Zackb911

Hey guys I finaly got around to taking my car for inspection and my fears came true it failed and pretty bad at that.... Heres the breakdown:

Reported Allowable
HC 1.75 2.00 PASS
CO 31.03 30.00 FAIL
NOx 6.17 3.00 FAIL
CO2 312.27

The NOx was really high over 30MPH. This was with my autothority stage 2 chips in, I should have had the Gurus in. And it was fully warmed up with a good 30min run on the highway. Anyway looks like time for a new Catalytic converter and O2 sensor. Anyone have any comments or advise? I plan on getting an aftermarket cat from some local muffler shop and isnt there a way to use a GM o2 sensor and modify it for our cars?

Thanks!
Zack

Jake951

You ought to be able pass the MA emissions test with either Autothority or Guru chips. I've done it with both.

You can get a pretty good idea if your O2 sensor is functioning correctly with a dumb and cheap A/F gauge (Autometer, VDO, etc.). If the A/F dithers around stochiometric while idling or cruising at light throttle, then it's probably OK. If it doesn't dither, then you may have a bad sensor or a DME problem.

A bad catalytic converter is also a possibility, although I would check the O2 sensor first because it's a rather common cause of failed emissions tests and is rather inexpensive to replace.

Danno

Yeah, both HC and NOx were high, which is unusual as they are inverse functions of each other. The typical tuning adjustment here is to richen up the mixture to increase HC which would then lower the NOx. But you're already borderline on the HC as it is, so I think this may rule out the O2-sensor. My bet is on the catalytic.

What's your compression? I may be possible to have so much carbon built-up that you have hotter-than-normal combustion, thus the higher NOx reading. Also using a colder plug may help as well. I kinda like the NGK - B8EGV plugs.

Zackb911

Danno- I havent done a compression check yet I need to borrow a gauge to do it. Think it might be wise to get one of those de-carbonizing cleanings that garages do by running detergent through your engine (I've heard of sucking brake fluid through the intake too??) I'll check my plugs (which are new) too are those NGK available at Auto Zone or Lappens? I have 60 days for a reinspect so Im sure I can get all this done:-)
If anyone else has anything to add feel free to chime in!

Thanks,
Zack

OriginalSterm

If you have not changed the oil in a while, and/or if you have had a lot of short runs on cold starts, you will have high HC's. Nearly 20% of the fuel on a cold start goes into the oil pan, and if you don't run the car very long the HC's never get vaporized out.

It could be possible the chips are causing you to run lean (high NOx) and the high HC numbers are from previous cold starts (lots of them). Tests I've done in emissions labs can be skewed from tuning and testing unless a recent (typically synthetic) oil change has been done. Some of the HC's may also come from oil passing through the system, although not likely.