Massive Vacuum Leak
Race Director
Joined: Dec 2004
Posts: 15,025
Likes: 2
A vacuum leak this big is going to have to be visually located. Squirting liquid around on things is not going to temporarily seal the leak. It's too big. I know it is hard, because you have all of the sucking noise coming from the carb.
Le Mans Master
Joined: Aug 2001
Posts: 7,804
Likes: 4
From: Standing still with all my might Texas
Cruise-In X Veteran
St. Jude Donor '09-'11
If it's an automatic take a close look at the line from the manifold to the vacuum modulator.
Actually I would suggest disconnecting and plugging EVERY vacuum line going to the carb and manifold.
If it runs OK get the timing and idle set first, then re-connect each vacuum line one at a time til you find the offending system.
If you still have a vacuum leak with everything disconnected and plugged start spraying carb cleaner all around the carb, manifold, all the gaskets, the EGR valve, and the fittings in the manifold.
When you had the EGR valve off of it did you check to see that it operated properly? There should be holes in the back side of the diaphram can that will allow you to move the diaphram back and forth. Even though it looked clean it could be stuck in the open position.
See if you can get a block off plate for the EGR and install it temporarily to see if it solve your leak. If you can't find a plate use the EGR gasket as a template to cut a temporary plate out of an aluminum can and install it between the EGR and the manifold.
Actually I would suggest disconnecting and plugging EVERY vacuum line going to the carb and manifold.
If it runs OK get the timing and idle set first, then re-connect each vacuum line one at a time til you find the offending system.
If you still have a vacuum leak with everything disconnected and plugged start spraying carb cleaner all around the carb, manifold, all the gaskets, the EGR valve, and the fittings in the manifold.
When you had the EGR valve off of it did you check to see that it operated properly? There should be holes in the back side of the diaphram can that will allow you to move the diaphram back and forth. Even though it looked clean it could be stuck in the open position.
See if you can get a block off plate for the EGR and install it temporarily to see if it solve your leak. If you can't find a plate use the EGR gasket as a template to cut a temporary plate out of an aluminum can and install it between the EGR and the manifold.
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,255
Likes: 82
From: Brampton Ont.
Garys 68
Yes I tried the propane with the rubber hose, it was suggested to me by my neighbour the licence mechanic ( he tried for over an hour to locate the leak with no luck ) with the headlight and booster capped and went through 2 full tanks......no luck.
Yes vacuum advance holds vacuum and works.
nitronick
believe me I know it's hard, I've been trying to find this leak for months. One things that doesn't help is it needs an exhaust due to it being parked for 15 years but I can't even drive it on the road due to the stalling.
Kevin_73
Yes it's an automatic and I had plugged the tranny modulator with no change.
I did plug every line going to the carb and manifold and there was no change. I even sprayed around the intake manifold and no change.
I sprayed carb cleaner around the carb, manifold, EGR. and fitting with no change in rpm.
The mechanic next door had the EGR off and tested it and said it was working ok.
I will try the plate over the EGR when I make one up.
Thanks again for your suggestion and I will keep trying them all.
Frank
Yes I tried the propane with the rubber hose, it was suggested to me by my neighbour the licence mechanic ( he tried for over an hour to locate the leak with no luck ) with the headlight and booster capped and went through 2 full tanks......no luck.
Yes vacuum advance holds vacuum and works.
nitronick
believe me I know it's hard, I've been trying to find this leak for months. One things that doesn't help is it needs an exhaust due to it being parked for 15 years but I can't even drive it on the road due to the stalling.
Kevin_73
Yes it's an automatic and I had plugged the tranny modulator with no change.
I did plug every line going to the carb and manifold and there was no change. I even sprayed around the intake manifold and no change.
I sprayed carb cleaner around the carb, manifold, EGR. and fitting with no change in rpm.
The mechanic next door had the EGR off and tested it and said it was working ok.
I will try the plate over the EGR when I make one up.
Thanks again for your suggestion and I will keep trying them all.
Frank
Drifting
Joined: Nov 2001
Posts: 1,469
Likes: 6
From: 68 427 4.11s Roadster
Why exactly do you think you have a vaccum leak?
What did you do that started this problem or was it there as far as you know before?
