Expert: chris ehlerman - 11/7/2007

Question
I have a 1999 Grand Am with a 3400V6.  Emissions tests results in consistent high NOX (HC & CO are very low.)  I have changed cat, replaced egr, cleaned throttle body (and AIC), replaced rear 02, used GM cleens (combustion chamber cleaner).  The only ecm code i have is 442-evap leak.  Temp is correct, and readings now are all normal thru a Snap On scan tool.  What else is left?

Answer
hello jay i know you said you replaced the egr valve but did you check with the scanner the proper operation of the egr system. it could not be opening or many times the passage way gets clogged with build up preventing exhaust flow to the intake. also is the car being emission tested on a dyno. if so make sure you have a high velocity fan installed in front of the car. many cars run to hot on the dyno without the fan an will have increased nox readings. also check your evap system it may be creating a small vacuum leak into the intake. follow the test procedures for the po442 code. if you do not have access to the troubleshooting procedure email me at cardoctorc@aol.com with your fax number and i will send it to you. good luck