Vac leaks...best way to test?
- Thread starter savage6
- Start date
MistaScott
Abnormally Aspirated
- Joined
- Oct 18, 2003
Buy a MityVac at Autozone/Sears for $25. It is a vacuum pump that allows you to measure and hold vacuum in a line. It also can be used as a brake bleeder kit.
This is the real deal way to find leaks. Spraying carb cleaner on the lines and visual inspection isn't nearly as effective.
This is the real deal way to find leaks. Spraying carb cleaner on the lines and visual inspection isn't nearly as effective.
MistaScott is right, I finally broke down and bought a Mighty-Vac, and it makes chasing vacuum leaks a lot easier. Then go to NAPA or where ever and buy a couple of feet of the various sizes of vacuum line and start replace everything, that way you make sure all the lines are good and you get to learn more the fun things about your engine 
. I even zip-tie them to be double sure after replacing (i've even considered getting some "liquid electrical tape" to dip the ends in but haven't yet). After you have eliminated vacuum line leaks it makes detecting "real" leaks easier, don't forget to test the check valves as well. It is usually the little stuff that gives problems, a little leak here, a weak check-valve there, they add up real quick! My G/N is very sensitive to vac. leaks. Another area is the plenum/intake, if you have removed to install a power plate etc. you must assure the gasket is sealed and the bolts snug (be careful about stripping the threads or you will get a major vac leak been there, done that ).
ANyway, the Mighty-Vac is worth the $$
D.
. I even zip-tie them to be double sure after replacing (i've even considered getting some "liquid electrical tape" to dip the ends in but haven't yet). After you have eliminated vacuum line leaks it makes detecting "real" leaks easier, don't forget to test the check valves as well. It is usually the little stuff that gives problems, a little leak here, a weak check-valve there, they add up real quick! My G/N is very sensitive to vac. leaks. Another area is the plenum/intake, if you have removed to install a power plate etc. you must assure the gasket is sealed and the bolts snug (be careful about stripping the threads or you will get a major vac leak been there, done that ).ANyway, the Mighty-Vac is worth the $$
D.
- Joined
- Jul 20, 2001
If you have a scan tool, use it to find your vacuum leaks. Just spray the suspected area (with carb cleaner or propane) of the vacuum leak and watch your O2 sensor readings. As soon as you encounter a leak, the O2 readings will shoot up.
0-60 in 3.6
New Member
- Joined
- Jun 9, 2001
Vacuum Leak
Savage6,
Here are a few tips from the archives. Credit goes to other TurboBuick.com members, not me.
Read the following, search the archives some more (for "High BLM" as well as "vacuum leak.") Most of all, be patient. You'll find your leaks.
HTH
Peter
87GN
-----------------------------
When I am looking for vacuum leaks, I use carb spray (WD-40 is a lube and leaves an oily deposit... This attracts dust.) Target areas are the gaskets at the vacuum block, dog house, plenum, intake, PCV grommet, EGR lines (At the valve and solenoid), and the vacuum canister itself.
-------------------------------
That solenoid on top of the cannister should hold vacuum if its applied to its nipple, if it doesnt its bad. If that solenoid is bad, the check valve going to it was probably bad as well. Evertime you find something bad your one step closer. Sorry the car is close to 20 years old. Stuff happens.
Plug all the lines on top of the throttle body. Easy way to do this, remove the two screws on top of the vacuum block, lift it a little, and put something there to seal it. I use gasket material(plain) they sell it in a roll, with some dressing(hylomar, vaseline), push the two screws through it, and tighten them down. This way there is no vacuum going to any accessory. Doing so should drop your BL's down under 120 typically, if theyre still at 150..your issue is elsewhere.
