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  1. #11

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    Quote Originally Posted by tbplus10 View Post
    Your truck doesnt have an after cat sensor if I remember correctly, so the only possibility is if it increases the backpressure slightly and improves low rpm torque. If it does improve you wont see much.
    Thats real low mileage, from the picture it doesnt look like you have real big tires, and Im guessing you dont haul trailets or huge loads all the time.
    Do you have a heavy right foot?
    I can sometimes. When I gordt got my license, I had a extremely light foot. Now I have a heavier foot. same mpg.
    Quote Originally Posted by Jamm3r View Post
    No, however, there's a pretty good chance that you have a leaking fuel pressure regulator which contributed to the early failure of the cat.

    You have the 5.7, right? Fixing a leaking fuel pressure regulator will improve the MPG, by a lot. They leak into the intake manifold where you can't see it, then the truck runs rich and burns up the cat.
    is the fpr a hard fix?

  2. #12

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    Hey Friends

    I got a question on the "Catalytic converter and O2 sensors". I am the second owner of my 2004 Yukon Denali and after buying it, I have been told that the exhaust system had been modified by taking out the Catalytic converter and O2 sensors. So I'm wondering what kind of impact does this have on my vehicle.

    From what I have read on the forums etc. so far I've learned that this essential component (converter and O2 sensors) help keep the gas emission cleaner but does it's absence have any other impact on vehicle performance, like fuel effeciency or any other factor? I frequently experience a slight jerk when my SUV shifts from gear1 to gear2 and rarely gear3... would this have any kind of connection with the Catalytic converter?

    I have been tracking the milage I've been getting last couple of days and it shows me 12-14 MPG in the city and 18-20MPG on the highway... I drive at about 60MPH (after learning how to be fuel efficient from fellow members input on the forums). Appreciate the stuff I keep learning from everyone.

    Awaiting a feedback. Good day.

  3. #13

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    Quote Originally Posted by atish_therock View Post
    Hey Friends

    I got a question on the "Catalytic converter and O2 sensors". I am the second owner of my 2004 Yukon Denali and after buying it, I have been told that the exhaust system had been modified by taking out the Catalytic converter and O2 sensors. So I'm wondering what kind of impact does this have on my vehicle.

    From what I have read on the forums etc. so far I've learned that this essential component (converter and O2 sensors) help keep the gas emission cleaner but does it's absence have any other impact on vehicle performance, like fuel effeciency or any other factor? I frequently experience a slight jerk when my SUV shifts from gear1 to gear2 and rarely gear3... would this have any kind of connection with the Catalytic converter?

    I have been tracking the milage I've been getting last couple of days and it shows me 12-14 MPG in the city and 18-20MPG on the highway... I drive at about 60MPH (after learning how to be fuel efficient from fellow members input on the forums). Appreciate the stuff I keep learning from everyone.

    Awaiting a feedback. Good day.
    I doubt the O2 sensors were removed, especially if you're getting that MPG you stated. The O2 sensors are a vital part of how the ECM regulates fuel and ignition timing. Reprogramming the ECM to not use O2 sensors is not an easy task; and simply cutting them out, would result in the CEL staying lit, with a very poor running truck.

    If the cat was cut out, I'd just get a new one and put it back in, if I were you. The cat plays a vital role in reducing emissions. Removing it in a modern vehicle does nothing to help performance, and can affect fuel economy (mostly in city driving), and will affect emissions.

  4. #14

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    Look at where he's posting from, emissions are optional with no real programs to verify or check in that part of the world.
    The only reason his truck had emissions from the factory was because its a U.S. mfg vehicle.
    If he's been running the truck without cats a while, as Im assuming from the post, and doesnt have a CEL, again an assumption due to no comment about CEL's in the post, I'm also gonna assume whoever did the original modifications installed either O2 simulators in the system or installed a program in the ECM to bypass or ignore certain parameters and inputs.
    All these items are available and when used will allow the truck to run normally with no issues.
    Something else is his vehicle doesnt have warranty issues like a U.S. vehicle since its almost a buyer beware situation in many countries. Only a small amount of countries require mfgrs to have or honor any type warranty, so if theres no warranty theres no reason to worry about modifications.
    What the O P needs to do is investigate a little to see if simulators or a program was used, again an assumption but whith the mileage he's getting something has been modded along with the cat removal.

  5. #15

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    Quote Originally Posted by tbplus10 View Post
    Look at where he's posting from, emissions are optional with no real programs to verify or check in that part of the world.
    The only reason his truck had emissions from the factory was because its a U.S. mfg vehicle.
    If he's been running the truck without cats a while, as Im assuming from the post, and doesnt have a CEL, again an assumption due to no comment about CEL's in the post, I'm also gonna assume whoever did the original modifications installed either O2 simulators in the system or installed a program in the ECM to bypass or ignore certain parameters and inputs.
    All these items are available and when used will allow the truck to run normally with no issues.
    Something else is his vehicle doesnt have warranty issues like a U.S. vehicle since its almost a buyer beware situation in many countries. Only a small amount of countries require mfgrs to have or honor any type warranty, so if theres no warranty theres no reason to worry about modifications.
    What the O P needs to do is investigate a little to see if simulators or a program was used, again an assumption but whith the mileage he's getting something has been modded along with the cat removal.
    Yes, I saw the location. Emissions laws are irrelevant. The law existing there or not, doesn't change how a vehicle is built to function.

