1991 240SX failed emissions test

[rogoman]

Need an opinion on whether changing to a CATCO high flow CAT caused me to fail emissions testing.

I installed a CATCO high flow CAT about 2 years ago. Here in New Jersey, inspection is every 2 years. Today I went for inspection and it failed emissions. I had installed new spark plugs and new air filter about a week ago so it's not that.

Measured the resistance of the ECU temperature sensor and that was OK.

Here are the readings from the inspection station:NOx: Standard: 1045Reading: 1264

HC:Standard: 136Reading: 139

[elwesso]

Did you disable your EGR? Thats probably why your NOx readings are so high... HC is just barely over the limit, so you could probably get it to pass...

best thing to do is get the cat as hot as possible right before the emissions test. Drive it hard on the highway for 10-15 mins before taking the test and if you have to wait in line, let it idle high (1500RPM) or so to keep it hot...

An old trick I heard of is if they dont pass retard the distributor all the way.

[skydragoness]

I'd try replacing your 02 sensor and make sure the wiring for it is okay. The cat didn't cause it. Check your timing too, should be 20 tdc.

[wheelsspin]

The EGR system is designed to control NOx, so that is the best place to start. Check vaccum lines to and from, and pesky carbon buildup at the EGR and it's piping. Another cause of high NOx can be lean mixture. Check fo vaccum leaks - a bottle of propane or the like over the hoses makes the idle change if you have a leak. One more thing - overadvanced timing could do it to, so set it back to factory spec if it is out. All of these would also cause the higher than normal hydrocarbons.

[MaximA32]

Matt, you're my hero. Emmissions stuff pwns me.

[wheelsspin]

I hate emissions stuff. There are many things that can cause a car to fail. Just got to work your way down the line of possibilities. Start at the most common and work to the rare and strange.

[rogoman]

Thanks everybody for your input. I'm starting with the EGR tests in the FSM.