-------------------------------
I'll give you this tip.. put a piece of blank gasket material over the TB under the vacuum distribution block. your BLM's should go under 128 to about 120. If so..then you have one of the lines with issues. If not.. look else where for your leak.. like headers, plenum gaskets, IAC gaskets, MAF, O2 sensor, etc
If the check valve under the FPR was toast, the EGR selenoid valve may be bad. Remove the sponge filter, apply vacuum with the mity vac, it should hold vacuum when you put your finger over the nipple. If it makes a farting sound, its probably bad.
Understand what bl 150 means. The O2 sensor reads that the mixture is lean, and is commanding the ecm to add fuel. Lean happens from too much air. Where is the too much air.. this is where your at. You have to isolate the motor.. air leak anywhere can do this. Bad MAF, bad O2, cracked header, throttle body, FPR, TB gasket, plenum gasket, intake gasket, cam, vacuum block gasket, bad injector, IC, Turbo, chip, ecm, ignition module, etc etc etc... If I sound repetitive.. sorry. see if even didnt mention vacuum lines.
Everytime you find a vacuum breach.. reset the computer and try again. Do the top engine cleaner to check for exhuast leaks, place the MAF rite before the throttle body eliminating the turbo and IC... what can I say..you dont fix this, you'll hurt your motor driving it this way. Why becuase the extra fuel it's dropping in will wash down the cylinders and mess the oil up. Bad oil, can hurt the bearings, wash down can hurt the rings/walls. Let alone your fuel tables now are skewed up.. the idle BL's set up the basis for your computers tuning.. cant tell you how many blown head gaskets i've seen with cars that have a high bl problem.
Do some searching, or get the car to someone that can diagnose this kind of issue. Its usually something simple..problem is its hard to find. I hate this kind of stuff.. much easier to do headgaskets than constantly prod around a motor hoping to find the issue.
-----------------------------------
If you look under your FPR there is a metal line, from it goes to a one way check valve. From it there is a "T" fitting. One part of the T goes to the EGR, the other to your vacuum accessories. Right behind the brake booster along the firewall there is a vacuum hose that runs to the cruise control and vacuum ball. if you unhook the rubber from wher it branches, this is the place to test it. It will take quite a few pumps for the needle to start going up if everything is ok. Since you have to evac the air out of the ball. Anyways that hose rots on almost all the cars I've ever looked at.
There is another line that goes through another check valve to your cannister. Its the nipple behind the alternator. If you pull that hose, it should hold vacuum as well. If it doesnt, then its a bad check valve/hose/cannister valve. This being done car off.
The EGR solenoid is bit tricky to test. See you have to remove the cover on the back, remove the little filter, apply vacuum to the larger nipple on the front, and while holding your finger to plug the air filter nipple hole, it should hold vacuum. At least some.. a couple inches is all thats needed without the needle on the guage falling.
The check valves go bad due to age and what not.. once they go bad, they allow boost to go past them.. once this happens, it kills the diaphrams in those units.. not always.. but happens.
Lastly on your brake booster there is a check valve that lets it hold pressure. Its that black plastic thing on the end of the hose rite where it plugs into the booster. No that has no bearing on your blm problem unless the booster doesnt hold vacuum.. If you pull that off the booster you should hear a PSSSHHHH.
--------------------------------------
Well I have officially fixed three cars with the high BLM condition...
Mity Vac is your best friend when it comes to this.
First car, ended up needing two check valves(GM), EGR selenoid, Charcoal cannister selenoid, AC Delco PCV, and 4 vacuum lines replaced.
Second car was easy.. two check valves, one EGR selenoid, one charcoal cannister selenoid, two vacuum lines..and an AC Delco PCV.
Third was the monster.. stripped bolts on intake repaired, leaky EGR valve replaced, 6 vacuum hoses, 2 check valves, AC Delco PCV, installed new power plate gaskets, cracked drivers side header welded, installed missing TB gasket , and replaced the already new vacuum block gasket.. BLM's are 128 at idle. This car was at 160 at idle.. oil was being changed every 300 miles cuase it smelled like fuel. Wont mention gas economy.
