Vacuum Leak Sound from Upper Manifold?

savegoodautonfg · May 25, 2006

I removed my upper manifold last week to paint it. I got it off no problem.I put it back on and for some reason it was making a vacuum leak hissing noise. then i took if off again checked all the hoses and evrything was fine. i brought it to my mechanic last night he and his friend took 3 hours trying to figure it out. they called me and said it was done. i picked it up went home and it was still tehre. they looked at eveerything and can not find out what is wrong with it any ideas?

savegoodautonfg · May 25, 2006

also to add... pcv valve was replaced and everytime intake manifold came off new gasket was installed.

Daggar · May 25, 2006

Does it make the sound at idle or just during acceleration?

savegoodautonfg · May 25, 2006

just at idle. it goes away when u hit the gas.

90lxboost'n · May 25, 2006

What's up guys, I have a 90 lx with a trick flow u/l I just installed a few weeks ago and it has a real high pitch whistle sounding vac. leak only at idle also. I searched for it a hundred times and had about 20 friends try to find it but no one can find it. I even sprayed carb cleaner hoping the idle would jump when i found it but no such luck. The leak does not affect how my car runs or that I can tell, but the leaks sounds like I have a blower on the car.

Daggar · May 25, 2006

savegoodautonfg said:
just at idle. it goes away when u hit the gas.

Try loosening the screws for your TPS and rotating it forward/backward in the slots to see if it goes away. My initial thought is that the butterfly valve is just in that perfect position at idle to cause the noise you're describing. You should not need to elongate the holes on the sensor. There's a tiny bit of play in there that may be all that you'll need.

If that works for ya, then just hold the TPS in the position where it stops making the noise then snug up the retaining screws.

Let us know if it work for ya. If not, it's back to the drawing boards. hehe

Also: Try cleaning up the throttle body blade a tad to see if that makes any difference... It probably won't but it was just a thought.

savegoodautonfg · May 26, 2006

thanks for your help ill try that out..

Any other ideas?

HISSIN50 · May 26, 2006

You can remove all the vac hoses to the plenum and intake and plug them, sans one. Make sure the TB butterfly is closed all the way and that all vac fittings are sealed air tight.

Connect a vac gauge to the remaining port. Disable the ignition and fuel systems and crank the motor. If the vac reading is around 4-9", that's decent. A leak of any size will show less than 4".

Good luck.

savegoodautonfg · Jun 2, 2006

What exactly is the throttle body butterfly?

and anyone with any more ideas please post cause i can't figure this damn noise out.

savegoodautonfg · Jun 2, 2006

HISSIN50 said:
You can remove all the vac hoses to the plenum and intake and plug them, sans one. Make sure the TB butterfly is closed all the way and that all vac fittings are sealed air tight.

Connect a vac gauge to the remaining port. Disable the ignition and fuel systems and crank the motor. If the vac reading is around 4-9", that's decent. A leak of any size will show less than 4".

Good luck.

Plugging them all and then starting the engine won't hurt at all. What will it do to the engine if they are'nt plugged in from the hoses they are suppose to be?

HISSIN50 · Jun 3, 2006

savegoodautonfg said:
Plugging them all and then starting the engine won't hurt at all. What will it do to the engine if they are'nt plugged in from the hoses they are suppose to be?

Re-read what I posted - you dont start the engine.

I dont understand your question. If you dont plug all the fittings airtight, you have an invalid test (you seal up all known holes, so any vacuum loss has to be attributed to a bad seal between hard parts).

In general if you have swapped vac lines, it depends. For some it wont matter, but for many (esp on EFI cars, where many of the lines are controlled via solenoids), the car can run like poop if lines are crossed.

Good luck.

HISSIN50 · Jun 3, 2006

savegoodautonfg said:
What exactly is the throttle body butterfly?

It's the throttle-blade inside the throttlebody. When you push the gas pedal, it's what pivots to let in more air.

just4bob50 · Jun 3, 2006

There was a post some time ago on this subject, and I used to have the same problem. It is from the TB. Some one said that they smoothed out the by pass ports in they're IAC with a dremel and the whine or whistle was gone. I tried it on mine when my charger was being repaired and it made a big improvement

savegoodautonfg · Jun 3, 2006

HISSIN50 said:
Re-read what I posted - you dont start the engine.

