Hi there!

Would love to hear from you if you have gone through this and what you did. My sweet, 1991 Volvo, 740 Turbo/Intercooler wagon has failed smog and a preeliminary test, too. Apparently, the Nox is high, in the 1400s. It has 280, 000 miles and I am a broke teacher. I have until June 24 to repair it or see if I am eligilble to surrunder it to the DMV for money.

What have you done, or would do? Invest and keep it or sell it or try to turn it over to the state for money?

Otherwise, the car is wonderful besides this problem and it needs new front brakes, a tune up, an oli change-ah!

Thanks,

Teacher in California

 

Personally.

I would move out of california.

other than that I can't help you, sorry. :/

 

High NOX indicates a lean fuel mixture. I would first off get the car thoroughly serviced (also find somewhere that knows how to read and diagnose the codes from the fuel injection system), dump a bottle of fuel system cleaner in the fuel tank and have the fuel filter replaced too. An oil change always helps with emissions too.
What is the fail ppm for NOX in the testing?
To be honest, your car probably just needs a major service, getting rid of it won't solve much, as you'll be up for another used car that will also need servicing work. You won't get much for the car if you turn it in or try to sell it, so you'd have to find money for another car anyway. Any money you spend on this car right now for engine servicing will yield good results in improved mileage, so it's probably a good thing in that respect as well.
At least a 740 turbo is generally quite affordable to maintain and repair, they also last a good long time. So I would suggest spending the money on the devil you know as it were.
Front brakes are pretty cheap on these cars compared to many others as well.

 

Welcome to the forum.

I agree with Typhoon. Do a full stage zero to her and she will be find. When was the last time it had a good overall?

 

Try taking a look at the Brickboard. Do a search there for NOX and you will turn up several good writeups from people with the same problem as you. I did a quick search and this turned up:

RWD - Cure Found for 1985 245 High NOX Emissions

Good luck

 

Turn it over to the state? Are you mad? This would be worse than dropping off your first born at the steps of the Salvation Army! Never!

 

High NOx is a result of combustion temperature being too high. While a lean condition will certainly bring about elevated combustion chamber temperatures, typically it is a failed/failing catalytic converter and/or a faulty or clogged EGR valve that causes the higher temps and NOx production. Turbo cars typically run rich. Rich fuel mixtures kill O2 sensors. With a dead O2 sensor, the car will default and run even richer, which leads to premature catalytic converter death. The long term solution has been laid out above. Your car needs some TLC (and money) spent on it. Just guessing but...probably need 1. O2 sensor 2. Catalytic converter 3. Service/replace the EGR valve (if it has one).
Now...for the short term solution (since you said money is tight). The engine timing for your car is controlled electronically with no way to adjust timing traditionally by turning the distributor. If you could retard your engine timing 4-6 degrees, most likely it would lower NOx enough to pass. This is not a permanent fix; it is a band-aid solution at best. Air quality is important, especially in Cali. Bad dirty air will kill trees. Dead trees means there will be none to hug!!
OK...here it is...Jot this down for your mechanic. Tell him to find the ignition control unit (ICU). Typically, it is black...occasionally gold colored. Tell him to ground pin #19 to pin #11 or #12. 11 is the ground for the crank sensor, 12 is ground for the knock sensor. No harm will come from this. By grounding pin #19, you will retard static timing 6 degrees, combustion chamber temps will drop and so will your NOx. After you pass, take it back to the tech and have him remove the jumper wire. Your car will be SLOW with the ignition retarded!!