Didn't pass the emissions test - help diagnose the problem?

[YELLAHEEP]

Ok, I went to the emissions testing facility and my jeep failed. Now I need to get the repairs done within 10 days to keep from having to pay for a re-test. Here's what the printout said the test limits and results were:

The first numbers are the limits and the second are the results:
HC gpm = 4.000..........4.7023
CO gpm = 25.0000......27.7562
NOx gpm = 9.0000......9.2414

Now, it was around 40 degrees outside and the Jeep was at operating temperature. But, I've never made a habit out of going to the test stations when it's that cold out in the past so I don't know if it's more likely to cause a test failure with it being that cold out. The kind of test Colorado uses puts the vehicle on a dyno and the equipment sniffs the exaust while an operator "drives" the vehicle at different RPM's and speeds.

I'm thinking that in order to cure these problems, I'm probably gonna have to replace the Oxygen sensor, and then tune it up with plugs, wires and such.

Any other ideas? Things I should check or fix?

Thanks in advance!
Troy

 

[rixXJphx]

Damn, you are so close all across the board!





Usually, one item is high and the others are well within limits.

First: Try just the plugs and dist cap/rotor.

Next, O2 if it's over 50k.

Then, ignition wires.

Finally, cat.

-Rick

 

[Fred]

Change oil. Change O2. Have it good and hot.
Fred

 

[mudhound32]

I ran into the same problem last weekend when I took mine in for an emissions inspection. I changed the plugs, wires, rotor, cap, and new cat in the last 2 months and still failed with higher numbers then you had. I will be changing the O2 sensor and the oil since I just hit 3k from the last change. Let me know how much your numbers go down aftet replacing the sensor. I already picked up the O2 sensor but probably won't get it in until the weekend.

 

[Eagle]

Bad O2 sensor usually results in a rich mix. That would certainly cause high Hc readings. High Nox is often caused by running a cold thermostat -- are you running a factory 195 or have you fallen for the hype that says a 180 or a 165 is "better"?

It is unusual to have all three over the limit. As noted, usually one fails and the other two are fine. Do you get one free re-test? If so, I'd do plugs and O2 sensor.

Good luck. Please post what you do and the results.

 

[8Mud]

Sorry this isn´t really a highjack, but not really an answer either. I wonder what a restrictor gasket would do, installed between the throttle body and the manifold. Say about 15-20%. And/or an adjustable MAP, to lean things out awhile, just to get a body through the test. The test here, has different values, for different vehicles and model years. You just have to pass your catagory, there are some absolute high values, that can not be exceded, but these are in the range of an oil burner or a totally failed cat. I installed a 212 or a 220 thermo (I forget) for the last test, that seemed to help across the board a little.
Also wonder, what a higher octane gas might do. Even maybe an octane booster (cat friendly). Might lower the HC some?
We use one XJ around here, to pass the test for about a dozen other XJ´s. Everybody is close, but just can´t quite to seem to make the grade. So we resort to skulduggery.

 

[HossHoffer]

Close

As said you are close enough on all the readings that a good tune-up i.e. plugs wires, and a new O2 sensor should put you right in. Make sure you are good and hot! I would get a fresh oil change just to make sure.

 

[RTicUL8]

I just had my '93 XJ (4-banger) inspected yesterday in Boulder. The temp was about 60.

---->Limits------->Actual Reading
HC GPM = 4.000..........0.5955
CO GPM = 25.0000......4.2530
NOx GPM = 9.0000......0.5762

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The only thing I did first was to change the oil and run thru a couple of tanks with fuel injector cleaner.
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