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View Full Version : Low Vacuum- Not a leak!(complete run down)



Auddii
02-28-2013, 11:49 AM
I have been dealing with a vacuum issue for as long as I can remember with my car. I pretty much bought a lemon just to get that out of the way up front. I have replaced the turbo, and head gaskets since buying it last December 2011. I just got finished with the leaking head gasket and have decided to tackle this vacuum/shit idle issue.

I have pressure tested the system. There were no leaks. I pressure tested again. Still no leaks. Short of getting it smoke tested I can't find a leak. Is there part of the system I'm not pressurizing?

When I had the head off I had the machine shop check it out and check the valves. Short of taking the valve train apart the guy said it looked fine. The compression is also good on the engine though I have never done a leak down test.

The codes I have now are 1. Lean mix and 2. brake boost vacuum pump failure. The second one I think I tracked down to a faulty brake booster vac pump which I have since my car is tiptronic.

The only thing that I know is wrong right now is my cam chain tensioner is going out. It makes a tapping noise that is beyond annoying. There's no code for this but can it cause low vac readings if the cam chain is loose?

I have vag com I will test anything that anyone thinks is worth checking on and am open to anything seeing as this has been an on going issue for me.

Wraith600
02-28-2013, 11:54 AM
Audii, read my on going thread in regards to the lean code. Pointing at fuel filter and / or MAF sensor for me.

http://www.audizine.com/forum/showthread.php/527722-The-P0411-and-P1128

Auddii
02-28-2013, 12:06 PM
Fuel filter I replaced and I did a maf log but I forgot about it. Ill post that up probably tonight.

98A4TurboAWD
02-28-2013, 03:57 PM
The only time I had low vacuum on a car with no leaks it turned out to be a timing issue. That was a car that had an adjustable distributor though, and I was able to just put a timing light on it and fix it.

If you have no leaks and everything outside of the engine is functioning properly, then the only things that come to my mind as causes are:

Timing not correct
Aftermarket cam
Low idle

My Camaro has an aftermarket cam and the idle turned down to like 800rpm and the vacuum is very low, around 17", down from about 25" when factory.

jvega21
02-28-2013, 04:12 PM
any exhaust leaks? those could cause lean mix codes as well. my leak was at the cat/downpipe connection. one bolt wasnt tight enough

Auddii
02-28-2013, 06:09 PM
I know I have an exhaust leak at the flex pipe. I just did the timing belt with the head gasket so timing should be right. No after market cams either.

Auddii
02-28-2013, 07:05 PM
I just had a thought. I have that code for the brake booster. I always assumed it was the pump that was bad but is it possible for there to be a leak in the booster itself that I can't hear when I pressure test the system?


Edit- Never mind that I actually know the booster is holding pressure because it will still hiss if you pull the vac line days after running the car.