I have a recently purchase a 1999 S70 non-turbo with about 98k miles that has failed the required emissions test twice with very high NoX readings >3000. After the first test a diagnostics scan indicated a failed rear O2 sensor. That was replaced with a model specific unit and a retest was done with no improvement at all. HC and CO are very low but NoX is still >3000. Upon close inspection today after the second test failure I found that the PCV elbow behind the power steering pump going into the intake manifold was rotted off causing a big vacuum leak.
Would this cause such a high NoX reading. The car is running excellent, idle is steady at about 900 rpm and the engine does not appear to be running hot. It is being recommended that a catalytic converter efficiency test be performed next. This was before I found the rotted PCV line elbow.
Any help or guidance would be appreciated.

 

Yes, a vacuum leak could cause increased NOX since it is leaning out the fuel mixture, but I would think the ECU would compensate for the vac leak (that's why it seems to run fine) and if the vac leak was too large for the ECU to compensate for, then I would think it would set a fault and turn on the CEL.

Suggest you fix that (and any other) vac leak, then go from there. Are emissions retests free in Canada? They are here...

Keep us posted..

 

No CEL's at all!! Emission retest's are $18.75 each. I have repaired the rotted elbow that I found yesterday and am now looking for hte second one that I have read about just behind the motor on the drivers side that is supposed to fail as well.

That's why I am so disappointed in myself for buying the car as-is. If I had insisted on the previous owner certifying it within a negotiated price then he would have been on the hook for this problem.