Did it idle before and if it did what was changed since then?
Does your timing change when you rev the engine up to 3000-4000? You don't even need to know the value, just that it does change.
Not asking if the springs are on. What is the mechanical timing doing? Is it working, not frozen, and at what rpm?
Idle problem even when hot? I assume so since you said several tanks of gas.
You changed carbs so that shouldn't be the problem.
You did use screws to block the vacuum lines. This may, I say may be a problem. store bought caps, round phillips screw drivers or golf tees. Something smooth and something that eliminates the hoses if possible.
The store bought caps go directly on the fittings and will eliminate all hoses. The intake manifold Tee, maybe the threads are leaking?
Stethascope hose to the intake to head mating area might find a leak.
I'm wondering though that this isn't a vaccum leak.
What is the problem?
It doesn't idle lower than 1100-1200. Anything below this and the engine stalls.
Exhaust is shot. Not sure if this can be the problem or not.
What did you do that started this problem or was it there as far as you know before?
Did it idle before and if it did what was changed since then?
Does your timing change when you rev the engine up to 3000-4000? You don't even need to know the value, just that it does change.
Not asking if the springs are on. What is the mechanical timing doing? Is it working, not frozen, and at what rpm?
Idle problem even when hot? I assume so since you said several tanks of gas.
You changed carbs so that shouldn't be the problem.
You did use screws to block the vacuum lines. This may, I say may be a problem. store bought caps, round phillips screw drivers or golf tees. Something smooth and something that eliminates the hoses if possible.
The store bought caps go directly on the fittings and will eliminate all hoses. The intake manifold Tee, maybe the threads are leaking?
Stethascope hose to the intake to head mating area might find a leak.
I'm wondering though that this isn't a vaccum leak.
What is the problem?
It doesn't idle lower than 1100-1200. Anything below this and the engine stalls.
Exhaust is shot. Not sure if this can be the problem or not.
Drifting
Joined: Nov 2003
Posts: 1,874
Likes: 7
From: l In
Originally Posted by Techno
I had a similar problem but the engine was new. Turned out the weights flew out at such a low RPM that adjusting the idle pulled the weights in, retarded the timing. There was a huge dead spot where the engine wouldn't run. Just like you got.
After it broke in the problem went away but its worth checking if your mechanical timing is all in about this rpm point.
If this is the problem it also means your timing is wrong. Your static timing would probably be retarded.
Rev it up and see if your getting any mechanical timing. If you are then this isn't the problem.
If you aren't then you need more static timing to get it to idle without mechanical timing.
What normally would be static timing is for you total timing. If this is the prob.
After it broke in the problem went away but its worth checking if your mechanical timing is all in about this rpm point.
If this is the problem it also means your timing is wrong. Your static timing would probably be retarded.
Rev it up and see if your getting any mechanical timing. If you are then this isn't the problem.
If you aren't then you need more static timing to get it to idle without mechanical timing.
What normally would be static timing is for you total timing. If this is the prob.
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,255
Likes: 82
From: Brampton Ont.
Techno
Why exactly do you think you have a vaccum leak?
If I put my hand on the primary or slighly close the choke when the car is up to temperature the idle revs as high as 700 rpm more.
What did you do that started this problem or was it there as far as you know before?
The car has been stored for over 15 years and It was my daily driver before then.
Did it idle before and if it did what was changed since then?
Stored 15 years.
Does your timing change when you rev the engine up to 3000-4000? You don't even need to know the value, just that it does change.
Yes.
Not asking if the springs are on. What is the mechanical timing doing? Is it working, not frozen, and at what rpm?
Yes the springs are on, don't know what the mechanical advance is doing.
Idle problem even when hot? I assume so since you said several tanks of gas.
Yes.
You did use screws to block the vacuum lines. This may, I say may be a problem. store bought caps, round phillips screw drivers or golf tees. Something smooth and something that eliminates the hoses if possible.
Yes I did use screws to block the vacuum lines and it went it tight, not store bought caps or golf tees. Do you think that would make that much of a difference?
You changed carbs so that shouldn't be the problem
Yes and the last carb was rebuit by my son's auto class teacher, the one before was by a mechanic.
Stethascope hose to the intake to head mating area might find a leak.
