timshug

I just barely failed the NO emissions at 2820 RPM on my 1985 GT Coupe (2.2 L / 5 Cyl.) The maximum allowed is 955 ppm and my car tested at 1085 ppm. Any suggestions as to how I could bring this emission down for a re-test without any major repair work?

socalclimber

Post your CO and HC readings and what the standard is for your test on each. Would like to see where all your values are.

Was CAT hot for test, i.e did you do a good drive before showing up?

Retarding timing 3-4 degrees MAY help your NOx value. CAT may be old and worn out. Other causes of high NOx: too lean A/F mixture, faulty EGR system, too much spark advance.

timshug

Thanks for the quick response. I learned today that I have a blown exhaust manifold gasket and that is probably causing the high NO measurements (1398 at 15 MPH and 938 at 25 MPH. I will have that fixed and then get another re-test. I replaced the Catalytic converter at 100K and car now has 130K so hopefully, that is not a problem. Tim

mt6127

check for intake air leaks as well. retarding the spark may help sneak you by but generally high NOs = lean burn and in these cars its signs of an air leak (ie around the intake boot, exhaust leaks like you noted, and even around the injectors (it was a pain getting to all five on my 4KQ, but I found a weed puller (that hand tool with a v notch in the blade) worked really well for popping out the injectors!! Good luck I think you're on the right track.

timshug

My emission problems were solved and I passed the smog test after I replaced the exhaust manifold gasket and a broken vacuum line.
Good for another 2 years!