the noise while the engine is winding down about a second after I turn the key to shut the engine off like the vacuum is equalizing pressure but the chirp sounds like a bearing.

 

[Bvoss59]

I’ll have to pull off the fender liner and see if it’s coming from there. I bought a stethoscope to see if I can narrow it down but didn’t help

 

[General karthief]

The noise I hear also sounds like a bearing.

 

[Bvoss59]

Post the link.
I was thinking pilot bearing until you said it continued after shut off.
There are two vacuum cans, one looks like a can the other like a bulb with legs, under the right fender, you have to pull the liner down to get to them, the vac lines that feed them run behind the right shock tower by the hood hinge.
Best I can do from a keyboard. Well, that and spell check...

View: https://youtube.com/shorts/W8bWqMLGWzs?si=rO5RToFMzCJctr8x

 

[Bvoss59]

The noise I hear also sounds like a bearing.

View: https://youtube.com/shorts/FnFHMG6cvz4?si=5bz3Rp_N-CSPAs5z

 

[Bvoss59]

Sorry late response, I think I have determined I have a bad harmonic balancer that is causing some of the noise. It has a bad wobble and got louder when I removed the serpentine belt, and definitely coming from the front of the motor. The noise seemed much louder and I have a new vibration in the motor while driving. It’s the squeal at the end when I shut the car off has me stumped. Sounds like a bad vacuum leak and comes from the top of the motor when the engine is shut off.

 

[AeroCoupe]

IF you know the harmonic balancer needed to be replace then do that and see what it sounds like after that. The more things you can take out of the equation the better. I almost wonder if the outer ring and inner on the harmonic balancer are running at different speeds and when you shut the motor off the noise stops when they both stop. That is really a stretch but until you replace the damn thing its a possibility.

 

[Bvoss59]

I just picked one up from the parts store and I’m replacing it now. I’ll post an update once I’m done and take it for a test drive. Definitely sounds like two different noises.

 

[Bvoss59]

IF you know the harmonic balancer needed to be replace then do that and see what it sounds like after that. The more things you can take out of the equation the better. I almost wonder if the outer ring and inner on the harmonic balancer are running at different speeds and when you shut the motor off the noise stops when they both stop. That is really a stretch but until you replace the damn thing its a possibility.

Just finished replacing the harmonic balancer and still have the squeal. It needed to be replaced anyway it was really wobbly but I’m at a loss.

 

[General karthief]

Get a vacuum gauge, plug it into the vacuum tree, watch the gauge, is it steady or wobble or pulse?
as the engine is turned off, w watch the gauge, does it drop slowly with the sound or does it drop to zero like a switch.
have you removed all the air pump hoses?

 

[Bvoss59]

I will check the vacuum lines next and pull them one by one till the noise hopefully goes away. The interesting thing is the noise does not start till the engine gets hot. Could it be an intake or valve cover gasket leak. Seems as the engine heats up and the metal expands it opens up the leak. If I crack the oil fill open the noise goes away but also the engine idles down and when it is below 800 rpm the noise goes away. How much vacuum should be pulled in through the valve covers. I have new valve cover and upper intake gaskets I’m going to install sometime this week

 

[Bvoss59]

Get a vacuum gauge, plug it into the vacuum tree, watch the gauge, is it steady or wobble or pulse?
as the engine is turned off, w watch the gauge, does it drop slowly with the sound or does it drop to zero like a switch.
have you removed all the air pump hoses?

The smog pump seized so I removed all of the hoses and capped off the pipe coming from the heads.

 

[General karthief]

If I crack the oil fill open the noise goes away but also the engine idles down and when it is below 800 rpm the noise goes away.

this would have been good to know earlier or did you just discover this?
Have you looked at the PCV and hoses?

 

[Bvoss59]

this would have been good to know earlier or did you just discover this?
Have you looked at the PCV and hoses?

Found it out recently. I replaced the pcv valve grommet and the oil separator thing below the grommet. Got the whole kit from LMR. Turns out it had fallen out and was just hanging by the hose. the previous owner used rtv to hold the grommet in place and it didn’t hold, hopefully didn’t do any damage missing the pcv for a while.

 

[AeroCoupe]

At this point I am going to say you have excessive blow by. Check al the vacuum lines and if you do not find anything then you need to to a leak down test.

 

[Bvoss59]

At this point I am going to say you have excessive blow by. Check al the vacuum lines and if you do not find anything then you need to to a leak down test.

Would excessive blow by decrease the vacuum pressure. When I pull the oil cap while the engine is running it’s pulls a large amount of vacuum and suck air into the engine. And when I shut the engine off I hear the engine sucking in air to equalize pressure. When the vacuum pressure drops the squeal stops. I’ll try a leak down test after I try replacing the intake and valve cover gaskets and checking all the vacuum lines.