emissions failed

I took my 1990 through today and I failed! They told me mytruck was running very rich. My registration is due december 29 so time is of the essence. I just put in a new Cat and Muffler last thursday. Ive also replaced the EGR valve and IAC. Ive also replaced the Head gasket and manifold gaskets. Would a new O2 sensor make that much of a difference? Im at a loss for ideas cause I dont really have the time or the money to rip apart the block to put new rings in. Someone Help!!!!

its worth a try at this point

I had the same issue. New O2 sensor, and I passed with flying colors!

http://naxja.org/forum/showthread.php?t=976348
This one has some good stuff in it

I don't know about CT smog requirements but here in CA they're pretty tight. I totally failed smog several years ago and this is what I did then, and what I was told to do by the local Jeeper shop.

1. Replace O2 sensor (it's a 90 like mine so only one +/- $50).
2. Check and replace all questionable vac lines and grommets.
3. Blow out your CCV tubing and grommets with compressed air (even the computer "air in a can" works well.
4. Buy a NEW gas cap.
5. Get a can of G2P (Guaranteed to Pass) and run it through a full tank (follow the instructions).
6. Take the Jeep in after you've taken it for a high MPH spin and it's good and warm.

A quick tune up (plugs, cap, rotor etc.) and oil change can't hurt either.

Get back to us!!

ParadiseXJ said:

I don't know about CT smog requirements but here in CA they're pretty tight. I totally failed smog several years ago and this is what I did then, and what I was told to do by the local Jeeper shop.

1. Replace O2 sensor (it's a 90 like mine so only one +/- $50).
2. Check and replace all questionable vac lines and grommets.
3. Blow out your CCV tubing and grommets with compressed air (even the computer "air in a can" works well.
4. Buy a NEW gas cap.
5. Get a can of G2P (Guaranteed to Pass) and run it through a full tank (follow the instructions).
6. Take the Jeep in after you've taken it for a high MPH spin and it's good and warm.

A quick tune up (plugs, cap, rotor etc.) and oil change can't hurt either.

Get back to us!!

Click to expand...

The O2 was the only thing i havent changed yet.
Vac lines were all checked about 2 months ago looking for a gremlin.
Those were replaced about 6 months ago but im going to clean them up.
Gas cap test failed so a new one is need anyway.
G2P can be found at all major autoparts stores?
Truck was good an warm when I took it in today.

Tune up was done on it when I had that gremlin so plugs wires cap rotor are under a year old and prolly have under 3000 miles on them.

My HC and CO levels were just about double of what the limit is.
HC Limit (PPM) 160/ Emissions: 319
CO Limit (%) 3.24/ Emissions: 7.59
NOx (PPM) 4200/ Emissions: 70 PASS

Swapping the O2 is what fixed mine when I failed and my numbers were very similar to yours. That's defiantly the first thing I would try.

I know I'm bringing up an old thread but I have the same problem. I've done all the checks minus replacing the O2 sensor At least with a new one! I realize that could fix it but I have something new to add.
This was my 3rd fail on this vehicle in three months time. Each time I have found something that may have been the problem and done work to it.
Jeep has a new cat, but was running so rich when I bought it that you could smell the unburned fuel coming out the exhaust. I swapped in another O2 sensor I had laying around after finding from the first test that I was at 60 something % unburned fuel out the tailpipe....not good on the wallet.
Next I found that the coolant temp sensor wasn't even connected (this jeep just had a full drive train swap from another 89 Cherokee (same year).
Then smoke tested the vacuum lines and found no problems.
Replaced engine coolant tank cap (actually whole tank...another story)
Gas cap test passed so I left it alone.
Tested but engine was barely warm. Failed test. But only CO2 this time and only by 3%, Nox was in range now.
Checked for more vacuum leaks, EGR valve is new. Replaced IAC with a known good one (from another Jeep of mine). Found a leaky throttle body gasket and replaced it. Checked everything over again for good measure and went back again yesterday after warming up engine very well and a high speed run down the freeway to get there.
FAILED worse! Co2 was double 53% this time and NOX was double it's last test as well and out of range again.
I'm down to testing everything that controls the mixture through the computer today. MAP, TPS, CTS (again), MTS. And I'll replace the O2 sensor.
If anyone has anything to add to what I can do to figure out this demon please chime in!
I'm about to sell the Jeep after dumping a ton of time into getting it set up the way I want for wheeling, just so I don't have to worry about Emissions on this one.

HELP!

when mine failed i replaced the o2 with a NEW one and replaced my MAP as well. passed easily. the MAP couldnt hurt, its cheaper than a new o2 sensor.