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1998 Pontiac Grand Prix OBD Codes

Tiny
ALBR12
  • MEMBER
  • 1998 PONTIAC GRAND PRIX
Computer problem
1998 Pontiac Grand Prix 6 cyl Front Wheel Drive 166000 miles

98 Grand Prix 3.8L giving trouble codes 305 (cylind 5 misfire), 420 (Catalyst system efficiency below threshold), and 1404 (EGR Solenoid control faulty). I replaced plugs and wires about 40,000 miles ago. Also around the same time replaced upper intake gasket (during which I bent the fuel rail, broke an injector (cylinder 1)and crumpled the EGR tube, all of which have been replaced). To add icing on the cake I was duped into a universal catalytic converter by a discount muffler shop(now I know better) This sounds like a disaster but looking for any insight of where to begin. Thanks
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Thursday, August 13th, 2009 AT 6:01 PM

1 Reply

Tiny
MMPRINCE4000
  • MECHANIC
  • 8,548 POSTS
Check spark on #5 by removing plug and grounding against valve cover, look for a blue snapping spark.
You have to find the cause of the misfire first, as it can cause the CAT code.

Remove and clean the EGR, but it may need to be replaced if solenoid is bad.
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Friday, August 14th, 2009 AT 8:58 AM

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