Help finding vacuum leak
01-01-2019, 07:46 PM
#1
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Car: 1990 IROC-Z
Engine: 5.0 TBI
Transmission: 700R4
Help finding vacuum leak
Hi all, been lurking here for about 6 months as I searched for my own 3rd gen. Well I finally got one, a 1990 IROC-Z 5.0 TBI with some suspension mods already done. First 3rd gen but not first Camaro and I know my way around a vehicle/garage. Now I need to enlist the help of the wiser, more experienced folks.
I know I have a vacuum leak somewhere. Here is what I can tell: The engine is idling/running very fast and rich. There is a loud high pitch hiss coming from (I think) passenger side. The HVAC will not switch from the defrost setting and I have checked the typical issue at the control head and that is still in good shape. The vacuum line going from the HCV to the control head is missing entirely.
Thus far I have done a tuneup, visually inspected what lines I can see and found only stiff lines and old gaskets in the TBI, and pulled the HVAC control head to check the switch. I have also sprayed a few shots of starter fluid under the hood to see if I could find the leak but no results.
If if any one has diagrams for the HVAC vacuum lines or pictures that could help show me where to look or any suggestions I would be greatful. So far a search has not been helpful. Thanks.
Slice
I know I have a vacuum leak somewhere. Here is what I can tell: The engine is idling/running very fast and rich. There is a loud high pitch hiss coming from (I think) passenger side. The HVAC will not switch from the defrost setting and I have checked the typical issue at the control head and that is still in good shape. The vacuum line going from the HCV to the control head is missing entirely.
Thus far I have done a tuneup, visually inspected what lines I can see and found only stiff lines and old gaskets in the TBI, and pulled the HVAC control head to check the switch. I have also sprayed a few shots of starter fluid under the hood to see if I could find the leak but no results.
If if any one has diagrams for the HVAC vacuum lines or pictures that could help show me where to look or any suggestions I would be greatful. So far a search has not been helpful. Thanks.
Slice
01-01-2019, 08:07 PM
#2
Re: Help finding vacuum leak
This doesn’t show hvac but it comes from manifold vacuum to the hardline in the passengers side wiring loom.
It does have a line running from the inside switch to the heater control valve.the base gasket of the tbi is the most common vacuum leak source.
01-02-2019, 09:00 PM
#3
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Re: Help finding vacuum leak
Whenever I come to a car that I have no idea how things are routed (every car except like 3 in the world)
I always do the same test: Pressure test.
Block the PCV system so it doesn't pressurize the crankcase, then apply "boost pressure" to the intake manifold and find all the leaks in every conceivable... um ... place.
It will sound like air leaking 'Hissssss'
I have a video somewhere.... crappy camera basic test...
Here we go
I always do the same test: Pressure test.
Block the PCV system so it doesn't pressurize the crankcase, then apply "boost pressure" to the intake manifold and find all the leaks in every conceivable... um ... place.
It will sound like air leaking 'Hissssss'
I have a video somewhere.... crappy camera basic test...
Here we go
01-04-2019, 08:16 PM
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Car: 1992 1le z03 1992 b4c camaros
Engine: 305 tpi 350 auto
Re: Help finding vacuum leak
Spraying carburetor cleaner around intake should find an external vacuum leak.Also a stuck EGR valve will cause a bad vacuum leak that cannot be checked with carb cleaner because it's an internal vacuum leak.Try tapping on the EGR valve with the car running and listen for a change in rpm.A vacuum gauge would be helpful.A steady 15 inch vacuum reading would be a good normal reading
01-06-2019, 07:36 PM
#5
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Re: Help finding vacuum leak
I dont fully trust carb cleaner or smoke tests because some leaks dont show up until there is a pressure difference (vacuum or boost)
01-07-2019, 10:26 PM
#6
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Car: 1990 IROC-Z
Engine: 5.0 TBI
Transmission: 700R4
Re: Help finding vacuum leak
I’ve tried the starter fluid and didn’t hear any change. Granted I was being real cautious since I don’t want a fire inadvertently. I will try using the compressed air like you suggested. Tapping on the EGR resulted in no changes so I don’t think that’s it. It’s a really loud audible whistle.
01-08-2019, 12:07 PM
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Car: 1989 Firebird
Engine: 5.7 LS1
Transmission: T56
Re: Help finding vacuum leak
Don't forget the vacuum "ball" and cruise control under the driver front corner, as well as the vacuum line that runs from it to the brake pedal.
There is a single supply vacuum source to the AC. I would cap that off and see if it improves, if it does you know its within the maze of vacuum lines driving your vents and heater control valve.
EGR/PCV/etc.
The check valve in the the brake booster and or the brake booster.
Not quite as bad as a 90's Honda but a lot of spots it could be-- the car is old enough it wouldn't be a waste of money to just replace all vacuum lines you can see.
There is a single supply vacuum source to the AC. I would cap that off and see if it improves, if it does you know its within the maze of vacuum lines driving your vents and heater control valve.
EGR/PCV/etc.
The check valve in the the brake booster and or the brake booster.
Not quite as bad as a 90's Honda but a lot of spots it could be-- the car is old enough it wouldn't be a waste of money to just replace all vacuum lines you can see.
Last edited by Aviator857; 01-08-2019 at 12:32 PM.
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01-08-2019, 09:05 PM
#8
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Car: 1990 IROC-Z
Engine: 5.0 TBI
Transmission: 700R4
Re: Help finding vacuum leak
Don't forget the vacuum "ball" and cruise control under the driver front corner, as well as the vacuum line that runs from it to the brake pedal.
There is a single supply vacuum source to the AC. I would cap that off and see if it improves, if it does you know its within the maze of vacuum lines driving your vents and heater control valve.
EGR/PCV/etc.
The check valve in the the brake booster and or the brake booster.
Not quite as bad as a 90's Honda but a lot of spots it could be-- the car is old enough it wouldn't be a waste of money to just replace all vacuum lines you can see.
There is a single supply vacuum source to the AC. I would cap that off and see if it improves, if it does you know its within the maze of vacuum lines driving your vents and heater control valve.
EGR/PCV/etc.
The check valve in the the brake booster and or the brake booster.
Not quite as bad as a 90's Honda but a lot of spots it could be-- the car is old enough it wouldn't be a waste of money to just replace all vacuum lines you can see.
i just found a bad line by the cruise control as that was not something I had looked at yet. Do you happen to have a picture or diagram of the AC vacuum line location? I know there is something up with the HVAC but don’t know where to start.
Agree that systematically replacing the lines is the right way to go I just wish I could find full diagrams of them. Service manual perhaps? So far I’ve only found the one above.
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