another vacuum leak...

2000 oldsmobile bravada

after recent engine replacement, i've noticed a vacuum leak that appears to be under my dash. (i can't take it back to the same mechanic-long story) my auto climate control all works fine, my brakes work fine-everything works fine, but this hissing sound is driving me crazy! all vacuum lines running thru the firewall are ok. the hissing changes upon pressing the accelerator and letting up, and when i turn off the engine, it hisses for about 3 seconds afterwards.

i posted in march, but since then i have checked further. all vacuum leaks that i have researched here seem to be related to manual climate control functions, but my auto controls all work fine. any ideas?

2000 oldsmobile bravada

after recent engine replacement, i've noticed a vacuum leak that appears to be under my dash. (i can't take it back to the same mechanic-long story) my auto climate control all works fine, my brakes work fine-everything works fine, but this hissing sound is driving me crazy! all vacuum lines running thru the firewall are ok. the hissing changes upon pressing the accelerator and letting up, and when i turn off the engine, it hisses for about 3 seconds afterwards.

i posted in march, but since then i have checked further. all vacuum leaks that i have researched here seem to be related to manual climate control functions, but my auto controls all work fine. any ideas?

You need to look under there and have a look and listen for where it is coming from.

Does noise change when the brake pedal is pressed down?

no, the brakes work perfectly. there is a constant "shhhh" sound, and another "pshhhht" sound that changes with accelerator pedal movement.

it was suggested to me that the source of the vacuum leak would be behind the climate control. but before i pulled the dash apart, i wondered why the climate control functions would work perfectly if it was related to the controls. i've read other posts about the same sounding vacuum leak being related to manual climate controls, and airflow direction being affected.

so i've been told it is a vacuum leak for sure, but the tech would have to tear into the dash to find the source. and because the tech isn't sure, i would have to pay an uncertain labor amount until he found it. i had hoped to find it myself before paying him to find it.

no, the brakes work perfectly. there is a constant "shhhh" sound, and another "pshhhht" sound that changes with accelerator pedal movement.

it was suggested to me that the source of the vacuum leak would be behind the climate control. but before i pulled the dash apart, i wondered why the climate control functions would work perfectly if it was related to the controls. i've read other posts about the same sounding vacuum leak being related to manual climate controls, and airflow direction being affected.

so i've been told it is a vacuum leak for sure, but the tech would have to tear into the dash to find the source. and because the tech isn't sure, i would have to pay an uncertain labor amount until he found it. i had hoped to find it myself before paying him to find it.


Before pulling dash have a look and listen under there and see if you can find where the leak is.
If engine was replaced I would check under hood first.
Sound can travel.

If no vacuum leaks under hood poke your head and ear under dash.
Is leak from center of dash or around steering wheel and or rear of brake booster.
If center of dash around heater/ac housing.
Pull heater controls panel and check vacuum line on back of it and then block vacuum going to it and see if leak quits.

Post back what you find there.

ok...so i did some further checking as requested. i started to pull apart the dash, then decided to lift the hood and listen/check under there. i have isolated the source of the "vacuum leak", or annoying "shhhhhh" noise. but, i don't know what the part is. it is located on top of the engine, behind the throttle body, but in front of the ignition coil. it has many small colored wires coming out of it on the passenger side. i could feel it "engaging" and hear it making noise while turning the ignition forward and back. i pulled the rectangular suspect part and noticed there is an orange gasket around it that was torn. i tired finding out what the part is at the gm dealer. they showed me a gasket kit that did seem to contain the orange gasket that would fit in this part, and hopefully silence the noise. this part seems related to the fuel system. i'm going to check the junk yard for this gasket. usually, they just give me these small type parts free anyway. what is this thing?

Don't waste your time with a used one, get a new one. That gasket fits onto the fuel injector housing and seals the gap to the upper intake manifold. The wires go the each individual fuel injector. The upper intake manifold must be removed to replace the seal. Tell the parts store you need the "upper intake manifold gasket set". When you have the intake off, replace all of the gaskets that come in the kit.