Failed emissions test, extremely high HC

Hello everyone,

I have found the various threads on people's experience with emissions failure and repairs a good source of information.
(in fact I've had such great experiences with that I am finally going to join after I finish this post)

So I thought I'd post my experience with mine. My hydrocarbon #s seem to be much higher than other failures I read about:

IDLE - FAIL
HC ppm 1123 (limit: 220)
CO% 1.62 (limit: 1.20)
CO2% 10.0
O2% 5.6

HIGH IDLE - FAIL
HC ppm 811 (limit: 220)
cO% 1.07 (limit: 1.20)
CO2% 11.7
O2% 3.3

I have a rusty 1995 daily driver -- AX-15/NP231/2.5" OME/31" KM2. No metal floors but great interior from the junkyard (tan w/ "wood" dash). Windows broken open and no doors in the summer. The theme of this Jeep is not spending money and looking great doing it.

The exhaust has rusted out quiet badly. Exhaust manifold is badly cracked but hasn't gotten worse since I swapped out a sheared driver side engine mount a couple years ago. The downpipe is badly ventilated and was recently welded to the cat when that interface failed. The cat seems to flow but is probably burned out inside. The muffler and cat-back I was recently forced to replace with an identical Flowmaster 40 and a generic Walker pipe. I last passed emissions in 2010 with a cracked header so I'm not too worried about that. I am going to try and "booger" weld it like I did with the downpipe. I do want to eventually replace the downpipe and cat. But for now I want to see how far I can get the #'s down with just a tune up.

The engine pops frequently on decel and misses occasionally in steady state. Not enough that I think it's a burned valve. But I will look for that.

My plan for the weekend:

- I do think the o2 sensor is shot 10x over living in these rich conditions. So that's getting replaced with a Bosch 15704 sensor I already have

- Replace the plugs and factory gap

[those 2 should do it but while I'm at it..]

- Compression test

- Verify air charge temp sensor with ohmmeter

- Inspect the wires, rotor and cap. Might swap them with my other jeep only as a test

- Check for lack of RPM drop while turning each cylinder spark off

- Check EGR and PCV operation

- Finally, drain the oil/gas mix and replace with straight oil before I lose a bearing

I will post my new numbers once I re-test.

Suggestions, criticism, etc. are appreciated!

Thank you

- I tried to wrench out the o2 sensor with PB blaster but if I put any more force into it, the downpipe will break off about a foot downstream. I might as well cut out the downpipe and replace it. I would need a new cat too as I don't think I can weld to this one anymore. I'll try again tomorrow after a longer PB soak time and then put it on the back burner pending outcome of next emissions test.

- All six plugs were ash fouled with thick deposits, two with additional black crud between the electrodes.. Bosch platinums replaced with copper Autolites @ .035"

- Compression test: warm, CPS unplugged, WOT, 10 cranks
#1 140
#2 145
#3 145
#4 150
#5 140
#6 155

- The MAT/IAT/ACT/whatever sensor measured 6,650 ohms. ECT should be same so using this thread I should be around 2500 ohms for a 80* ambient temp, probably closer to 1600 ohms with heat soak. But probably still within the purview of fuel trims. If not I will map out it's current characteristics and shunt it.

- Evidence of condensation in old oil. XJ was sitting all winter waiting for a new rear end so not surprised. Haven't lost any coolant.

I'm going to try and get retested Monday or Tuesday. I think the HC will be much closer to the State limit now. Might get lucky and pass without additional changes.

Also in my searches I have discovered bimmerjeep and have been reading thru his journey.. It's riveting! Nobody ruin the ending for me please, I'm almost done

With the misfire gone my HC #'s improved dramatically:

IDLE - PASS
HC ppm 118 (limit: 220)
CO% 0.70 (limit: 1.20)
CO2% 12.3
O2% 3.4

HIGH IDLE - FAIL
HC ppm 56 (limit: 220)
CO% 1.97 (limit: 1.20)
CO2% 13.8
O2% 0.4

But my CO went over the limit on the high idle test. And I really don't feel like shelling out cash for a new cat...

Next steps:

- The engine burns a little bit of oil. I'm going to clean the gunk out of the intake, TB and PCV. Then I'm going to do a can of Seafoam. Then replace the current oil (mostly 10W-30 with a dash of 5W-30) with some thicker Rotella T6 I have sitting around.

- I am also going to attempt to wrap what's left of the downpipe with Permatex 80334 and cure it with a torch so it doesn't blow out (more for my own health than the car's)

- I'm going to clamp my wbo2 onto the tailpipe and see what the AFR looks like at idle and high idle. If it's not stoich at high idle I will shunt the MAT so it has the correct impedance at appropriate temp. If it's still not stoich I will replace the damn o2 sensor.

If that doesn't do it then I may replace the cat. Or just add alcohol-based fuel to the tank for showtime.

Any other ideas?

I usually do a full tune up, clean grounds and all sensor connections, , and replace the o2, make sure you have no exhaust manifold leaks at the head and the collector.

I also put around 2- pints of acetone the week or two before, then a few days before add another pint of acetone, and 91 octane.