Could a freer flowing exhaust cause the engine to run a little leaner...
03-20-2002, 07:45 AM
#1
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Could a freer flowing exhaust cause the engine to run a little leaner...
...if the ECU programming is not specifically adapted to the freer flowing exhaust? (i.e., stock exhaust vs. cat back alone, or vs. downpipes+cat back, etc.)
03-20-2002, 08:00 AM
#4
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Wont the MAF take car of that?
As long as it can measure the amount of air going in, and the temp at the intake, shouldn't it be fine? Freer flowing exhaust will mean more air coming in, right?
03-20-2002, 08:05 AM
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Software should adjust fuel based on MAF readings -- so it should not run lean at all...
and if it does start to lean out, he O2 sensors will see, and make the ECU dump more fuel 
If it's too much out-of-spec (ie, always on the 'lean' side) you'll throw a DTC.
-T
If it's too much out-of-spec (ie, always on the 'lean' side) you'll throw a DTC.
-T
03-20-2002, 08:11 AM
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Mass air meter should compensate for the increased airflow
An exhaust alone should not be enough to throw off a mass air system. Trubos, downpipes, and an exhaust could require a programming change. It depends on how much variance the system can handle.
03-20-2002, 08:36 AM
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Nah...you'd get a long term fuel trim DTC if it was even significant.
That's the wonder and beauty of the ECU....it basically tunes the car on the fly based on it's sensor input. You can change a lot of stuff and it adapts (within reason).
RR
RR
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03-20-2002, 07:45 PM
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O2 sensors don't do squat at wot...
Car runs off ecu maps for maf input at wot, which is when running lean is oh so bad.
The only things that will save the engine at wot in the S4 are the egt and knock sensors. If you run standalone you can do some serious damage mighty fast bypassing those.
The only things that will save the engine at wot in the S4 are the egt and knock sensors. If you run standalone you can do some serious damage mighty fast bypassing those.
03-20-2002, 08:50 PM
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Umm NO
Once again we disagree completely. Unless you are claiming that S4 O2 sensors are wide band you can not be correct (and anyone trying to run racegas knows they are NOT wideband). Look up how O2 sensors work on any technical website.
My synopsis:
Oxygen sensors work by oscillating between rich and lean to achieve a perfect air/fuel mixture (.45 volts usually). It does this in something called "closed loop" operation, where the ecu uses the O2 sensor signal to modify the amount of fuel injected. Once you go to WOT, the O2 sensor becomes useless as the engine needs to run richer than in closed loop operation, and therefore the car disregards the O2 sensor and enters "open loop" operation until you get off the gas pedal. At this point the ecu reads the maf signal and injects a set amount of fuel into the engine REGARDLESS OF O2 SENSOR VALUES!
The S4 is a regular lambda type O2 sensor that utilizes open loop operation. There is no way the O2 sensors will be of any help at wot. And the self study manual says exactly that.
It SAYS "engine operation with lambda = 1 is possible !!!UP TO!!! high load and engine speed ranges. Don't misunderstand that sentence to mean AT high load and engine speed ranges.
My synopsis:
Oxygen sensors work by oscillating between rich and lean to achieve a perfect air/fuel mixture (.45 volts usually). It does this in something called "closed loop" operation, where the ecu uses the O2 sensor signal to modify the amount of fuel injected. Once you go to WOT, the O2 sensor becomes useless as the engine needs to run richer than in closed loop operation, and therefore the car disregards the O2 sensor and enters "open loop" operation until you get off the gas pedal. At this point the ecu reads the maf signal and injects a set amount of fuel into the engine REGARDLESS OF O2 SENSOR VALUES!
The S4 is a regular lambda type O2 sensor that utilizes open loop operation. There is no way the O2 sensors will be of any help at wot. And the self study manual says exactly that.
It SAYS "engine operation with lambda = 1 is possible !!!UP TO!!! high load and engine speed ranges. Don't misunderstand that sentence to mean AT high load and engine speed ranges.