Tips for finding an exhaust leak
 

Ok guys I need your help on this one. I'm wondering if you guys have any cool tips or tricks to finding an exhaust leak. I recently installed my FI headers, and there's a loud hiss sound coming from somewhere near the passenger side O2 sensors. I can't pinpoint the location exactly. So far I've tried using a stethoscope and a smoker machine. The smoker uses baby oil to produce a vapor which it then pumps through the muffler into the exhaust system while you block everything else off. We pumped at about 7lbs pressure and found a few tiny leaks, but the sound is still there. I have checked every bolt and everything seems to be tight. I'm gonna try putting some sea foam in the intake manifold and see if I can find something that way. Do you guys have any other suggestions? This sound is driving me nuts, so I really appreciate any help you can give.


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Rubber gloves and seal your hands around the area that you suspect is leaking???

Here is a quick vid I made on a how to create a stethascope. I know you said you tried it, but maybe it might help.

https://www.youtube.com/watch?v=G507...s&feature=plcp

You can here a mouse fart with this thing.

That might work normally, but if I could feel it with my hands then I'm sure the smoke we used would have seeped out without a problem.

Thanks for the vid, I'll check it out :tup:


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Is that a copper tube or rod?


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Are you talking about the hiss on deceleration?

There is that, but it also makes the same noise on acceleration, and the harder I accelerate, the louder it gets.


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copper tube from home depot

FWIW - I used a 3 foot piece of garden hose to find where an idler bearing whine was coming from on the wife's Buick a while back. Read about it on some auto repair thread, was hesitant at first but sure as sh*t, it really worked well.

Hold one end next to your ear and put the other end at your suspect locations, if they are the same sound those are probably not leaking, the leaker will be pretty obvious I bet with the hose.

Good Luck - Let us know how it goes.

Awwwww Huck!!!! I hope you get it fixed.

Haha thanks Zgirl, me too! I'm taking it to my buddy's shop tomorrow to put it on the lift and try the sea foam. Thanks fire hawk and rhd for the info. I'll try that out if this sea foam doesn't work :(


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let us know how it turns out

Will do!


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To find an exhaust leak you could just run seafoam through one of your vaccum lines (brake booster line). Any leaks will spit out white smoke. Do this on my other cars to clean out vaccum lines. Your exhaust will be thick and white for a few minutes.

As far as making a stethescope, I just use a piece of plastic hose to tune the carbs on my 1960 morgan. hold one end to ear and the other to carbs - you can hear them hissing pretty well that way. The owners manual for it actually says to do that.

I Just bought some sea foam for that exact purpose, but the problem is that I don't know crap about vacuum lines, so I don't know which one to use. Is there any way you could take a pic of the hose I need to put in the sea foam? I would really appreciate it.


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i cant believe no one else has said this. you dont have an exhaust leak. its simply the engine hissing. look it up. "vq37 hiss"

its simply a byproduct of removing the factory catalytic converters. its there when you replace with test pipes, highflow cats..long tube headers. you name it. the ARK high flow cat's attempt to fix this with a resonant chamber. look it up!

heres the ARK HFC's:
http://www.the370z.com/exhaust-intak...-370z-g37.html

The op mentioned in post #7 that he was getting it on acceleration also, which is not typical when referring to new exhaust hiss.

I personally don't feel it's an exhaust leak, but from the OP's description, it sounds like it is not the typical post-cat removal hiss.

Hopefully he will figure it out and give us an update.

This is the best video i can find for seafoam
instructions for seafoam (break booster) - YouTube

I have yet to do it on a 370 but it should be the same concept. There should be a large vaccum line running into your brake booster. Disconnect the line from the brake booster while your car is running. Your engine speed should drop and the car will try to die unless you hold your finger over the hole in the vaccum line. As a friend keeps the gas pedal slightly depressed (so the car won't die) remove your finger from the end of the vaccum line and either pour seafoam into the brake line or stick the end of the vaccum line into a container containing the seafoam. Apply enough accelerator to keep the car from dying. After about 1/3 of the can of seafoam is sucked up, reconnect the vaccum line and continue to let the car idle until no smoke is seen out of the back. There will be copious amounts of thick white smoke behind the car.