I have headers with a old rusted exhaust that has to many leaks, I don't think I would hear it over the exhaust noise.
Phil Zell
I moved the weights by hand when I was checking the vacuum advance and it moved freely.
Thanks for all your input.
I'm still trying
Frank
Why exactly do you think you have a vaccum leak?
If I put my hand on the primary or slighly close the choke when the car is up to temperature the idle revs as high as 700 rpm more.
What did you do that started this problem or was it there as far as you know before?
The car has been stored for over 15 years and It was my daily driver before then.
Did it idle before and if it did what was changed since then?
Stored 15 years.
Does your timing change when you rev the engine up to 3000-4000? You don't even need to know the value, just that it does change.
Yes.
Not asking if the springs are on. What is the mechanical timing doing? Is it working, not frozen, and at what rpm?
Yes the springs are on, don't know what the mechanical advance is doing.
Idle problem even when hot? I assume so since you said several tanks of gas.
Yes.
You did use screws to block the vacuum lines. This may, I say may be a problem. store bought caps, round phillips screw drivers or golf tees. Something smooth and something that eliminates the hoses if possible.
Yes I did use screws to block the vacuum lines and it went it tight, not store bought caps or golf tees. Do you think that would make that much of a difference?
You changed carbs so that shouldn't be the problem
Yes and the last carb was rebuit by my son's auto class teacher, the one before was by a mechanic.
Stethascope hose to the intake to head mating area might find a leak.
I have headers with a old rusted exhaust that has to many leaks, I don't think I would hear it over the exhaust noise.
Phil Zell
I moved the weights by hand when I was checking the vacuum advance and it moved freely.
Thanks for all your input.
I'm still trying
Frank
Race Director
Joined: Dec 2004
Posts: 15,025
Likes: 2
Just a quick reply before I head out.....
I have had intakes that developed a crack on the bottom of the manifold, under the baffle plate. Drove me bonkers for a few weeks. You wouldn't be able to see it unless the manifold was off, and the baffle plate was removed. EGR and heat played a part in this happening. Changed manifolds and all was grand.
I gotta go.....I'm late...................
I have had intakes that developed a crack on the bottom of the manifold, under the baffle plate. Drove me bonkers for a few weeks. You wouldn't be able to see it unless the manifold was off, and the baffle plate was removed. EGR and heat played a part in this happening. Changed manifolds and all was grand.
I gotta go.....I'm late...................
Drifting
Joined: Nov 2001
Posts: 1,469
Likes: 6
From: 68 427 4.11s Roadster
Air fuel spark.
Not fuel or spark so just air. Thats assuming nothing internal like rings or such. Could try a compression check and follow it with oil sprayed in the cylinders.
I'm wondering if the exhaust leak could be doing all this? I know that an engine loses all its power and think it does affect idle. Never tried tuning a leaking system though.
My crappy dynasty has a slight exhaust leak and the engine surges when I park. Computer yes but the idle has changed.
I'm thinking the loss of backpressure is really screwing up the intake.
You don't have a vacuum leak but instead the exhaust is preventing a good vacuum.
Only 2 things changed on your car - 15 years of aging and the exhaust is gone.
If you cut the old hoses short and plugged them they might be leaking. New hoses probably would seal though. Try swapping ends since the nipple end takes on a permanant flare.
The only leak I can think of thats left is the intake gasket.
Can you bubba patch the exhaust system just to take it to a garage? Furnace cement will patch exhaust but it won't remake it
This lets you get the new exhaust and then will be a bit more sane standing near it. I still think the exhaust is either part or all of the problem.
Not fuel or spark so just air. Thats assuming nothing internal like rings or such. Could try a compression check and follow it with oil sprayed in the cylinders.
I'm wondering if the exhaust leak could be doing all this? I know that an engine loses all its power and think it does affect idle. Never tried tuning a leaking system though.
My crappy dynasty has a slight exhaust leak and the engine surges when I park. Computer yes but the idle has changed.
I'm thinking the loss of backpressure is really screwing up the intake.
You don't have a vacuum leak but instead the exhaust is preventing a good vacuum.
Only 2 things changed on your car - 15 years of aging and the exhaust is gone.
