My 1993 Volvo 940 (Regina) did not pass emissions test, here were the readings:

Hydrocarbons - 2.2 (has to be under .8) - Failed
Carbon Monoxide - 9.3 (has to be under 15.0) - Passed
Oxides of Nitrogen (NOx) - 4.5 (has to be under 2.5) - Failed

This car runs fine otherwise, pretty smooth idle and has power at all RPM ranges, and the service light is off. The air filter is not new, but not really that dirty enough to fail I would think, but I will replace that before the next test anyway. The car has new cap, rotor, and spark plugs. I have not replaced the wires yet, but will do that as well before the next test. My other 94 940 passed but I run premium in it, wonder if that would help this car.

Any other suggestions? Do these reading indicate I need to replace my fuel injectors or my CAT?

 

Your car's running rich. Exhaust manifold leaks, intake manifold leaks, vac line leaks are all common reasons. The O2 sensor could be bad, the engine coolant sensor could be bad. High NOx is indicative of high combustion chamber temps. Generally, that is a result of a bad cat or clogged EGR. At some point, I think all got the EGR but not sure if that was the case w/o searching for the 93 year model. Check the other stuff first; the NOx may come down by itself. No...you don't need injectors.

 

Thanks for the suggestions. Glad I do not need new injectors, they cost about as much as I paid for the car. Pretty sure this model does not have the EGR. There is nothing attached to the exhaust pipe until the O2 sensor.

I'll go through and replace all those rubber elbows and I's for all the vacuum lines. Some are a little cracked anyway, but nothing that looks like it has a hole in it. I did have bad exhaust manifold gaskets that were leaking, but I already replaced those, and the engine is all around pretty quite now.

You may be on to something with the engine coolant sensor. I did not realize there is the one for the gauge and for fuel injection. I am also have an issue with this car randomly dieing, not being able to start the car hot, along with 16-17 mpg, and the car had to be cranked a little more than usual on a cold start, all the symptoms for a bad ECT. This might just might solve both issues.

 

It ended up being the CAT. It passed the test real quick. Everything else checked out.

 

Thanks for the update.