I dont understand your question. If you dont plug all the fittings airtight, you have an invalid test (you seal up all known holes, so any vacuum loss has to be attributed to a bad seal between hard parts).

In general if you have swapped vac lines, it depends. For some it wont matter, but for many (esp on EFI cars, where many of the lines are controlled via solenoids), the car can run like poop if lines are crossed.

Good luck.

SOo you want me to plug them with plugs or plug them with the hoses that are suppose go on them?

savegoodautonfg · Jun 3, 2006

just4bob50 said:
There was a post some time ago on this subject, and I used to have the same problem. It is from the TB. Some one said that they smoothed out the by pass ports in they're IAC with a dremel and the whine or whistle was gone. I tried it on mine when my charger was being repaired and it made a big improvement

thanks for your input but the sound seems like its coming from right under the upper manifold when u put ur ear by it?

MustangGT92 · Jun 3, 2006

did you check the bottom of the upper intake after you painted it???

HISSIN50 · Jun 3, 2006

savegoodautonfg said:
SOo you want me to plug them with plugs or plug them with the hoses that are suppose go on them?

If one thinks there is a leak between the upper and lower, the point of this is to seal the upper off. With the throttle and every opening (vac line ports) sealed, and the engine being on the other side creating vacuum (via pumping while cranking), if it's sealed up, the vac gauge you attach will read a vacuum.

If there is a leak between gaskets, it wont read a vacuum because there is a leak. You are basically removing all the vac lines which are normally attached, as a source of the leak (since they are disconnected and the ports on the intake are sealed).

This is something that's done when one cant find the source of a vac leak anywhere else but it's known that there is a vac leak.

Good luck.

savegoodautonfg · Jun 4, 2006

HISSIN50 said:
If one thinks there is a leak between the upper and lower, the point of this is to seal the upper off. With the throttle and every opening (vac line ports) sealed, and the engine being on the other side creating vacuum (via pumping while cranking), if it's sealed up, the vac gauge you attach will read a vacuum.

If there is a leak between gaskets, it wont read a vacuum because there is a leak. You are basically removing all the vac lines which are normally attached, as a source of the leak (since they are disconnected and the ports on the intake are sealed).

This is something that's done when one cant find the source of a vac leak anywhere else but it's known that there is a vac leak.

Good luck.

SO disconnect the vac lines from the upper one at a time and start the engine and see if the noise goes away?

HISSIN50 · Jun 4, 2006

savegoodautonfg said:
SO disconnect the vac lines from the upper one at a time and start the engine and see if the noise goes away?

You need to cap off every single vac port at once. Sorry that I dont seem to be able to explain this.

The idea: you are trying to seal the intake completely. Now after sealing all the ports, remove one plug on the intake so you can attach your vacuum gauge. Now your intake is totally sealed up again. When you crank the engine over (you disabled the ignition/fuel system so it wont start), the engine creates vacuum. With no leak, you will get a reading (around 3-7" hg). If you dont see that reading, there is a leak of sorts. You know it's not any vacuum lines or fittings because you just capped/sealed them all off. That leaves mating surfaces as the source of the leak.

It's a PITA test but when everything else is ruled out...................

Good luck.

savegoodautonfg · Jun 4, 2006

HISSIN50 said:
You need to cap off every single vac port at once. Sorry that I dont seem to be able to explain this.

The idea: you are trying to seal the intake completely. Now after sealing all the ports, remove one plug on the intake so you can attach your vacuum gauge. Now your intake is totally sealed up again. When you crank the engine over (you disabled the ignition/fuel system so it wont start), the engine creates vacuum. With no leak, you will get a reading (around 3-7" hg). If you dont see that reading, there is a leak of sorts. You know it's not any vacuum lines or fittings because you just capped/sealed them all off. That leaves mating surfaces as the source of the leak.

It's a PITA test but when everything else is ruled out...................

Good luck.

The hoses i could just disconnected, i dont have to seal those off right?

and i dont know how to disable fuel and ignition system

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