How can I reduce hi emissions?

I just got back from my emissions test and have some hi readings which caused a failure. The mechanic suggested I change the O2 sensor. Here are the numbers the jeep posted:
HC 4.27 gpm
CO 91.21 gpm
NOx 2.07 gpm

Here are the acceptable numbers:
HC 1.60 gpm
CO 40.00gpm
NOx 2.50 gpm

Before I had it tested I changed the plugs, wires, rotor, cap, air filter and added techron to my last fillup.

In addition to the O2 sensor, (which was never changed and has 210,000 miles) I was also thinking of changing the following since the Jeep when warm seems like it misses a little and sputters. I also have an intermittent startup issue and if I unplug and replug the tps it will start up.
-tps
-cps
-fuel filter
-oil change

Does this sound like it will bring down the numbers above? I have an 89 XJ auto, 4.0L stock

HCs

Seeing how the hydrocarbons are the only thing high then the O2 sensor would be a good place to start. Make sure you're nice and hot before going in. How many tries do you get?

a new O2 sensor will make a world of difference.. an oil change too if its due.. i wouldnt jump at the TPS or CPS just yet.... make sure the engine has been running at full operating temp for at least 20 mins before your test too.... another "shade tree" fix to reduce emmisions is to add a few bottle of isopropyl alcohol to the tank... my freinds father used that method to get all his junkers thru the "sniffer" test.... i would say it probably increases the combustion temp quite a bit.... that tells me burned valves are a danger.. but in a junker you dont care much about its not a big deal i suppose....
mike

How much isopropel<sp>

How may bottles per a full tank? I am ready to try about anything. The dealer says the O2 sensor is just fine. My limited is high on CO am replacing plugs and wires. Will pull the air filter prior to next test.

A friend with more cars and trucks than fingers and toes mentioned some sure pass to add to the tank. I haven't went out to get it yet.

He also mentioned some things in the way to take the test that apply to the WA style test. They use rollers here. You have to get it up to a specific RPM range for so many seconds. He says that during this test keep it just barely at the minimum and even let it fall below occassionally if you can get away with it. They will just tell you to speed it back up. He says the most important thing is to not just pull your foot off the accelerator when you are told to stop for the idle portion of the test. He says to let it down to idle as slow as possible.

I am going to follow his instructions religiously on Monday morning and am still open to any other suggestions. Emissions testing seems to be less logic and more like some kind of vehicular alchemy.

Marc

My Comanche wouldn't pass its smog test because of impermissibly high carbon monoxide and elevated hydrocarbons--a symptom of a rich fuel mixture. I ended up replacing the oxygen sensor (mine had at least 140000 miles on it) and the problem was fixed.

Erik
88 Comanche

I usually change the 02 sensor, before every test (not that expensive). Make sure to take it for a good run, up the interstate before the test. Double check the vacume lines and tightness of the intake bolts (and nuts). I´ve stopped with the gas tank additives, the fuel injector cleaner, I usually add, messed with the 02 readings, which may or may not, have messed with the unburned hydrocarbons? I unplug the aux fan and have been known to change the thermostat, to a higher number before the test.
I also make sure the small crankcase ventilation tube is open and clean. Excess oil vapor, also shows up, as unburned hydrocarbons.

had same issue

Same reading with my '90 XJ, 135K miles.
Slapped on new O2 sensor and passed with room to spare. And I've passed again since that happened two years ago.
My 2 cents: replace the sensor and re-test before you go spending money on snake oil remedies.

Thanks for all your replies. unfortunately the first test was a $35 dyno test and I got to keep my sticker, but the next thime is the real deal so if it fails again they are going to yank my sticker (which by the way will cost another $35). Glad to hear my mechanic isn't trying to yank my crank and sounds like replacing the O2 sensor and and oil change will get me the "Holy Grail"

Any suggestions as to pitfalls to look for when replacing the O2 sensor? Should I steel clear of soaking with a penetrating oil etc??

O2

Just be careful you don't pull the wires out of the sensor. They make 'special' sockets for them but I've never had to use them. Any penetrating oil will just burn off so go ahead and use it if needed. Good luck on the test.

also check to see if the egr valve and the catalytic convertor are ok.

89xj said:

also check to see if the egr valve and the catalytic convertor are ok.

Click to expand...

I had the exaust replaced about 2 months ago along with the cat so I don't think this would be part of the problem. As for the egr valve is there anyway to make sure its clean? I can almost remember something like pulling it out and cleaing the opening with a pick or other small object? Is this the recommended way?
Thanks