Famous quote from mechanic.. "I dunno..car seems to be running really good(BLM at 148)..you sure your just not chasing numbers?"
What happens is the check valves go bad and let boost through..then when this happens, its blows out the diaphrams on the associated stuff like EGR selenoids and charcoal cannister selenoids. One of the cars had those cheap discount autoparts check valves..new.. they were bad. Replace all the crap with original AC Delco and you'll be amazed at the results. Pinching pennies on this stuff comes back in a vicious way.
FWIW, on the easy car that was at 146.. replacing the PCV to an AC Delco PCV dropped that car from 146 to 137.
Hope this helps someone searching. Two of the cars above had sustained blown head gaskets.. wonder why?
Savage6,
Here are a few tips from the archives. Credit goes to other TurboBuick.com members, not me.
Read the following, search the archives some more (for "High BLM" as well as "vacuum leak.") Most of all, be patient. You'll find your leaks.
HTH
Peter
87GN
-----------------------------
When I am looking for vacuum leaks, I use carb spray (WD-40 is a lube and leaves an oily deposit... This attracts dust.) Target areas are the gaskets at the vacuum block, dog house, plenum, intake, PCV grommet, EGR lines (At the valve and solenoid), and the vacuum canister itself.
-------------------------------
That solenoid on top of the cannister should hold vacuum if its applied to its nipple, if it doesnt its bad. If that solenoid is bad, the check valve going to it was probably bad as well. Evertime you find something bad your one step closer. Sorry the car is close to 20 years old. Stuff happens.
Plug all the lines on top of the throttle body. Easy way to do this, remove the two screws on top of the vacuum block, lift it a little, and put something there to seal it. I use gasket material(plain) they sell it in a roll, with some dressing(hylomar, vaseline), push the two screws through it, and tighten them down. This way there is no vacuum going to any accessory. Doing so should drop your BL's down under 120 typically, if theyre still at 150..your issue is elsewhere.
-------------------------------
I'll give you this tip.. put a piece of blank gasket material over the TB under the vacuum distribution block. your BLM's should go under 128 to about 120. If so..then you have one of the lines with issues. If not.. look else where for your leak.. like headers, plenum gaskets, IAC gaskets, MAF, O2 sensor, etc
If the check valve under the FPR was toast, the EGR selenoid valve may be bad. Remove the sponge filter, apply vacuum with the mity vac, it should hold vacuum when you put your finger over the nipple. If it makes a farting sound, its probably bad.
Understand what bl 150 means. The O2 sensor reads that the mixture is lean, and is commanding the ecm to add fuel. Lean happens from too much air. Where is the too much air.. this is where your at. You have to isolate the motor.. air leak anywhere can do this. Bad MAF, bad O2, cracked header, throttle body, FPR, TB gasket, plenum gasket, intake gasket, cam, vacuum block gasket, bad injector, IC, Turbo, chip, ecm, ignition module, etc etc etc... If I sound repetitive.. sorry. see if even didnt mention vacuum lines.
Everytime you find a vacuum breach.. reset the computer and try again. Do the top engine cleaner to check for exhuast leaks, place the MAF rite before the throttle body eliminating the turbo and IC... what can I say..you dont fix this, you'll hurt your motor driving it this way. Why becuase the extra fuel it's dropping in will wash down the cylinders and mess the oil up. Bad oil, can hurt the bearings, wash down can hurt the rings/walls. Let alone your fuel tables now are skewed up.. the idle BL's set up the basis for your computers tuning.. cant tell you how many blown head gaskets i've seen with cars that have a high bl problem.
Do some searching, or get the car to someone that can diagnose this kind of issue. Its usually something simple..problem is its hard to find. I hate this kind of stuff.. much easier to do headgaskets than constantly prod around a motor hoping to find the issue.
