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WONT PASS SMOG!! running too rich!

Discussion in 'Performance & Fuel' started by norcalbear05, Apr 30, 2009.

  1. norcalbear05

    norcalbear05 Rockstar

    went to take my biannual smog test to renew the registration today and failed, ran too rich and cant figure out why?


    ran it to get more than warm enough before showing up for the test, havnt made any changes to the fuel system. still dont know whats wrong. if anyone has tips or checks id gretaly appreciate it before spending the over priced fee of getting the diagnostic.



    the test results:
    Hydrocarbons max @ 15 mph is 118 ppm/ MINE was 172 FAIL
    Hydrocarbons max @ 25 mph is 98 ppm/ MINE was 156 FAIL

    CO max @ 15 mph is 0.68%/ MINE was 1.07% FAIL
    CO max @ 25 mph is 0.87% / MINE was 0.56% PASS

    thanks!!
  2. GaryL

    GaryL Epic Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    My 89 Suburban didn't pass a couple of years ago and it seemed to run fine. We replaced the EGR, no change. Did a full tune-up, no change. Replaced the Cat, passed with flying colors.
  3. norcalbear05

    norcalbear05 Rockstar

    yea i was thinking it might be the cat, although i did put the cat thats on it in new about 6 years ago, i wouldnt think it would go bad that fast.

    i did recentlly change out my spark plugs before taking the test because it was lagging in take off power and found one of them (or maybe more) had been burnt up and wasnt combusting (dead cylinder).

    do you think because of those cylinders not firing over time could have jacked up the cat converter because of all that air and fuel mixture going through unburnt?

    i just dont want to waste the money on a diagnost. if i can figure it out myself. lol
  4. Blazerado

    Blazerado Rockstar 100 Posts

    Use a scanner and check your O2 sensors. If they dont come out of closed loop it can cause the same issue.
  5. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Your cat is probably shot. Running raw fuel through it will kill it prematurely. A bad O2 sensor will set an O2 code.
  6. norcalbear05

    norcalbear05 Rockstar

    thats what i figured.

    takeing it in for diag. scan on mon, let yall know the results.

    thanks for the help as always!!
  7. MrShorty

    MrShorty Epic Member Staff Member 5+ Years 1000 Posts

    Diagnose it properly. Running rich will kill cats, but replacing the cat doesn't fix the running rich problem, which means the new cat will have a short life.

    I'm not familiar with diagnostics on the TBI motors. Back when I had an '88, you could pull trouble codes by simply jumpering two terminals on the ALDL -- I fully expect your '90 has the same functionality: http://www.troublecodes.net/GM/ If the SES/CEL has come on, I'd probably start by pulling codes (as easy as it is, I might pull codes even if it hasn't been on). The primary function of the engine management (aka OBD1 system) is to control fuel mixture.

    I don't know how to check fuel pressure on the TBI motors, but high fuel pressure can cause a rich condition. Check for leaks into the throttle body/intake (such as a leaky injector) which can cause a rich condition.
  8. bd1326

    bd1326 Rockstar

    you ever thought of moving out of cali? no more failed smog test
  9. norcalbear05

    norcalbear05 Rockstar


    i was told before to try this to see what codes come up but i figure i might as well go through with the full diagnostic, luckily a buddy has a shop and is taking care of it for me otherwise id be out about $100 to run it. if it wasnt for that id be doing the paper clip method for sure, lol.

    and i wish i could move out of cali for all the troubles here and stupid laws, unfortunately the pleasures outweigh the pains.

    :glasses:
  10. novaman64

    novaman64 Member

    Denatured alcohol. Look i tup online, if you just wanna squeek by it might help you out.

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