Massive vacuum leak?
Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,193
Likes: 381
From: Lunenburg MA
Massive vacuum leak?
OK, I know this is a stupid question, but I'm gonna ask it anyways. I can completely block the throttle body intake on my '87 and the engine will keep running. That's not normal, right? Actually it runs better. The ECM says lean and the new O2 sensor sits around 180MV (no cross counts) even with it blocked.
Massive intake leak, right? I know that makes sense, but I was so careful putting together and I've been doing this stuff for a lot of years. All the ports are connected. Idle is constantly seeking and vacuum goes from 8 to 15 or so as it seeks.
Fuel pressure is prefect. All injectors are new and all are firing. All cylinders have excellent compression and are all plugs are firing. Timing is dead on and the firing order is right. New MAF, no errors from the ECM other than "lean".
Vacuum leak, has to be, right?
Thanks for reading!
Massive intake leak, right? I know that makes sense, but I was so careful putting together and I've been doing this stuff for a lot of years. All the ports are connected. Idle is constantly seeking and vacuum goes from 8 to 15 or so as it seeks.
Fuel pressure is prefect. All injectors are new and all are firing. All cylinders have excellent compression and are all plugs are firing. Timing is dead on and the firing order is right. New MAF, no errors from the ECM other than "lean".
Vacuum leak, has to be, right?
Thanks for reading!
Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,193
Likes: 381
From: Lunenburg MA
Thanks for the ideas!
Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,193
Likes: 381
From: Lunenburg MA
Instructor
Joined: Feb 2014
Posts: 139
Likes: 0
From: Lakeland FL
Another thing to check. Does the car still have the EGR valve?
It's possible to have a piece of carbon or other junk stuck in it holding it open. You will have to pull the valve to check.
Also is the right vacuum line going to it? If it has the wrong line going to it it's possible the vacuum is holding it open. To check just pull the vacuum line off.
Good luck
It's possible to have a piece of carbon or other junk stuck in it holding it open. You will have to pull the valve to check.
Also is the right vacuum line going to it? If it has the wrong line going to it it's possible the vacuum is holding it open. To check just pull the vacuum line off.
Good luck
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Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 414
From: WV
If you can't find the leak any other way, you may have to use the "old method" for checking for vacuum leaks.. You can use a propane torch or a can of carb cleaner, but you have to be careful..
..You have to spray this at all the gasketed connections in the top end of the motor ( stay away from hot exhaust pipes)....If you have a vacuum leak, and you spray this near the vacuum leak, you will hear an increase in rpms..This will let you pinpoint where the leak is...I have used this method many times with no problems , but like I mentioned, you do have to be careful because your working with a flammable liquid or gas..
Some guys say to use the gas from a propane torch to check for leaks, I have never used this method but quite a few on here have......WW
..You have to spray this at all the gasketed connections in the top end of the motor ( stay away from hot exhaust pipes)....If you have a vacuum leak, and you spray this near the vacuum leak, you will hear an increase in rpms..This will let you pinpoint where the leak is...I have used this method many times with no problems , but like I mentioned, you do have to be careful because your working with a flammable liquid or gas..Some guys say to use the gas from a propane torch to check for leaks, I have never used this method but quite a few on here have......WW
Last edited by WW7; Mar 30, 2014 at 09:07 AM.
Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,193
Likes: 381
From: Lunenburg MA
If you can't find the leak any other way, you may have to use the "old method" for checking for vacuum leaks.. You can use a propane torch or a can of carb cleaner, but you have to be careful....You have to spray this at all the gasketed connections in the top end of the motor ( stay away from hot exhaust pipes)....If you have a vacuum leak, and you spray this near the vacuum leak, you will hear an increase in rpms..This will let you pinpoint where the leak is...I have used this method many times with no problems , but like I mentioned, you do have to be careful because your working with a flammable liquid or gas..
Some guys say to use the gas from a propane torch to check for leaks, I have never used this method but quite a few on here have......WW
..You have to spray this at all the gasketed connections in the top end of the motor ( stay away from hot exhaust pipes)....If you have a vacuum leak, and you spray this near the vacuum leak, you will hear an increase in rpms..This will let you pinpoint where the leak is...I have used this method many times with no problems , but like I mentioned, you do have to be careful because your working with a flammable liquid or gas..Some guys say to use the gas from a propane torch to check for leaks, I have never used this method but quite a few on here have......WW
Racer
Joined: Dec 2012
Posts: 347
Likes: 25
From: Rockford Illinois
I found a huge vacuum leak on my 1985 by tracing the hose from the PCV valve to where it connects to the pipe that goes into the intake. At the intake the rubber that surrounded the pipe was old and loose so I put a small zip tie around it. It's on the area you described along the drivers side head, if you listen there you will probably hear it sucking air. My car had a wild idle and would always cut off when stopped and after the zip tie was put on I have had a perfect steady idle and no problems.
Thread Starter
Melting Slicks
Joined: Jan 2014
Posts: 2,193
Likes: 381
From: Lunenburg MA
I found a huge vacuum leak on my 1985 by tracing the hose from the PCV valve to where it connects to the pipe that goes into the intake. At the intake the rubber that surrounded the pipe was old and loose so I put a small zip tie around it. It's on the area you described along the drivers side head, if you listen there you will probably hear it sucking air. My car had a wild idle and would always cut off when stopped and after the zip tie was put on I have had a perfect steady idle and no problems.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
I made the mistake of putting on a 1/2" hose and it seemed OK at first but got loose and starting leaking after a while.