Boost leak or plugged cats
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Audiworld Junior Member
Joined: Dec 2013
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Boost leak or plugged cats
2002 A6 2.7t Quattro.
I think I have a boost leak and or plugged cats. What are your thoughts???????
Here is what the car is doing. When I accelerate the car stalls/hesitates/jerks at about 3000 rpm and will not speed up I can here a hissing/whistling/venting sound. If I try to lightly accelerate or use the cruise control to raise the speed I can get up to speed also if I down shift and keep the rpm's up it will make power but you can hear what I think is a boost leak. I used the fogger we have at work to find two leaks in the intake system. One was intake "y" boot and passenger boost sensing line to the turbo. (Not sure how long the banjo not has been missing) both fixed. (Car was parked and not used for several months it had ECM issues.) Was planning on using the fogger again to see if I have more leaks. If I can take it home.
Why I also suspect cat is very poor gas mileage and does not seem to have power.
Thanks in advance for any help.
I think I have a boost leak and or plugged cats. What are your thoughts???????
Here is what the car is doing. When I accelerate the car stalls/hesitates/jerks at about 3000 rpm and will not speed up I can here a hissing/whistling/venting sound. If I try to lightly accelerate or use the cruise control to raise the speed I can get up to speed also if I down shift and keep the rpm's up it will make power but you can hear what I think is a boost leak. I used the fogger we have at work to find two leaks in the intake system. One was intake "y" boot and passenger boost sensing line to the turbo. (Not sure how long the banjo not has been missing) both fixed. (Car was parked and not used for several months it had ECM issues.) Was planning on using the fogger again to see if I have more leaks. If I can take it home.
Why I also suspect cat is very poor gas mileage and does not seem to have power.
Thanks in advance for any help.
AudiWorld Senior Member
Joined: Mar 2004
Posts: 911
Likes: 17
I would test for boost/vacuum leaks again, since you hear the leak under power. You need to get car raised to check turbo plumbing under car. Look for broken hose clamps.
Could be a combination of things. You also could have bad spark coil or coils and you need to scan with VCDS to see what's going on. If a whole bank is missing, bad spark control module.
Unplug MAF sensor and see what happens. If engine runs better unplugged, suspect MAF sensor.
Google cat test. You can do pre and post cat pressure readings to check for blockage.
Could be a combination of things. You also could have bad spark coil or coils and you need to scan with VCDS to see what's going on. If a whole bank is missing, bad spark control module.
Unplug MAF sensor and see what happens. If engine runs better unplugged, suspect MAF sensor.
Google cat test. You can do pre and post cat pressure readings to check for blockage.
Thread Starter
Audiworld Junior Member
Joined: Dec 2013
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So I found another leak on the driver side Bi pipe going from the intercooler to the throttle body boot (boot was replaced about one year ago but car has been parked most of that year ). I am going to seal the boot and the intercooler and look for more leaks.
Last edited by wshymas; Mar 18, 2018 at 03:36 PM.
AudiWorld Senior Member
Joined: Jan 2015
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From: Sierra Vista, AZ
Pretty common problem. Going clear back to the '80s this issue would crop up. My '85 5000S was running fine and I stopped at a convenience store. Came out five minutes later and the car wouldn't start. Essentially the same hose developed a crack. These things are almost impossible to find sometimes.
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No it was not easy to track down. I could see the smoke but not where it was leaking from. Had to jack the car up and look up to see it seeping out of the seam. After I removed the pipe I did plug the boot and intercooler and rechecked and did not see anymore smoke. Fingers crossed. Looking on ECS, Ebay even Amazon to see what options I have for replacement parts.
Last edited by wshymas; Mar 18, 2018 at 03:37 PM.
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AudiWorld Senior Member
Joined: Jan 2004
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From: Ocean Isle Beach NC
That TTB can be a bugger. Cracks and splits you cannot detect until removed and in your hands under a bright light. The clamp that secures it can be over tightened and ruin a new boot. Or a boot that is not completely on can look good and still leak. I had a small hose maybe only .3 inch dia in the back under the intake that was split. Obviously could not see this until removed. Small crack but big effect. Many on here recommend replacing all hoses on a car this age. Won’t know what you will find until you do them.
AudiWorld Senior Member
Joined: Jan 2015
Posts: 1,186
Likes: 43
From: Sierra Vista, AZ
Don't know your location but check AutohausAZ.com also. Good prices and service. Some OEM parts as well as after market. I have heard of others that basically replaced all the soft intake hoses based on age of the vehicle.