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backfire? 850 1997

posted by  someone claiming to be Frank on  Tue Aug 4 15:29 CST 2009 [RELATED]

Recently I've been hearing a very infrequent "pop" which seems to be coming from the exhaust system. It seems to happen more often when I am cruising at highway speeds with little load on the engine. I did a scan and noticed that it triggered the famous 0172 code.

Could it be that unburnt fuel is finding its way into the hot exhaust and when conditions are just right, I get a detonation?

Any thoughts or suggestions? Thanks.

97 850 GLT soft turbo w/237K








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    backfire? 850 1997

    posted by  KlausC on  Tue Aug 4 17:09 CST 2009
    Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
    last visit: Fri Oct 24 10:15 CST 2014
    [RELATED]

    System too rich, P0172, is an indication of a leak in the vacuum system causing more fuel to be injected than needed. That will only happen on light loads and/or backing off the throttle. The excess fuel is then burned in the exhaust, usually in the cat.
    Ignoring the p0172 will eventually cause the O2 sensor to get coated and fail, and then the Cat fails.

    Go find your leaking elbows. It is not a fun job, but a mechanic will charge you a lot of time and may stop after the first leak when there might be a couple of them.

    Klaus
    --
    The more I learn, the more I forget. So why learn?








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      backfire? 850 1997

      posted by  someone claiming to be Frank on  Wed Aug 5 13:21 CST 2009 [RELATED]

      You were spot on Klaus. The rubber elbow at the manifold by the P/S had worked its way off. It seems the clamp had not been positioned correctly. A scan rerun seems to confirm that that was the problem. Thanks again for the quick and accurate diagnosis.

      Frank







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