Question re. 240 emissions

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

 

What are your other readings ? Check for vaccum leaks and retard the
timing slightly . Most likely it is time for a new catalytic converter
.. The aftermarket direct fit converters are around $ 100 -
www.fcpgroton.con , www.autozone.com

 

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.

--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

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