If you cut the old hoses short and plugged them they might be leaking. New hoses probably would seal though. Try swapping ends since the nipple end takes on a permanant flare.
The only leak I can think of thats left is the intake gasket.
Can you bubba patch the exhaust system just to take it to a garage? Furnace cement will patch exhaust but it won't remake it
This lets you get the new exhaust and then will be a bit more sane standing near it. I still think the exhaust is either part or all of the problem.
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Drifting
Joined: Sep 2003
Posts: 1,325
Likes: 6
From: FRANKLIN GA
Well... It looks like you covered everything except the lower part of the intake gasket, but if you've never pulled the intake this shouldn't be the problem.
Instead of the screws in the hoses, pull them from the carb and intake and go to autozone or somewhere and get a pack of assorted caps and cap everything from the carb and intake and give it another try. With the hoses being 15 years old it might be the hoses themselves leaking somewhere...at least it would take them out of the equasion.
If it still won't idle after everything is capped it will be either a bad EGR valve or a bad gasket... carb or intake...if it ran fine before you stored it
P.S. I know this is a stupid question, but you did put fresh gas in it didn't you???
Instead of the screws in the hoses, pull them from the carb and intake and go to autozone or somewhere and get a pack of assorted caps and cap everything from the carb and intake and give it another try. With the hoses being 15 years old it might be the hoses themselves leaking somewhere...at least it would take them out of the equasion.
If it still won't idle after everything is capped it will be either a bad EGR valve or a bad gasket... carb or intake...if it ran fine before you stored it
P.S. I know this is a stupid question, but you did put fresh gas in it didn't you???
Last edited by EDDIEJ82; Aug 4, 2005 at 08:51 PM.
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,255
Likes: 82
From: Brampton Ont.
nitronick
I tried spraying around the edges of the intake manifold and didn't see any improvement.
Techno
The exhaust leak is only past the headers. When people run open headers on there cars shouldn't the engine still idle?
It won't hurt to replace the vacuum hoses although I'll have to leave that project to the weekend. The car has 50,000 original miles but hey....it's more the years of deterioration.
The problem with taking it someplace to get the exhaust done is the idle has to be at around 1700 rpm in neutral in order for it to idle at around 1200 in drive and it still stalls occasionally cause its a rough idle.
I'll bubba patch the exhaust tomorrow.
EDDIEJ82
I'm going to replace the hoses as Techno suggested and then I'll plug them.
Yes, I did let the car run dry, put the rebuilt carb on with fresh gas.
Thanks again everyone.
It's nice to get a brainstorm of ideas, I'm hopping I missed something, and I'll get this baby idling soon.
Thanks
Frank
I tried spraying around the edges of the intake manifold and didn't see any improvement.
Techno
The exhaust leak is only past the headers. When people run open headers on there cars shouldn't the engine still idle?
It won't hurt to replace the vacuum hoses although I'll have to leave that project to the weekend. The car has 50,000 original miles but hey....it's more the years of deterioration.
The problem with taking it someplace to get the exhaust done is the idle has to be at around 1700 rpm in neutral in order for it to idle at around 1200 in drive and it still stalls occasionally cause its a rough idle.
I'll bubba patch the exhaust tomorrow.
EDDIEJ82
I'm going to replace the hoses as Techno suggested and then I'll plug them.
Yes, I did let the car run dry, put the rebuilt carb on with fresh gas.
Thanks again everyone.
It's nice to get a brainstorm of ideas, I'm hopping I missed something, and I'll get this baby idling soon.
Thanks
Frank
Race Director
Joined: Dec 2004
Posts: 15,025
Likes: 2
The crack I am referring to is on the bottom of the intake. You would have to pull the manifold and remove the splash guard to look for it. I guess that would be a last resort kinda thing, after you have exhausted all other possibilities.
Then explain to me why my racecar has plenty of vacuum with open headers.
I'm wondering if the exhaust leak could be doing all this? I know that an engine loses all its power and think it does affect idle. Never tried tuning a leaking system though.
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Originally Posted by Maymyvetteliveforevr
Exactly......now how do I ( get out and find the leak )? That's my problem nitronick, how do I find it??????
It's so severe that it should be so obvious and easy to locate!
