I have a great little 1988 volvo 240 sedan with 154,000 miles on it that just failed to pass Texas emissions in one catagory only. It's putting out about 2050 ppm in NO's. I had the mechanic "flash" or clean up the motor, but after rechecking, it changed nothing. Any suggestions or direction ? BTW, it passed last year and has only been driven 2000-3000 miles in the last year. It's just an extra car. Thanks in advance, ljs
My uncle had this problem with his '84, and tried some Goodwrench (from a GM dealer) top end cleaner, which helped a little. Those 240s generate a lot of NOx and need a good functioning convertor. The problem is the ignition system runs on the ragged edge of maximum advance which creates high combustion temperatures which is when NOx form. This improves fuel economy slightly. What you can do is disable the vacuum advance going to the ignition computer, which will make the computer use the full load map at all times. This retarded timing lowers NOx formation, and you probably won't even notice any mileage difference. Just disconnect the vacuum line going to the ignition control unit (mounted on the windshield washer bottle), if the test center is going to be upset with a disconnected vacuum line, just put a correctly sized ball bearing into the hose and reconnect.
There's something else wrong, my mom's '86 has a gutted cat (insides crumbled) and it puts out very little NOX and passes very easily.
Here were the test results: 25mph / 15mph
HC= 120ppm (162ppm allowed at 25mph) / 125ppm (167ppm allowed at 15mph) passed. CO%= 0.70 (1.04 allowed) / 0.70 (0.94 allowed) passed. CO2% 14.4 / 14.3 passed O2%= 0.6 / 0.7 passed Nox (ppm)= 2091 (1163 allowed at 25mph) / 2305 (1273 allowed at 15mph) failed. dilution= 15.1 (>6.0) / 15 (>6.0)
So what do you think ? Bad Cat and/or O2 sensor ? Nero
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