Failed Smog... :(

So my new 90 xj failed on the 15mph and barely passed the 25 mph

15 mph HC MAX 143 AVE 34 MEAS 145 CO MAX 0.73 AVE 0.11 MEAS 1.43
25 MPH HC MAX 103 AVE 23 MEAS 103 CO MAX 0.93 AVE 0.10 MEAS 0.74

So i replaced the O2 sensor and will replace all the plugs, I am also planning on swapping my cat from my 88 as I cannot afford a new one right now (they also appear to not be able to sell right now??)

Any other things you would recommend before i go back and retest.

I have already replaced the oils and sea-foamed and cleaned the TB out.

When you go to smog it make sure there are no fuel injector cleaners or any other of those usless products that you dump in your gas tank. Fill up w/ name brand gas, like shell, just normal 87. Dont drive it hard at all the last few blocks. My smog guy always says Jeeps are better to smog cold which is the opposite from the norm.
If you still cant pass there are som other little tricks you can do. Like drilling a 1" hole in the back of your muffler. Its perfictly legal, makes the stock muffler sound like a quiet flowmaster, and will allow a tiny amount of exhause to excape before the tail pipe which is where smog shops put theit testing equiptment.
Other than that youve done everything else correctly.

Mine failed to. passed the 15MPH and almost past the 25mph. I need to replace my computer before i try it again.

Ok well i guess i will just swap cats and get new plugs, and run a fresh tank of gas though it...

There was a write up about a month ago about this..He found out about some plugs to use..Do a search, I wish i could think of the tread name/I know it had failed in it..

Found it, check this tread out..http://www.naxja.org/forum/showthread.php?t=976348&highlight=smog+test

Grimm failed with high NOX. He is failing with high HC's (hydrocarbons) which is unburnt fuel. I would say changed plugs, cap, rotor AND wires. I found my coil had a crack in it (had to pull off jeep to see it) so I replaced that too.

-96JeepSpeed- said:

Mine failed to. passed the 15MPH and almost past the 25mph. I need to replace my computer before i try it again.

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Have you checked for recalls? Recall E22 for 96 4.0L XJ's.

A bottle of Lucas fuel treatment some mid grade quality gas and keeping the jeep running before the test has always worked for me. My latest scores
HC co no
max/meas max/meas max/meas

15 123/85 . 73/.35 1015/575

25 103/27 .93/.01 875/199

MJR said:

Have you checked for recalls? Recall E22 for 96 4.0L XJ's.

Click to expand...

I got the recall taken care of. I have manual trans in my jeep and auto computer is still there. My check engine light is on, and the code is for a nutreal safty switch not detected.

High HC and CO is unburned fuel.

Replace cap and rotor.
Check/replace wires.
Check coil (probably fine, but can't hurt.)
Replace spark plugs. Check for deposits on old plugs before buying new ones - see if you need to go one step hotter (which can affect HC and CO.)

Make sure your engine is at operating temperature for retest!

If all of that doesn't work (fuel system deposits tend to cause a lean burn, not a rich burn...) you're likely looking at a catalytic converter.

The cat is a two-stage device. The first stage is "reduction" - conversion of NOx into N2 and O2. The oxygen feeds the second "oxidation" stage of the converter - which oxidises HC and CO into H2O and CO2.

5-90 said:

High HC and CO is unburned fuel.

Replace cap and rotor.
Check/replace wires.
Check coil (probably fine, but can't hurt.)
Replace spark plugs. Check for deposits on old plugs before buying new ones - see if you need to go one step hotter (which can affect HC and CO.)

Make sure your engine is at operating temperature for retest!

If all of that doesn't work (fuel system deposits tend to cause a lean burn, not a rich burn...) you're likely looking at a catalytic converter.

The cat is a two-stage device. The first stage is "reduction" - conversion of NOx into N2 and O2. The oxygen feeds the second "oxidation" stage of the converter - which oxidises HC and CO into H2O and CO2.

Click to expand...

Great explanation! thanks... ill try that and report back after a retest.