1986 Volvo 740 smog test failed

1986 VOLVO 740
340,000 MILES • 4 CYL • 2WD • AUTOMATIC
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YIP
  • MEMBER
  • 2 POSTS
Hello.
My car was failed for smog test emissions (NO (ppm))
15 mph max 1125 ave 399 meas 1591
25 mph max 955 ave 332 meas 1276
After to replaced a new catalytic converter the retest results was:
15 mph max 1125 ave 399 meas 1360
25 mph max 955 ave 332 meas 1131
Failed again. Is anyone can let me know what happen may cause this problems? the Oxygen sensor? the air mix sensor? Or.....？Thanks!
Yip.
Apr 1, 2008 at 5:42 AM
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EDRUNNER
  • MEMBER
  • 4 POSTS
Check for clogged or bad EGR valve causing high NOX making the engine run hotter. EGR valve problem is the No.1 cause. Clean the tubing or ports and valve or replace it. Also check wire connections to make sure it operates (opening and closing). Also check cooling system for engine overheating which contributes to the problem.
Aug 2, 2009 at 8:13 PM
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