I own a 1988 Volvo 240DL and I've had difficulties getting this car to pass smog. The only emisssion it's running high on is NOx. It's about 1750ppm when the max should be around 730ppm.. What should I look for? I've replaced some cracked hoses, but I'm not sure what else can be done. A new oxygen sensor was installed last August, along with a new catalytic converter, new upper intake, and new fuel injectors. What should I attempt now?


...Also, the service tech informed me that my timing was set at 0ยบ. A month ago it was set at 10ยบ and my car hasn't been touched. How did the timing readjust and what should it be set at?

 

First things first check the lower crank pulley because they like to spin when they get old. Then every time you check the timing it will be diffrent.One way to check is make a mark on the pulley from the out side of the pulley to the inside.Take the car for a ride shut it off recheck if the marks dont line up the pulley is spinning and you will need a new one.Second check for any vaccum leaks on the intake or in the lines.check that first and then let me know

 

I will definitely check out the pulley tomorrow. How much is it cost wise to fix the pulley? Easy fix? And what should my timing be set at?

As for vacuum leaks, I've inspected and replaced some cracked and brittle hoses, but I'll inspect for more.

 

You might want to check with your local volvo repair shop.You need either an impact gun or a special tool to hold the crank pulley to get it loose.It's not that bad otherwise just removing the V-belts then the crank pulley once the bolt is loose you can work the pulley off. i will check on the timing tomorrow and let you know.

 

Besides a vacuum leak, what should I look for? I know the high NOx readings are probably caused by a lean condition, but I cannot determine what is causing it. Could the timing be anything to do with it?

 

The timing on your car should be set at 10 +- 1 degrees your car should have an adjustable mass flow sensor that can be adjusted to help drop the level of NOx but then again it might have to go to the shop and they should have a machine to probe the tail pipe and help adjust the senor to drop the readings.Also just a stupid quiestion but i've seen it make people fail to but have you changed your oil lately? I have seen people fail they change their oil and go straight back then pass with flying colors.

 

I'll probably end up taking it to a mechanic. The oil was changed about 500 miles ago.

 

If you have an adjustable air flow meter you can try to adjust it your self by using a volt meter.Put the positive lead on the green wire from the o2 sensor and the ground lead to a ground.Then adjust it till you have it to about .50 of a volt and it will lean it out.I think you might be running to rich now.Sorry i couldn't help you more.

 

But high NOx is normally caused by running lean. My other emissions are very, very low.

 

I could be wrong on you running lean i forget which readings are which its been 6 years since i have had to worry about the readings since Florida doesn't have emissions any more.You can still try to adjust the mass flow meter but adjust it to about 1v or a little over that should make run richer than it is now as long as it is set at that now.I will try to find out more answers for you in a day or so.