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Old 03-23-10, 02:48 AM   #1
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Effects of an exhaust leak?

Okay, so after replacing my downpipe and cat converter I noticed that there's a leak coming from the turbo area (which is probably the turbo to manifold or manifold to engine gasket). Would this leak cause my car to idle rich? I just need some clarifying because I'm thinking of getting a PFC to help me pass smog...since I failed for idling way too rich or would I just be wasting money for something that might be a simple fix?
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Old 03-23-10, 09:52 AM   #2
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If enough exhaust gas is leaking out or enough or enough fresh air is getting in that could throw off the O2 sensor's readings which will change the idle and light load mixtures in a car with a stock ECU.

Really, the question is why haven't you fixed the exhaust leak? It's a problem, fix it. It's not going to get better or go away.

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Old 03-23-10, 11:22 AM   #3
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Quote:
Originally Posted by DaleClark View Post
If enough exhaust gas is leaking out or enough or enough fresh air is getting in that could throw off the O2 sensor's readings which will change the idle and light load mixtures in a car with a stock ECU.

Really, the question is why haven't you fixed the exhaust leak? It's a problem, fix it. It's not going to get better or go away.

Dale
Totally agreed with Dale here. Exhaust leak infront of O2 = more air into the exhaust and will affect O2 reading. (Extra O2) ECU would compensate for that extra air in the system which will result in extra fuel added to the combustion chamber. Therefore you will get more fuel and runs more rich.

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Old 03-23-10, 02:48 PM   #4
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Thanks for the info I want to fix it but been really busy with school and work. I've also been trying to decided whether I want stock gaskets or the graphite ones that pineapple sells...what do you guys run or use when you change your turbo gaskets?
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Old 03-23-10, 09:37 PM   #5
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to me, the updated metal oem mazda ones look almost indestructible. i used these when i did my turbos. rather expensive though....

if you were talking about internal gaskets and such, my bad i misunderstood ya.
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Old 03-24-10, 12:26 AM   #6
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okay, a little update so I took everything off and checked all my gaskets and they were all fine, no cracks on the manifold, even checked my intake manifold gaskets and they were okay too...i'm gonna put everything back on and see if it stills sounds like it's leaking.
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Old 03-24-10, 12:47 AM   #7
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To be honest, I think that most rotaries will sound like they have an exhaust leak. idk why, but I sent my FD off to two different exhaust shops. One of them completely redid my exhaust for me and siliconed the **** out of it and it still sounded like there was an exhaust leak.

I also looked at Bewtew's video of his exhaust and his sounded the same way mine did.
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Old 03-25-10, 02:39 AM   #8
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thanks, for the heads up...after i put everything back on and it still sounds like that then I'm just gonna leave it like it is
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Old 03-27-10, 03:01 AM   #9
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well it still sounds like an exhaust leak, drives like one too...iono i'm thinking it might be the downpipe cause with the stock downpipe it didn't make this noise.
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Old 03-27-10, 09:47 AM   #10
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Some thin-wall stainless downpipes will have a "ping" noise to them.

With the car bone cold in the morning, get it up on jackstands and start the car. Feel around the exhaust flanges, if there's an exhaust leak you can feel the exhaust spitting out and hitting your hand. Obviously you have to go quick as it will heat up to uncomfortable levels fairly quickly.

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Old 03-27-10, 10:49 AM   #11
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when i put my downpipe on, it had a leak also. tried 3 times sealing it and it wouldnt work. finally ended up taking it off, getting some feeler gauges and a plate of glass and checked to see how far out it really was. Turns out it was so far out that i spent 2 hrs filing it down with various differnt files, but i got it down to .005. put it back on and havnt had a problem since.
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Old 03-27-10, 01:30 PM   #12
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I've had several low mile twin turbo assemblies on my car and both had unfixable leaks where the actuator door pivot rods go through the housings. Some gas will always escape because there is no seal there and it is a clearance fit.

Quote:
Originally Posted by AzEKnightz View Post
Totally agreed with Dale here. Exhaust leak infront of O2 = more air into the exhaust and will affect O2 reading. (Extra O2) ECU would compensate for that extra air in the system which will result in extra fuel added to the combustion chamber. Therefore you will get more fuel and runs more rich.

-AzEKnightz
It's actually a matter of less exhaust gas reaching the sensor rather than more outside air. Outside air can't make it into the exhaust because of the pressure difference.

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One of them completely redid my exhaust for me and siliconed the **** out of it and it still sounded like there was an exhaust leak.
There's your problem right there. Silicone burns up after a few seconds at those temps. That **** blows right out of the flange after that. Good gaskets and flat flanges are the only fixes.

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Some thin-wall stainless downpipes will have a "ping" noise to them.

With the car bone cold in the morning, get it up on jackstands and start the car. Feel around the exhaust flanges, if there's an exhaust leak you can feel the exhaust spitting out and hitting your hand. Obviously you have to go quick as it will heat up to uncomfortable levels fairly quickly.

