EGR cleaning - high NOx during emissions test

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Cadillac Tech Tips - How to fix it Discussion, EGR cleaning - high NOx during emissions test in Item Specific Cadillac Discussion; I thought I would share my experience since I didn't find enough details when I searched for info: My mother's ...
  1. #1
    mkoz is offline Cadillac Owners Member
    Automobile(s): '92 Eldorado
    Join Date
    Apr 2009

    EGR cleaning - high NOx during emissions test

    I thought I would share my experience since I didn't find enough details when I searched for info:

    My mother's '92 Eldo (PFI) failed its emissions test back in November. It was more than double the limit on NOx. CO and HC barely registered. Classic symptoms of an EGR problem. Car has 113K km (around 65K miles).

    The EGR valve had been previously replaced prior to the November emissions test due to a code being displayed, but it still failed with a new valve. Car was parked till now. I ran some TB cleaner through it, burned through a tank of injector cleaner and went in for a retest yesterday. Failed NOx by more than 4x the limit (warmer weather). So last night I removed the throttle body, cleaned off all the carbon on it, then I went to town on the EGR system. The two tubes in the middle of the intake plenum were gummed up with carbon, I'd say 50% clogged. I snaked them with a mini drain snake from the dollar store, did the same thing on the EGR valve ports (left is exhaust source, right is intake which comes up those two tubes in the middle of the intake plenum). Finished everything with some TB cleaner and compressed air, then replaced all the brittle rubber hoses at the ends of vaccum tubes. In the process I discovered the reason for the harsh shifts. The hose on the vacuum transducer on the tranny was so aged the metal line loosely fit inside it. After reassembly I ran some home made seafoam through the engine, confirmed vacuum signal to the EGR valve (got 5 Hg in. at cruise with light load) and today I went for a retest. Car passed with flying colors. NOx were 75 and the limit is 320 if I remember correctly.

    So, for those battling high NOx, it's not enough to replace the EGR valve, you gotta clean the all the channels which carry the exhaust gas to the intake.

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  3. #2
    The Gold's Avatar
    The Gold is offline Cadillac Owners Fanatic
    Automobile(s): 92 El Dorado
    Join Date
    Jul 2010
    San Francisco

    Re: EGR cleaning - high NOx during emissions test

    Mkoz, thanks for sharing this information.

    My 1992 Eldo (45K miles) has exactly the same NOX failure numbers !

    So, I just figured out how to remove the EGR valve (which is the original one) by using a 13mm crows foot wrench and a 3/8 inch drive extension and a
    similar 5" long breaker bar.
    I already cleaned the EGR stack tubes, throttle body plates and throttle body throat and will soon hit the 'ports'... hopefully my EGR valve is OK.

    Thanks again for the shared info !!!

  4. #3
    85fleetwdbrougham's Avatar
    85fleetwdbrougham is offline Cadillac Owners Member
    Automobile(s): 87 brougham d'e 81 S.D. (Sold) 85 fleetwood br. (Sold/broke)
    Join Date
    May 2012
    west petaluma, ca

    Re: EGR cleaning - high NOx during emissions test

    just failed nox by twice the limit origanal valve. got a new one. going to do some cleaning

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