Failed Emissions

[srkruger]

So I took the jeep that I just purchased to get emissions today and it failed. It is putting out to much NOx. The allowable ppm is 1110 and it is putting out 2378. Before i go and get it check out and waste 100 bucks does anyone have any suggestions on what this could be or what I could possibly replace to get it to pass? There is no check engine light on, its a 1994 XJ, 200,000 miles auto. 4.0

[5-90]

Start with your cat - it's 12 years old. Since you don't have an EGR system, that would be my first thought.

Next after that? HEGO sensor. If you're anywhere around 150Kmiles and it's original, you're probably due. Don't bother with the "downstream" sensor (if you have one - I'm not sure when they started that nonsense...) but the "upstream" one will probably be the problem, if the cat doesn't fix it.

5-90

[srkruger]

thats what i figured, what about the o2 sensor? I was thinkning if the o2 sensor was faulty the check engine light would be on correct?

[5-90]

Theoretically, yes. However, if the sensor is on its way out but not failed, it may not set a CEL/MIL. Yet another reason to start with the cat...

5-90

[XJ Beater]

pfft, i was puttin out like 4000ppm or somethin, fuel injection cleaner deal at the mechanic and a few tweaks here and there and it passes fine now

[carnuck]

Oil change, CORRECT spark plugs, make sure dist is indexed correctly (I see that a lot), good EFI cleaner (BG's 44K works wonders!), clean the throttle body and idle air circuit with throttlebody cleaner. Thermostat sticking? NOx is produced from combustion temps being too high. SOmetimes even an aftermarket air tube can cause them to skyrocket.

[srkruger]

I doubt its running to hot because I have wired electric fans and the temp doesn't get over 150. I just put a new dis, wires and spark plugs on. Tonight I am going to put a can of fuel injector cleaner in and hope it passes tomm. The cat is not rattling or anything which makes me think it is ok.

[POSXJGuy]

i failed the NOx part of the emissions kinda like your readings and a new O2 sensor had me pass easily the second time around. i had the cat replaced about 3 years before that.

good luck, should be a simple fix.

[Dan1990XJ]

I worked for the ohio emissions testing run by envirotest and a simple o2 sensor usually fixed this for everyone. Also in the future, after you pass this test, put the jeep into part time 4 wheel drive before you enter the station and tell them it is stuck in four wheel drive and that if it comes out it, it will not go back into gear (they shouldn't question it) then they will give it an idle test instead of putting it on the dyne and this test does not test for NOx. I worked there for three months and never saw anyone fail an idle test.