Question about 1998 GMC Jimmy
Your Jimmy is running rich, air fuel ratio is not correct. Start with cleaning your MAF sensor, a dirty MAF sensor will cause your engine to run rich or lean, other causes would be a faulty fuel pressure regulator. Start with the simple and to common and try cleaning your MAF sensor, you can pick up a can of MAF sensor cleaner at most auto parts store like Auto Zone or Part Source.
Also make sure your engine is running at the proper operation temperature 190", cold running engine will cause the ECM to run your engine rich. Causing the back soot and fouling up your spark plugs and intake ports with carbon.
The ECM was programed to recognize the 4.3 vortec to run at 190" and anything cooler will cause it to run rich and poor on economy.
Thank you for using fixya and good luck.
Posted on Apr 27, 2010
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Posted on Jan 02, 2017
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