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Didn't pass emissions

Discussion in 'General Chevy & GM Tech Questions' started by jprimrose4292, Jan 2, 2009.

  1. jprimrose4292

    jprimrose4292 Member

    have a 93 c1500 with a 350. I just bought it and took it to get the emissions checked and it failed at idle.

    This is the info that they gave me.
    (reading/Limit)

    Cruise HC:104/200
    CO2:0.6/1.5
    CO+CO2: 15.1/6
    O2: 0.96/NA
    Passed

    Idle HC: 342/220
    CO: 4.47/1.2
    CO+CO2: 16.27/6
    O2: 0.75/NA
    RPM: 680

    Failed

    Any information or suggestions at to what is wrong would be appreciated. I know that it was sitting for some time so I have been taking it on the freeway and tring to get it really warm. I will be doing a full tune up on it also.

    Thanks
  2. ChevyFan

    ChevyFan Administrator Staff Member 5+ Years 5000 Posts

    More info please.

    - How long have you owned it? How many miles have you driven?
    - Have you cycled through all of the gas that was in the tank?
    - How many miles are on it? How long was it sitting?
  3. jprimrose4292

    jprimrose4292 Member

    I have had the suburban for about a week (it had been sitting for about 6 months) and have gone throught the tank that was in it. I filled it with a mid grade unleaded in hopes that it would help some. I have driven about 300 miles in it so far. It currently has a little over 172,000 miles on it.
    Last edited: Jan 2, 2009
  4. unplugged

    unplugged Epic Member 5+ Years 1000 Posts

    I would guess 75k+ miles on the truck. High CO at idle with little improvement at cruise speeds points to a bad cat. About $150 for the cat installed. If you don't have a 3" catback system you might want to go ahead and add it. Did my 93 burb recently for $340 for both. See my earlier post on getting my beast smogged at: GMTC
  5. JMoney02

    JMoney02 Epic Member 5+ Years 500 Posts

    You have High Hydro Carbons (HC), which can be the cat, o2 or the egr valve. Run a can of Seafoam through the system, don't do a major tune up before(good mechanic) will tell you this as it is not going to provide any results, you need to correct the emissions first and these are the three major players. Did they do the tailpipe test for the O2 reading? Chage the fuel filter, PCV valve and then Seafoam, drive with a tank full and then test again.......


    Jeff
  6. PencilPro

    PencilPro Member


    What is Seafoam?
  7. gassy

    gassy New Member

    How does the truck idle now ? How aboiut before it as parked ? Any sign of misfire ? When was the oil changed last ? I also do not see a NOX result ? blah blah blah :lol:



    Any rough idle can be a cause of misfire from bad wires, plugs, coil, cap etc. A misfire can increase emissions by up to 75% each time a cylinder misfires. During higher RPM operation the increased air helps to eliviate the condition. A dirty air filter can hinder emissions. A stuck EGR can cause rough idle as well, it is designed to lower combustion temperature, but not at idle. There is a vacuum line on the EGR valve, unplugging it at idle should render no result normally. The next test is to place some vacuum on the EGR valve by sucking into a vacuum hose attached to the EGR valve port. A properly working EGR valve will casue the engine to stumble or stall ( at idle ) when you draw vacuum on this port. No result can mean a stuck EGR valve or clogged feed tube from the manifold ( a clogged feed tube will not affect idle emissions, only cruise ). A partially stuck open EGR valve can cause idle emissions problems.

    Always perform the emissions test with a fully warmed up engine, especially during winter months ! Actually a good 15 - 20 mile highway run beforehand is good to get things good and warm, also do not shut off the engine in the lineup. All this will ensure your CAT has lit properly and the O2 sensor(s) are clean, hot and reading correctly ( especially after sitting ).

    High HC and Co can be due to an overrich condition. One culprit is your oil, over time oil retains fuel that gets washed down the cylinder walls ( one reason oil gets dark), then the vapour is released back through the PCV system, it is always a good idea to do a fresh oil change prior to an emissions test.

    A result for NOX ( oxides of nitrogen ) reveals the combustion temperature ( rich or lean ) and if the cat is working properly under these conditions.

    Do what you can to tune the truck up, but an oil change and a good hiway run may be the answer. Remember, good and warm before the test.
  8. jprimrose4292

    jprimrose4292 Member

    Well I went out and bought a can of seafoam (from what i read that some pretty good "S") But I figured that I would do the tune up and change the oil. Im not sure how it ran before(just bought it) but even now it runs really well. Was actually suprised that it didnt pass but had a feeling because it sat for so long it wouldnt.
  9. vncj96

    vncj96 Epic Member 5+ Years 1000 Posts

    If it doesnt require the higher octane dont use it, it was never designed to be used, you may not be burning it all up as it requires higher ignition point and that old of a truck doesnt have a computer to adjust that like new cars do
  10. jprimrose4292

    jprimrose4292 Member

    Well over the weekend seems as the alternator decided to go also. Noticed that the speedometer wanted to go 80 in park. lol. But the new alternator seemed to fix that also. Hope fully now ill get to the rest of the tune up. I bought a can of seafoam also so ill keep you guys updated. Thanks again.

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