-----------------------------------
If you look under your FPR there is a metal line, from it goes to a one way check valve. From it there is a "T" fitting. One part of the T goes to the EGR, the other to your vacuum accessories. Right behind the brake booster along the firewall there is a vacuum hose that runs to the cruise control and vacuum ball. if you unhook the rubber from wher it branches, this is the place to test it. It will take quite a few pumps for the needle to start going up if everything is ok. Since you have to evac the air out of the ball. Anyways that hose rots on almost all the cars I've ever looked at.
There is another line that goes through another check valve to your cannister. Its the nipple behind the alternator. If you pull that hose, it should hold vacuum as well. If it doesnt, then its a bad check valve/hose/cannister valve. This being done car off.
The EGR solenoid is bit tricky to test. See you have to remove the cover on the back, remove the little filter, apply vacuum to the larger nipple on the front, and while holding your finger to plug the air filter nipple hole, it should hold vacuum. At least some.. a couple inches is all thats needed without the needle on the guage falling.
The check valves go bad due to age and what not.. once they go bad, they allow boost to go past them.. once this happens, it kills the diaphrams in those units.. not always.. but happens.
Lastly on your brake booster there is a check valve that lets it hold pressure. Its that black plastic thing on the end of the hose rite where it plugs into the booster. No that has no bearing on your blm problem unless the booster doesnt hold vacuum.. If you pull that off the booster you should hear a PSSSHHHH.
--------------------------------------
Well I have officially fixed three cars with the high BLM condition...
Mity Vac is your best friend when it comes to this.
First car, ended up needing two check valves(GM), EGR selenoid, Charcoal cannister selenoid, AC Delco PCV, and 4 vacuum lines replaced.
Second car was easy.. two check valves, one EGR selenoid, one charcoal cannister selenoid, two vacuum lines..and an AC Delco PCV.
Third was the monster.. stripped bolts on intake repaired, leaky EGR valve replaced, 6 vacuum hoses, 2 check valves, AC Delco PCV, installed new power plate gaskets, cracked drivers side header welded, installed missing TB gasket , and replaced the already new vacuum block gasket.. BLM's are 128 at idle. This car was at 160 at idle.. oil was being changed every 300 miles cuase it smelled like fuel. Wont mention gas economy.
Famous quote from mechanic.. "I dunno..car seems to be running really good(BLM at 148)..you sure your just not chasing numbers?"
What happens is the check valves go bad and let boost through..then when this happens, its blows out the diaphrams on the associated stuff like EGR selenoids and charcoal cannister selenoids. One of the cars had those cheap discount autoparts check valves..new.. they were bad. Replace all the crap with original AC Delco and you'll be amazed at the results. Pinching pennies on this stuff comes back in a vicious way.
FWIW, on the easy car that was at 146.. replacing the PCV to an AC Delco PCV dropped that car from 146 to 137.
Hope this helps someone searching. Two of the cars above had sustained blown head gaskets.. wonder why?
REGALTURBO
I Am The Master..Master..
- Joined
- Apr 20, 2003
I was wondering what will be the result of a vacume leak. I often wonder if my car has one because at idle it smells very rich and sometimes blows blue smoke. I just installed a wide band O2 monitoring device to look at my A/F ratio at idle. Where should that be? I`m tired of chasing my O2 readings off my scanmaster. The mighty-vac sounds like a good investment to me. I`m going to get one.
TT/Ameasap
The White Blur
- Joined
- Jan 31, 2002
FYI, I just got a bl of 150 in park @ idle and pulled hair out to find it. swapped lots of parts and checked for vacuum leaks..... Finally found it....MAF..... It was working just fine (255 WOT) and everything seemed normal untill I read these post's about bl150.
Swapped in original MAF and BANGO!! BL 124
Change your oil if you have this problem for the sake of your bearings..... Mine smells like gass so I changed it. All is well now.
Thought I would share.
Bo
Swapped in original MAF and BANGO!! BL 124
Change your oil if you have this problem for the sake of your bearings..... Mine smells like gass so I changed it. All is well now.
Thought I would share.
Bo