HELP!
Frank
It's so severe that it should be so obvious and easy to locate!
HELP!
Frank
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,255
Likes: 82
From: Brampton Ont.
Check the line to the PCV and make sure it's not cracked. Make sure the check valve in the PCV is working and that it's not a direct vacuum leak into the valve cover.
I installed a new pcv valve and checked the hose for leaks and it was good.
Thanks for the suggestion SanDiegoPaul, I'll try almost anything at this point
Frank
I installed a new pcv valve and checked the hose for leaks and it was good.
Thanks for the suggestion SanDiegoPaul, I'll try almost anything at this point
Frank
Melting Slicks
Joined: Jun 2002
Posts: 2,609
Likes: 1
From: Behind the wheel of a large automobile
Originally Posted by nitronick
Just a quick reply before I head out.....
I have had intakes that developed a crack on the bottom of the manifold, under the baffle plate. Drove me bonkers for a few weeks. You wouldn't be able to see it unless the manifold was off, and the baffle plate was removed. EGR and heat played a part in this happening. Changed manifolds and all was grand.
I gotta go.....I'm late...................
I have had intakes that developed a crack on the bottom of the manifold, under the baffle plate. Drove me bonkers for a few weeks. You wouldn't be able to see it unless the manifold was off, and the baffle plate was removed. EGR and heat played a part in this happening. Changed manifolds and all was grand.
I gotta go.....I'm late...................
Michael
Race Director
Joined: Dec 2004
Posts: 15,025
Likes: 2
Since you have checked everything external(and replaced most of it! 
), I think it's time to start considering looking at internals.
What do the plugs look like(assuming they have been run for a bit)? Oily? Time to look at the lower parts of the intake gaskets. Don't forget to check the underside of the manifold for a crack as I said earlier. With 9 to 10 inches of vacuum, I am leaning toward a crack.
), I think it's time to start considering looking at internals. What do the plugs look like(assuming they have been run for a bit)? Oily? Time to look at the lower parts of the intake gaskets. Don't forget to check the underside of the manifold for a crack as I said earlier. With 9 to 10 inches of vacuum, I am leaning toward a crack.
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,255
Likes: 82
From: Brampton Ont.
75Rag,
Thanks for the offer, I'll keep that in mind, I may have a spare intake, but forgive me for trying to keep it original as possible.
nitronick
I'll take a look at the plugs once the motor cools down. I checked vacuum pressure and at idle it's at 11 psi. Does anyone know what it should be for a 75 L48 with 10:1 comp?
With 9 to 10 inches of vacuum, I am leaning toward a crack.
nick, I'm not sure where you got that figure since I hadn't checked vacuum presure until now.
Thanks
Frank
Thanks for the offer, I'll keep that in mind, I may have a spare intake, but forgive me for trying to keep it original as possible.
nitronick
I'll take a look at the plugs once the motor cools down. I checked vacuum pressure and at idle it's at 11 psi. Does anyone know what it should be for a 75 L48 with 10:1 comp?
With 9 to 10 inches of vacuum, I am leaning toward a crack.
nick, I'm not sure where you got that figure since I hadn't checked vacuum presure until now.
Thanks
Frank
Race Director
Joined: Dec 2004
Posts: 15,025
Likes: 2
Uh.....your first post.
WHAT I'VE DONE: Installed rebuilt quadrajet carb, new plugs, wires, cap, rotor, fuel filter, PCV, pinched every possible vacuum line on intake, sprayed water and/or brake cleaner all over intake and vacuum lines to see if there was a change in RPM, plugged vacuum lines to headlights.
OVERALL RESULT---NO CHANGE. Present vacuum pressure is 9-10 lbs. Timing has been set. I'm losing hope and have all but given up. HELP!!!
OVERALL RESULT---NO CHANGE. Present vacuum pressure is 9-10 lbs. Timing has been set. I'm losing hope and have all but given up. HELP!!!
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,255
Likes: 82
From: Brampton Ont.
I stand corrected nitronick, I apologise, I checked my notes and 2 months ago when I checked it, it was between 9 and 10. I guess by playing around with it I got it to around 11.
Thanks for correcting me.
Frank
Thanks for correcting me.
Frank