Tips for locating an exhaust leak

Discussion in '80-Series Tech' started by 96r50, Mar 25, 2009.

  1. 96r50

    96r50

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    I think my truck has an exhaust leak. There is a buzzing type noise that increases with RPM. I can't hear it with the windows up, but with the windows down on a quiet street or while driving by a wall I can hear the buzzing. The noise is louder/more pronounced when the engine is under load (accelerating in gear) than when I rev it in park.

    I have replaced the manifold to downpipe gaskets and both catalytic converter gaskets. I have yet to replace the O2s and associated gaskets, or the muffler to resonator gasket. The noise seems to be coming from the front half of the truck though, so I don't suspect that last one. Heat shields are tight, bellhousing-to-downpipe clamp is snug, no broken exhaust mounts that I can find, and no visible contact points on the frame or sliders.

    My first suspicion is an exhaust leak, but I am having a hard time determining if there are any leaks. What methods do you use to find exhaust leaks? Feathers, flames, high priced sniffers?

    The second option is that it is not an exhaust leak. At this point I'm running out of other ideas for the source of this sound. I read Doug's post a week ago about the aircleaner tube rattling against the fender, but I've played around with that to no avail. Other ideas would be welcome at this point.
    :cheers:
     
  2. toy4xfun

    toy4xfun

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    hey i am new here but try this the first part is very important put on a welding glove (don't ask) then cover your tail pipe if there is a leak it will not blow your hand off the pipe and even better you will hear it if you do not use the welding glove you will have to hold a cold beer in your hand that you used to cover the tail pipe for 1 to 4 hours and trust me that does work it won't even blister
     
  3. toy4xfun

    toy4xfun

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    if it is not exhaust do you have a roof rack none stock that is it als could be that
     
  4. Lka1988

    Lka1988 Wheeling in scale

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    x2, except I'd use a rag to plug the tail pipe. Have a buddy help you out on this, since the resulting back pressure would blow out the rag.
     
  5. john_eckels

    john_eckels SILVER Star

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    I had the same buzzing sound. I had a bad O2 sensor gasket and a small crack at the Y in the Y pipe.
     
  6. BAILEIGH INC

    BAILEIGH INC

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    Ha Ha
     
  7. rove_mcanus

    rove_mcanus

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    the ghetto back yard trick in my shed is to pour some brake fluid down the intake. If you have a leak, you'll see the smoke coming out of it.
     
  8. 96r50

    96r50

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    Hmm, I hadn't thought of the plugging the tailpipe method. I'll have to give it a shot. I was thinking about using some Seafoam to create lots of smoky white exhaust.
     
  9. Skrewball

    Skrewball TLCA#18502 SILVER Star

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    have a friend plug the tail pipe with a glove or rag in little intervals(15 sec each) while you listen for the noise. using your hand carefully feel around suspected area for exhaust.

    other way is to look in suspected areas for a little black spot. usually when there is a leak, it will cause the surrounding area to turn black(like the rear bumper of some POS tuner car)

    my vote would be the O2 sensors
     
  10. acflyguy18

    acflyguy18

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    I found my using seafoam, just a fortunate side effect in my case.
     
  11. 96r50

    96r50

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    I just drove the truck again tonight down a quiet side street and the noise is definitely pronounced when the engine is under load (accelerating). It was not noticeable at all while coasting. I'm starting to think one (or more) of the O2 nuts are loose and the higher RPM/engine load is enough to force exhaust past the gasket(s). I'll try and get a good look at them in the next few days.

    If it's not the exhaust, any ideas as to what loose parts would cause this type of vibration/buzzing noise only while under load?

    Thanks for the help thus far!
     

  12. Michael Hanson

    Michael Hanson

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    Soapy water in a spray bottle. Mike
     
  13. nycmatt

    nycmatt

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    I just purchased a 94 LC and have the same problem. Did you ever figure out what the problem was and how to fix it?

     
  14. 96r50

    96r50

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    Unfortunately I haven't had a chance to really look at it. Between exams and the ground being covered in snow I haven't had much inclination to crawl under there and take a look. I might get to it this weekend. I'll post up if I find anything conclusive.
     
  15. The Lovely Boyo

    The Lovely Boyo

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    My exhaust was causing the truck to fail its emmissions test a couple of months back, but the leak was very difficult to locate - very quiet.

    It was under the stainless steel cover of the front cat.

    I had to remove the downpipe (cat attached) and peel the stainless cover off the cat (go carefully). I could then see the large rusty lump of cat that the cover had been holding in place. So now I had a nice hole in the cat instead.

    Great fun trying to weld rust, aye!

    Prior to refitting I also filled the pipe with water to make sure the leak was properly sealed (it wasn't lol).

    Passed its test OK afterwards though.
     
  16. e9999

    e9999 You want to do what...? Moderator

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    you could also use a cylinder leak down tester or the redneck version of that?

    (or go from the exhaust pipe but that'll take some fabbing)
     
  17. lowenbrau

    lowenbrau SILVER Star

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    You can use compressed air to find the leak. Put a valve on the end of the airhose so it just hisses and then, with the rig running. blow air all over the manifolds, pipes, mufflers, cats, etc... The hissing sound changes drastically when you hit the leak. You can do the same thing with a oxy-acetylene torch as well. It can be easier to get into difficult to reach areas.
     
  18. 98 SNAKE EATER

    98 SNAKE EATER

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    Block the tailpipe on a cold morning start and the steam will exit from your leak :idea:
     
  19. 96r50

    96r50

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    Found it! Over the Easter weekend I had my brother plug the tailpipe with a blanket while I crawled around under the exhaust. With the exhaust plugged the leak was really simple to locate: the joint between the first and second cat. I replaced these last summer, but it appears that the gasket is not thick enough to bridge the gap. My plan is to try using two gaskets. Yay or nay?

    Thanks for all the tips!
     
  20. Atticus

    Atticus

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    I say double the gasket, and then wrap the joint in exhaust tape.
     

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