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All About Exhaust Systems



  • Cats can take a certain amount of excessive fuel-burning--what it can't take is RAW fuel. Cats can ever tolerate lots of oil burning.

    I'm quite puzzled by this problem. I would have suspected a bad ECM module except he passed the smog test.

    Very often these types of difficult problems lack a critical detail that has not been reported (or perhaps observed) by mechanic or owner, and once that detail is known, we all slap our foreheads and say OF COURSE! :P
  • srs_49srs_49 Posts: 1,394
    Me too, puzzled that is.

    I mean, if the engine was really running that rich, and the front O2 sensor was working correctly, wouldn't the ECU try to lean things out to try and keep the air/fuel ratio at the stochiometric point (what's that 14:1?)? Then if it couldn't do that, throw a code?
  • mg45mg45 Posts: 8
    How do they do the smog test? The car was inspected before i drove it off the lot on April 6th 2009 and it apparently passed. Unless the dealer forced the pass, because after all they did sell it to me with a bad tranny. I'm getting it inspected at the end of march and I'm thinking it will pass if they just do the inspection by scanning for codes, which i don't have. I am really hoping it fails, then they have to find out and tell me whats wrong with it.
  • obyoneobyone Posts: 8,065
    I am really hoping it fails, then they have to find out and tell me whats wrong with it.

    You should get an "A" for creativity as I've never heard of that one before... ;)
  • mg45mg45 Posts: 8
    My 2007 camry failed when i brought it to the dealer for inspection and they called me saying what needed to be done to get it to pass. it cost 200 bucks, something with emissions, but it then passed. I don't know if the same goes for the saturn, but i did buy it from that same dealer.

    I just was looking under the hood, searching for any fuel and or vacuum leaks when i noticed this weird noise coming from the manifold when i rev it. Heres the video:
  • kiawahkiawah Posts: 3,666
    Personally, I don't like that sound, or the whining. That would bug me until I either concluded it wasn't a problem, or found what the problem was.

    Try popping the accessory belt off, and then start the vehicle and run it briefly to see if the whining stops (then proving it's external to the engine), or continues to whine. I don't know the saturn specifically, but look on the tensioner pulley assembly for either a wrench or pry bar attachment point. Take the tension off the belt, slide the belt off, then slowly release the tensioner to it's rest position. Take note of how the belt routes, so you can put it back the same way.

    If the whining stops with the belt off, turn the engine off, and with your hand slowly turn/wiggle each accessory to see if you can feel which bearing is a problem.
  • mg45mg45 Posts: 8
    Ok, i figured out the noise was coming from the pcv valve. It just the little ball in the valve bouncing around. As for the gas mileage issue i think i made have cracked the code.

    As I listed I recently replaced the fuel filter. I bought one from auto zone for 35 bucks. The fuel regulator for the 98-02 s- series is located in the fuel filter. The 35 buck one is JUST the filter, no regulator. Basically the cars running with no fuel regulator. The previous owner must have done the same thing and put in a filter with no regulator, which is why I've been getting the bad gas mileage since i bought the car. That would also explain the black soot on the exhaust pipe.

    I have no idea how the car is running practically perfect with no regulator, but the map sensor must be making up for it enough not to throw a code. I'm gonna order the OEM 92 dollar regulator/filter from and see what happens.
  • tjh1990tjh1990 Posts: 4
    hi can u help please i want to buy a after market back box not expensive 1 but i just wondered how to fit and how easy is it?
  • tjh1990tjh1990 Posts: 4
    hi i am wanting to buy a after market back box how and how easy is it to fit?
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,693
    How difficult it is depends a lot on the type of car and type of system. Usually the vendor can give you some idea of labor involved. Often the hardest part is getting under the car if you don't have a lift. Then there's the problem of whether your present exhaust system is all rusted up or not. Sometimes a muffler shop will install it for you for not too much money. If you're just buying the back muffler and not pipes, this is usually pretty easy to fit.
  • tjh1990tjh1990 Posts: 4
    thats what i want how do i fit the muffler
  • tjh1990tjh1990 Posts: 4
    i want to fit a muffler how do i do this and what difference will it make
  • obyoneobyone Posts: 8,065
    A low restriction muffler will give you a higher maximum rev point usually accompanied by a louder sounding exhaust at the expense of loss of low end torque. Depending on what vehicle you're talking about you could have one installed for under $100.
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,693
    It'll just make more noise basically. There's no power inside a muffler itself. If you put on an entire cat-back system, maybe, depending on the car, you'd get a few more HP. Is it worth the money?? Probably not, unless you like the louder exhaust note.

    But anyway, fitting just a rear muffler to most modern cars is usually just a matter of undoing some clamps and hangers. But you'd best check to see that yours isn't welded up, especially if it's an older car. Muffler shops often weld in replacement mufflers.
  • obyoneobyone Posts: 8,065
    Actually if you want to remove restriction, knocking the honeycomb out of the cat works better than any low restriction muffler. Course you'd have to get dummy o2 sensors and live in a nonemissions state.
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,693
    You'd probably get the most horsepower from no mufflers at all, presuming back pressure was sufficient in the exhaust header tubes. But that would be quite noisy :P

    Getting any real HP boost is generally expensive.
  • is this illegal though?
  • obyoneobyone Posts: 8,065
    edited June 2010
    is this illegal though?

    Yes it is. Does that stop someone who can't afford a new cat or looking to cheaply increase performance? Nope not in a state that doesn't have emissions testing.
  • New poster here with more of a statement than a question and looking for feedback.....
    I run a fleet of 127 GMC and Chevy 3500 cutaway box trucks. The 2 issues that have cropped up consistently over the past few years are fuel pumps (inadequate design) and exhaust manifolds that crack before 100,000 miles. I researched every manifold repair I had done and noticed a pattern of prior O2 sensor failure of some sort in nearly every instance. Out of the 9 documented cases, 4 of the trucks also had to have new catalytic converters. My theory is this: Faulty O2 sensors or deteriorating cat converters are the culprits. I believe it's a domino effect starting with the sensor which in turn destroyed my converters and subsequently cracked the manifolds.

  • srs_49srs_49 Posts: 1,394
    IMO, I do not think a bad cat would damage an exhaust manifold.

    One way to kill a cat is to have a overly rich fuel mixture , or misfire, which leads to high amounts of unburnt fuel in the exhaust, which in turn "burns" in the cat, overheating and destroying it.

    So, maybe the crack in the manifold occurred first. This may have led the O2 sensor to think the engine was running too lean, so it caused the ECU to richen then air-fuel ratio, which results in high amounts of unburnt fuel in the exhaust stream.

    Just a theory.
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