93 Ls400 Can't Pass Ga Emissions Test

[Buffalo]

Car runs flawlessly with 140k on it. Here are the emission numbers from last year (1869RPM) and this year at RPM settings of 1898 and 1399.

25/25 test

3/2005 3/2006 3/2006(1399RPM) Allowed

HC ppm 101 111 128 103

CO% .27 .30 .27 .57

NO2 ppm 298 703 868 712

RPM 1869 1898 1399 2500

CO+CO2% 14.7 14.4 14.6 6.0 min

50/15 test

3/2005 3/2006 3/2006(1399RPM) Allowed

HC ppm 81 119 131 107

CO% .27 .31 .28 .59

NO2 ppm 233 661 868 786

RPM 1918 1965 1432 2500

CO+CO2% 14.7 14.4 14.6 6.0 min

After failure we replaced spark plugs, wires and got fault codes for mass air flow sensor. We replaced the MAF, got no more fault codes, retested, and got virtually the same test numbers as before the repairs. The catalytic converters are original. I run 10w30 full synthetic oil and again the car runs fantastic. Where do I go next? My next thought was the catalytic converters. I wouldn't think it would be an 02 sensor. If it is the Cats are any of the aftermarket Cats any good? Thanks. Mike D.

[Sweet95LS400]

I would say change the 02 sensors. At least the 2 main ones. They are only good for about 90k, at this point they dont owe you a dime.

[Buffalo]

I would say change the 02 sensors. At least the 2 main ones. They are only good for about 90k, at this point they dont owe you a dime.

Lexus diagnosed my problem as bad ECU. They quoted 1100.00 to replace. Any suggestions?

[monarch]

I can't imagine the engine would run fantastic with a bad ECU. I'd replace the two distributor caps and two distributor rotors and the two oxygen sensors that are ahea of the catalytic converters (not the ones behind the converters) . Then your emissions will go down noticably, but if the NOx still stays high then you have trouble with the EGR vacuum modulator or EGR valve itself. Replace catalytic converters as a last resort.