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Another smog question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blazinaire, Jun 20, 2002.

  1. Blazinaire

    Blazinaire 1/2 ton status

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    Well I finally managed to get the idle speed down within acceptable limits. BUT, now the hydrocarbons (?) are too high at idle. I didn't have it tested at a smog shop, just a local garage, so the guy wasn't too sure how to fix it. He said that my catalytic converter was to blame, does that sound logical? I found the stock cat for about $160, and a "high flow" cat for only $90. I have 1 week to pass and don't want to spend money on parts that I don't need. Anybody now anything about how to lower the hydrocarbons (?) on my '87 TBI 350?
     
  2. chris672

    chris672 1/2 ton status

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    I was told by a smog tech that changing your oil can lower HC's. Did the garage test your cat? If it is bad then a new one will help.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    Post/reply from the monte list

    ">With that said, HC is HydroCarbons. In effect, unburned fuel. The higher
    >this is, the less complete the car's combustion is. One real good way to
    >send this sky-high is to have a cylinder that's not firing. That will blow
    >raw hydrocarbons into the exhaust. It can also be a result of running too
    >rich....dumping too much fuel into the mixture.

    Yep. If your motor is firing properly, it shouldn't have high HC's, unless
    it's also rich (not enough air to combine with the HC's to make CO2's and
    H2O's).


    >CO is Carbon Monoxide, another result of incomplete combustion. It seems
    >to follow the "richness" of the mixture...that is, the richer the mixture,
    >the higher the CO readings.

    Yep, not enought O2 to complete the CO2 conversion, so it stops at CO....
    Mine did this: was running rich.


    >NOx are Oxides of Nitrogen. It's been explained to me (and I have yet to
    >prove it) that this is the reading that's the most affected by the
    >catalytic converter. I know the other readings are affected by the cat,
    >but I've heard people swear that high NOx readings indicate a bad cat.

    The opposite is true: Cats work to remove like 80% of bad HC and CO readings
    but only affect NOx by maybe 50%.

    I had a great post on what AZ lists as possible culprits for high emissions.
    See Feb. 2001 posts by me.... (I'd send it to you, but don't have access
    to my saved email, being away from home).

    NOx is created due to heat. More compression, hotter motors, more timing
    advance, and leaner mixtures, contribute to high NOx. More octane, lower
    T thermostat, and more fuel all reduce NOx.

    Conversely, the opposite is true for HC and CO: leaner mixtures result in
    lower readings, (until the mixtures are so lean, they misfire....)

    So, for places that test all three emissions, you have to stay right around
    the ideal range: no going too rich or lean or hot or cold."

    As well, denatured alcohol in the gas is a good thing for emissions testing : )
     
  4. creampuff90k5

    creampuff90k5 1/2 ton status

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    Forget all of that catalytic converter bullsh!t. All you need to do is make sure the engine has fresh oil and spark plugs, then right before you get to the inspection place, pull over and remove the air filter. Run it through inspection with no filter - this works every time. Don't forget to put it back in when you're done!
     
  5. rampage

    rampage 1/2 ton status

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    How did you finally get your idle down? It was up at 1400 wasn't it?
     
  6. Blazinaire

    Blazinaire 1/2 ton status

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    dyeager535: Thanks for that info, it really cleared things up for me /forums/images/icons/laugh.gif , and come to think of it my truck does have the occasional missfire. I did end up ordering a "high-flow" cat being that I sank my truck in salt water (couldn't be good for it /forums/images/icons/tongue.gif ) since last smog and it is the original cat with over 180k on it. Hope that this will clean it up enough! creampuff90k5: My oil was just changed, and the spark plugs are new too. While we were tinkering with my truck for the pretest (hooked up to smog machine) the air cleaner was off; still failed /forums/images/icons/shocked.gif . rampage: I really can't explain how I finally got the idle to stay down. I just unplugged the harness from the IAC, removed the IAC and adjusted it, and when I reassembled it the computer decided to cooperate /forums/images/icons/crazy.gif ! Hey, as long as it's working, why question it /forums/images/icons/grin.gif ?
     

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