Air flow problem

Discussion in 'General Chevy & GM Tech Questions' started by Charity, May 31, 2013.

  1. Charity

    Charity New Member

    I have a 98 tahoe I'm havin an air flow problem with it, I cleaned out all the honeycomb in the cats and it now makes an empty rattling noise, my truck tries to die while driving, and my engine light is still on. I want to put straight pipes in it but not sure how my o2 sensors are going to react and I do not have a tool to change the temp on the cot....any suggestions?
  2. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    What codes are coming up?
  3. Charity

    Charity New Member

    The guy didn't tell me but he said my cats were clogged....
  4. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    Do you trust his diagnosis?

    I personally am not fond of people simply removing the cats. It is technically illegal (though in communities where they don't do emissions testing, it is unlikely you would get caught.

    Did gutting the cats change the symptoms at all? If not, I would suspect that something else is going on. Where the engine light comes on, diagnosis almost needs to start with the code(s) the PCM is throwing. Having gutted the cats, there will probably also be post-cat O2 sensor codes (P0420 and/or P0430).

    Clogged cats/exhaust (especially to the point of stalling the engine) can usually be checked with a vacuum gauge. The engine will show little to no vacuum, where normal vacuum is 18-20 in Hg.

    Another thing I would probably check, especially if there is little reason to trust the clogged cat diagnosis, is fuel pressure. These engines are really stubborn if the fuel pressure is too low (as low as 50-55 psi will cause rough running).
  5. j cat

    j cat Epic Member 5+ Years 1000 Posts

    what happens is the cat converter with the failure of fuel injection / fuel management the cat converters over heat and break up/melt. then the damaged internal metal material gets to the muffler and plugs up that. with no cat converter you will always get DTC errors.

    I would get a cheap exhaust system to replace whats there now. installing new converters as well.

    when the converters are hollowed out you will get the rattle noises.

    now I am assuming that the shop knows what there doing and did properly check for restricted exhaust.

    as was mentioned your problem could be a fuel delivery issue. check the fuel pressures with a pressure gauge . with the 5.7L you need 55-65 PSI ..55 psi with the engine running.
  6. Charity

    Charity New Member

    Air flow

    I will definitely check the fuel pressure, does this check the pump? I am buying a whole new exhaust system to put in along with new o2 sensors....

    - - - Updated - - -

    I don't trust the diagnostic system or the shops proper check, I will be installing this myself. I do smell fuel burning now as I drive my truck.
  7. Charity

    Charity New Member

    Now that I have replaced the cats and the o2 sensors, my cylinder #5 is flooding with gas and hydrolocking my engine...everytime we release the gas and try to start it, it fills again. Throttle body has been replaced in the past couple years...

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