Exhaust leak... why do you lose power?
08-09-2010, 09:41 AM
#2
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Depends on where the leak is. The closer the leak is to the head, the more it will affect the car. Also, if your leak is in front of an O2 sensor, then the sensor will read too much unburnt oxygen in the system which, in turn, will cause the car to run richer in order to compensate. So, fuel gets dumped into the system, but never takes care of the extra air being read by the sensor, so it richens up more and so on and so forth. A car running pig rich is not the best state of tune.
08-09-2010, 02:12 PM
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'03 E55
I was somewhat curious about this as well, as my primary cat housing recently split all the way around (had no idea they get $2,300 for a new cat
).
The part of the explanation that doesn't make sense to me is how the O2 sensor would read too much oxygen, as the system should be under positive pressure, which should prevent the intake of any outside air through the leak (at least that is how I'm reading it). Any further explanation would be appreciated.
).The part of the explanation that doesn't make sense to me is how the O2 sensor would read too much oxygen, as the system should be under positive pressure, which should prevent the intake of any outside air through the leak (at least that is how I'm reading it). Any further explanation would be appreciated.
08-09-2010, 02:15 PM
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Viper GTS
08-09-2010, 02:20 PM
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The other thing I was thinking of was open vs closed loop ... Are the o2 sensors active at WOT , surely this would be read off the maps...?
08-09-2010, 02:30 PM
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E55 AMG
Exhaust is not coming out of an engine like water out of a garden hose, rather each individual exhaust pulse is like a smoke ring blowing into your exhaust system. When one of these smoke rings blows past your exhaust leak you hear the high pressure wave going past, then as it passes there is a low pressure point immediately behind which will in turn draw atmosphere (air) into the exhaust system through the point of leakage , therefore leaning out the mixture in the exhaust system. Does that make more sense now?
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08-09-2010, 02:34 PM
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'03 E55
The funny thing about the accident was, that out of over $8,000 in damage, nearly $5,000 was for factory exhaust parts.
08-09-2010, 02:35 PM
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'03 E55
Exhaust is not coming out of an engine like water out of a garden hose, rather each individual exhaust pulse is like a smoke ring blowing into your exhaust system. When one of these smoke rings blows past your exhaust leak you hear the high pressure wave going past, then as it passes there is a low pressure point immediately behind which will in turn draw atmosphere (air) into the exhaust system through the point of leakage , therefore leaning out the mixture in the exhaust system. Does that make more sense now?
Thanks, that makes complete sense.
08-10-2010, 08:00 AM
#10
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Exhaust is not coming out of an engine like water out of a garden hose, rather each individual exhaust pulse is like a smoke ring blowing into your exhaust system. When one of these smoke rings blows past your exhaust leak you hear the high pressure wave going past, then as it passes there is a low pressure point immediately behind which will in turn draw atmosphere (air) into the exhaust system through the point of leakage , therefore leaning out the mixture in the exhaust system. Does that make more sense now?
08-10-2010, 10:37 AM
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08-11-2010, 02:34 AM
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E55 AMG
Yeah, the condition will exist as long as the exhaust leak is there, During closed loop the computer is gathering information from sensors and making optimization calculations, when you mash the go pedal you revert to open loop and are basically operating on preset parameters where 14.7 to 1 in not the ideal AFR and a much richer mixture is required.
08-11-2010, 08:47 AM
#13
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if you have a big enough leak you will lose back pressure and gas velocity,hence lose low end power.
if you have a leak before the 02s you will lose exh there and the 02s wont read it and add fuel because it thinks the car is running leaner than it is.
Redline,we have a huge 5.5 v8 with a blower slamming boost down its throat,I cant see how air could ever get sucked in at the headers or anywhere in the system with all that flow coming out.
its not running lean because fresh air is hitting the o2s,its running lean because unmetered air is flying out the leak!
if you have a leak before the 02s you will lose exh there and the 02s wont read it and add fuel because it thinks the car is running leaner than it is.
Redline,we have a huge 5.5 v8 with a blower slamming boost down its throat,I cant see how air could ever get sucked in at the headers or anywhere in the system with all that flow coming out.
its not running lean because fresh air is hitting the o2s,its running lean because unmetered air is flying out the leak!
Last edited by skratch77; 08-11-2010 at 09:00 AM.
08-12-2010, 12:19 AM
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E55 AMG
well, actually skratch you are thinking in fast motion. if you think about the way things are happening in s l o w m O t i o n you will realize that even at redline and max boost the same combustion events are taking place, the same valves are popping open and closed and although the events are taking place very rapidly, the same "smoke rings" are passing albeit at a rapid rate. Conversely the same is happening on the fuel side of things. At redline each fuel injector is not just dumping fuel. Even at maximum duty they are spraying a fine mist of fuel for a specific number of milliseconds and are working in perfect synchronization with all the other components of our complex engines. Actually i find that thinking about complex things in slow motion can help give a unique viewpoint that can help one understand things that once seemed to just happen as a blur.
