Car failing smog, nox way high

  • #1

    Car failing smog, nox way high

    Took the z in for the always awesome cali smog check and failed the nox test misserably. Whenever ive tested it in the past its passed just barely.

    This time my o2 and hc were well below the max but the nox tested at 1200 with a limit of 700.

    Im thinking its the cat but wanted to check what you guys thought first. I checked the egr, tries to stall when pushed up and diaphram moves when engine reved. I sea foamed the car yesterday if that could effect it.

    Thanks for any help
  • #2
    It tested 1200 nox at 15 mph btw. The shop didnt even take it higher when they saw that
  • #3
    I had the same issue and made the same observations as you. What I found was that when I drove the car, same as on the dyno, the vacuum signal to the EGR was only a few inches of vacuum. Verified at the source to the solenoid and after to the valve. 3-5 inches vacuum is not enough to open the valve far enough to be effective, but the valve jumps a little when you rev the engine, making you think its OK. I was a little embarrassed to have fallen into this trap after finding it. I should know better. I started space shuttling about what the cause could have been before I made a simple test and found that.
    The NOx shouldn't be that high without a cat if the EGR was working. Try switching the vacuum source to the "other" port on the throttle body. That had manifold vacuum level. Car flew through smog after that. Like 50ppm NOx. Note that the car will surge a little at part throttle after using the other vac port so I haven't sorted that out yet.

    My car had barely passed the previous two smog checks also. Embarrassingly even put a cat on it to make it pass one year. The vacuum source had been that way all along. Switch it back after the smog test if he surging is an issue.
  • #4
    Thanks for the help. I did what you suggested and bypassed the egr solenoid and hooked the egr directly to the manifold. It made it idle like shit but she passed!

    The smog tech couldnt beleive it passed after seeing the nox readings from yesterday and after seeing how much worse it ran today (due to the egr bypass) hahaha

    Thanks again!
  • #5
    HAHA

    RIGGED TO SHIT

    PASSED THO

    LOL

    SWEET

    fuck california
  • #6
    It's rather ironic that for people who understand emissions results, it actually tells you a lot of things about your setup, yet no one seems to use it as a diagnostic tool for that