Dale
Ok, this is really shade tree , but it's worked for me. After it's hot, you can put a feather or a piece of yarn/string on the end of a stick and move it around all the flanges. You'll easily be able to see it being moved by escaping gas and won't burn your hands.
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Old 03-27-10, 02:08 PM   #13
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i've already checked for leaks by hand and can feel nothing...but sometimes when it's cold on start up and I rev it a little there's very little smoke coming from the turbo area but can't seem to find it...i'll just keep checking to see if i can find it, or maybe i'll just change to single turbo...
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Old 03-27-10, 03:58 PM   #14
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Quote:
Originally Posted by alexdimen View Post
It's actually a matter of less exhaust gas reaching the sensor rather than more outside air. Outside air can't make it into the exhaust because of the pressure difference.
Have you personally tried using a gas analyzer and see the result when there is an exhaust leak? What happens to O2 readings?

I can tell you that IT does get through and IT WILL affect O2 reading.

I am not trying to be defensive here, but personally from experience with my exhaust manifold gasket all rusted due to age and heat etc, there was an exhaust leak.

I was lucky enough that I was doing smog class at the time and I was able to put on the smog machine to measure exactly what those readings were about 2 years ago.

Before fix, I had about 2% air leaking through the exhaust gasket. After the replacement of my exhaust manifold gasket (before O2) and I was curious as to the differences of the gasket would make.

So, I decided to put it on the machine and have it analyze the readings again.

Result came out just as expected. O2 reading down to 0.1% and the car was combusting all gas and less HC was measured at the pipe and CO2 level (the quality of a combustion went from about 13.4% - about 14.2%.

Hopefully this help supported my statement

"Exhaust leak infront of O2 = more air into the exhaust and will affect O2 reading. (Extra O2) ECU would compensate for that extra air in the system which will result in extra fuel added to the combustion chamber. "

-AzEKnightz
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Old 03-27-10, 07:10 PM   #15
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shop vac trick

another way to find a exhaust leak is to use a shop vacuum in reverse (blower side). place the hose in the exhaust tip, seal it up with duct tape. get a bottle of soapy water, i prefer a few drops of dawn dishwashing soap. start spraying all the flanges and watch for bubbles.
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Old 03-28-10, 01:19 AM   #16
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^^^^lol...i think i'll try that I've never heard of that before but sounds interesting. I'm also waiting for my boost leak tester, because I believe i have a boost leak somewhere since it's boosting weird-ish...
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Old 03-28-10, 02:30 PM   #17
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Quote:
Originally Posted by AzEKnightz View Post
Have you personally tried using a gas analyzer and see the result when there is an exhaust leak? What happens to O2 readings?

I can tell you that IT does get through and IT WILL affect O2 reading.

I am not trying to be defensive here, but personally from experience with my exhaust manifold gasket all rusted due to age and heat etc, there was an exhaust leak.

I was lucky enough that I was doing smog class at the time and I was able to put on the smog machine to measure exactly what those readings were about 2 years ago.

Before fix, I had about 2% air leaking through the exhaust gasket. After the replacement of my exhaust manifold gasket (before O2) and I was curious as to the differences of the gasket would make.

So, I decided to put it on the machine and have it analyze the readings again.

Result came out just as expected. O2 reading down to 0.1% and the car was combusting all gas and less HC was measured at the pipe and CO2 level (the quality of a combustion went from about 13.4% - about 14.2%.

Hopefully this help supported my statement

"Exhaust leak infront of O2 = more air into the exhaust and will affect O2 reading. (Extra O2) ECU would compensate for that extra air in the system which will result in extra fuel added to the combustion chamber. "

-AzEKnightz
I admit I'm nitpicking to begin with, but this subject could be important in certain situations.

Here's my problem with it. I don't think air is getting into the exhaust. In order for this to happen, the pressure in the exhaust would have to be lower than the outside. Not the case as far as i know.

Your o2 readings were high. You believe it's because air was getting into the system.

Oxygen is a component of the exhaust gases. I believe that because less exhaust gas was getting to the sensor, the sensor saw less oxygen. Then, to correct the low oxygen reading (a simulated rich condition), the computer leans out the mixture, therefore more oxygen exists after combustion, creating high o2 readings on your analyzer.

Fixing the problem allowed all of the exhaust gasses to reach the sensor, therefore all of the oxygen existing after combustion was registered by the computer. The computer no longer leaned out the mixture because of this.

The system operates on the assumption that all of the gas exiting the engine reaches the o2 sensor because there is no mechanism to measure exhaust gas mass flow rate.

Now, I may be wrong, but this is my understanding of how it works.

Quote:
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another way to find a exhaust leak is to use a shop vacuum in reverse (blower side). place the hose in the exhaust tip, seal it up with duct tape. get a bottle of soapy water, i prefer a few drops of dawn dishwashing soap. start spraying all the flanges and watch for bubbles.
that's a pretty good idea!
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Old 03-28-10, 02:30 PM
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