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bad NOX reading / EGR/ pulse air system 900

posted by  norfleet on  Mon Aug 30 19:03 CST 2004
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last visit: Thu Dec 26 15:33 CST 2013
[RELATED]

I just failed the ca smog (to high NOX). This is a 1994 940 (straight 4 banger, no turbo) with 160000 miles. The heads were redone about 10,000 miles ago, the cooling system was also redone (new radiator, thermostat, etc).

NO codes were set and the EGR manually works (when apply vacuum - engine stumbles). Can the EGR system be bad withouts setting a code? The radiator temp was about 190F (where it should be). The HC and CO readings were fine (suggesting that the O2 sensor is working).

The volvo service manuals cover the EGR system, but I cannot find any info on the Pulse air system. How does one check the controls for that system? Also, how does one check the cat converter? If the HC and CO reading are OK, does this imply that the cat converter is also OK?

Any ideas on what to check for a bad NOX reading (beyond what is mentioned above)?






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