Had my emissions test after changing the cat. Still failing NOX. So far O2,cat, rotor, plugs and dist.cap have been changed. Time to call my buddy at the local Volvo dealership.

The FF. is a major cause of NOX failure.

1.overheated engine
2.lean air fuel ratio
3.vacuum leak
4.overadvance ignition timing
5.defective EGR

check every single one and 'am sure you'll fix the problem. Happy New Year!!

My Volvo doesn't have EGR beleive in 1990 only Calf. cars had it. On the igniton timing what would cause overadvance? Possibly knock sensor bad?

Since Ignition Timing isn't adjustable, and you have no EGR, it's most likely a combination of the usual (more common) suspects...

Vacuum leaks usually cause a Lean air fuel ratio, and lean running = Hot running.

--
Bruce Young,
'93 940-NA (current)
'80 GLE V8 (Sold 5/03)
'83 Turbo 245
'76 244 (lasted only 255,000 miles)
73 142 (98K)
'71 144 (track modified--crusher bound)
New 144 from '67 to '78
Used '62 122 from '63 to '67

thanks for the inputs. Will be checking all intake manifold and injector seals for leaks. Going to check the knock sensor as this is an input to the ignition control. Also read that if the fuel presure is to low it could lean out the mix.

I also failed nox in Mass. changed everything.... bricksters suggest that you check for vacuum leaks, that the O2 has elect., that the master idle adjustment is adjusted , that the temp. sensor is good... I will have the volvo guy try some magic, then I'll report to bricksters, one and all... try to have a happy and healthy!

By how much?

Did you try retarding the timing?

Have heard that wood alcohol (methyl alcohol/hydrate) added to gas will help. Available in paint section.
--
1980 245 Canadian B21A with SU carb and M46 trans

The NOX reading was 4.60 with a max of 3.25. My car is a 1990 and my understanding is that the timing is electronically controlled.