I take no responsibility if somehow this messes up your car. Even though it's a petroleum product I'm not sure if it is possible to hydrolock an engine or damage some weird engine this way. I use seafoam all the time on my 240 and morgan.

I know the sound you're talking about, and I don't believe this is the same thing. I heard it a little bit when I had just the CBE installed, and I was expecting that. This is apparent all the time, especially when I gas it. It's so loud right now that I seriously sound like I'm turbo'ed. Unfortunately I've been really busy with work and side jobs the last few days, so I haven't been able to mess with it. I'll keep you guys updated :tup:


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Thank you Read! I appreciate this info, I'll let you know what I find :)


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i have a high pitched hiss on acceleration. sounds like a rock in a tin can. this is also attributed to the HFC. look it up!

Yeah but I don't have hfc's, I have long tune headers. Also, since I pulled my exhaust apart and put it back together, the sound has gotten louder. That wouldn't happen if it was a normal thing.


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HFC's, long tube headers. same thing noise wise. your long tube headers essentially delete the stock cat, therefore the noise is ALOT louder.

whenever you remove the stock cat's you will hear rasp. there is absolutely nothing you can do about it

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RASP ^

Yeah I definitely know what rasp sounds like, that's not what this is. When I'm stepping in the gas it sounds like SSSSSSSSSSSSSSSSSSSSSS and then I let off and it's like shshshshshshshsh... Hopefully you can hear it in this...

http://i62.photobucket.com/albums/h9...t/ca3d7036.mp4


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And also let me pony out that I have heard another persons car that was the same exact setup as mine. 09 Z stillen cai, FI lth/cbe non res'd, and he didn't have this sound at all.


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Well the guys working for the gas company spray some soapy water on the leak area. If you have a leak, it will blow bubbles. Saw the guy do this on my gas meter leak, i could smell gas but could not tell where it was coming from, meter or line coming in. Sure enough we saw the bubbles. I think they mix dishwashing liquid and water. You could also just spray some kids bubbles on it.

I will be sure to do that. Thanks for your input.

I did the seafoam today (thanks again to read for the detailed instructions!) and found a leak where my headers meet the connecting pipe to the X-pipes, so I got a new gasket, waiting for it to cool down to install.


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Can't you use soapy water and a spray bottle?

That was going to be my suggestion but it sounds like he found his leak.

I did find A leak, between the headers and the next pipe on the driver side. The gasket wasn't sitting right. I loosened it up and adjusted it then tightened it back up. But it hasn't fixed the sound totally. I'm starting to wonder if it's SUPPOSED to sound like that. I mean, I heard the hiss that the catback would make when I would rev it a bit and then let off the gas. When the rpms were going down it would hiss just for a second, and it was pretty quiet. But this is very loud, loud enough to hear it with the windows up and over low music. It sounds like I have a turbo setup. I made a video of the sound while my mother in law was revving the motor a little bit. Again, I know it makes a sound when you let off the gas, that's normal. But imagine this sound all the time, accel, decel, cruising, everything.

http://i62.photobucket.com/albums/h9...C1E0BD22C2.mp4


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alright guys, this is the last video I'll post, since I pretty much have my answer now. I talked to a couple of guys who have the same exact exhaust as me and they don't have the hissing sound on acceleration like I do, so I'll probably take it to a shop to get fixed up with new gaskets and all that. You can hear it when I step on the gas...

Hey Huck. Did you ever find a full solution to the leak?

Just now saw this last question, turns out I fixed the leak but the sound is still there, it's the natural "VQ hiss" that is common with our cars. Tony from Fast Intentions gave me a really smart technical answer that I promptly forgot as to what caused the sound, something about thinner pipe walls creating a resonant harmonic frequency or something, all I know is that it's normal and too be expected.


I survived Zdayz 2013

(barely)