    As for a "simulator" device for an O2 sensor, it's pointless and makes absolutely no sense. Plus, it would be lying to the ECM about the oxygen content in the exhaust, and could very well cause problems. The only easy way I know of to bypass the use of O2 sensors in the ECM, would force it to operate in open loop mode at all times, and would reduce fuel economy, as well as the amount of power being made by the engine.

    And he's not the OP. But yes, he obviously needs to look underneath the truck for obvious modifications, and to verify what was done. He also didn't ask what was done, but rather what effects it could have on the engine. There's no need to make assumptions about what may or may not have been done.

  6. #16

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    The only easy way you know of yes, but theres more than one computer programmer that knows how to make an ECM run an engine problem free with very few program changes.
    In this case a simulator wouldnt be pointless if you programmed the ecm to do only what you wanted it to do.
    All the sensors are doing is telling the ecm what they see so it can change the fuel rates according to its parameters so it doesnt run to lean or to rich. At sea level which is where this vehicle is operated parameters wont change much at all. Theres no worry of a rich fuel mixture overloading the cat since it doesnt exist.
    I have "home made" operating systems for 2 of my trucks that are only used off-road, they were both custom designed by a friend that took less than an hour to tailor them from factory to custom including using water and alcohol injection on one of them. Both trucks have passed local emissions. So I know for a fact simulators arent "pointless" the engine can run without being in open loop and can still return decent mileage and power. Its all in what the ecm tells the various components to do. Besides just how did engines operate before modern electronic systems? Everybody seems to forget a combination of old and new systems can be incorporated on a vehicle and they still run correctly. Especially in a country where noone checks emissions and engine operating systems. Most of the changes made to vehicles modified in the U.S. concentrate on keeping the system from tatteling on you, when you dont have to worry about that its a lot easier to mod the system.

  7. #17

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    @dobey and @tbplus10... I really appreciate the input from both of ya'll!

    Emm yeah, I'm sorry I forgot to mention about the CEL being on constantly, my appologies. The law is not very strict about the cat converter but I would prefer being more envoirnment friendly, just personal preference. I have no idea about simulator's so wouldn't know, morever since I'm not into modifying for performance, I'm pretty new at this stuff... Like I said I keep learning more and more through the awesome forums.

  8. #18

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    Quote Originally Posted by atish_therock View Post
    @dobey and @tbplus10... I really appreciate the input from both of ya'll!

    Emm yeah, I'm sorry I forgot to mention about the CEL being on constantly, my appologies. The law is not very strict about the cat converter but I would prefer being more envoirnment friendly, just personal preference. I have no idea about simulator's so wouldn't know, morever since I'm not into modifying for performance, I'm pretty new at this stuff... Like I said I keep learning more and more through the awesome forums.
    Get new cats and put them back in where they belong, and replace any missing O2 sensors. Scan the ECM for codes (the CEL could potentially be something else), as well. Most likely if the cats were removed, the post-cat O2 sensors were simply removed as well, given they are likely installed in the tube immediately after the cat, and the replacement "test pipes" did not have O2 sensor bungs welded onto them.

    - - - Updated - - -

    Quote Originally Posted by tbplus10 View Post
    The only easy way you know of yes, but theres more than one computer programmer that knows how to make an ECM run an engine problem free with very few program changes.
    In this case a simulator wouldnt be pointless if you programmed the ecm to do only what you wanted it to do.
    All the sensors are doing is telling the ecm what they see so it can change the fuel rates according to its parameters so it doesnt run to lean or to rich. At sea level which is where this vehicle is operated parameters wont change much at all. Theres no worry of a rich fuel mixture overloading the cat since it doesnt exist.
    I have "home made" operating systems for 2 of my trucks that are only used off-road, they were both custom designed by a friend that took less than an hour to tailor them from factory to custom including using water and alcohol injection on one of them. Both trucks have passed local emissions. So I know for a fact simulators arent "pointless" the engine can run without being in open loop and can still return decent mileage and power. Its all in what the ecm tells the various components to do. Besides just how did engines operate before modern electronic systems? Everybody seems to forget a combination of old and new systems can be incorporated on a vehicle and they still run correctly. Especially in a country where noone checks emissions and engine operating systems. Most of the changes made to vehicles modified in the U.S. concentrate on keeping the system from tatteling on you, when you dont have to worry about that its a lot easier to mod the system.
    Sea level operation is irrelevant. The O2 sensors have nothing to do with content of intake air. They tell the ECM how much oxygen remains in the exhaust after combustion, and then again after being catalyzed in the converter, so that it may adjust fuel and ignition parameters to compensate for other factors, such as reduced efficiency over time, inefficient mixtures of fuel in the tank, etc…

    I don't know what you mean exactly by "home made operating systems" but there is no way an entire operating system was written in less than an hour. Changing fuel and timing tables, sure. But that is a far cry from an operating system. I also don't know anything about those 2 trucks, such as what year they are, what ECMs are being used, etc… I didn't say it wasn't possible, I said it wasn't easy or simple. Sure there are plenty of things one can do. But the best thing one can do, is not make assumptions about what other people are doing, particularly in such unstable areas of the world, to their trucks, because of what you or your friends did to your own trucks.

  9. #19
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    I just leave the pos out and use a dummy o2 sensor...
    Chuckie!!!


  10. #20

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    Quote Originally Posted by BurbanMan View Post
    I just leave the pos out and use a dummy o2 sensor...
    Not at all useful or helpful to answering the question asked. It's not a pos, it's a very useful piece of equipment, and removing it does nothing at all to help the engine.

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