yet another high NOx smog issue

Sorry if this is a bit long, but I want to include all pertinent info.
For the last month, I've been attempting to get the new-to-me renix to pass smog. as of this afternoon, she's failed three times now.
First test nothing was really done in preparation(cap/rotor/wires/plugs were recently changed before i bought it). all numbers were well under max EXCEPT nox-which was around 1100 at both 15 & 25mph(max is 714/616).

Before the second test, I decarbonized it with the water spray method, changed the oil, and just kind of went over everything. that test failed with almost identical numbers, except the NOx went down to 975 @ 15, and 977 @ 25.

Yesterday I changed the plugs to one heat range colder, and installed a new egr valve as I discovered the transducer diaphragm was totally shot. I also changed the o2 sensor and the coolant temp sensor just because they were clearly old.
Went down again this afternoon, and failed once again. Now nox was back up to around 1074 @ both 15 & 25. the other numbers improved slightly, still around "average".
I'm a bit shocked that going from a nonfunctional egr to a new one(did test it, it is good) did nothing at all to improve the results.

the jeep runs great, has good power, good mpg, doesn't overheat, etc.
I drove around this evening with a vacuum gauge on the dash hooked to the egr line AFTER the transducer to verify it was getting vacuum to the valve when it's supposed to. It does seem to be working properly, as I see anywhere from 10" of vacuum to full engine vacuum at the valve under mild acceleration and slightly loaded cruising depending on throttle position.
I have done the lambda calculations and I'm right at 1.002 @ 15, and exactly 1.0 @ 25. This tells me that the air/fuel control and combustion is perfect.
The smog guy swears it has to be the cat, and it is an aftermarket one that looks to have been replaced a long time ago. Also, he and I agree that it looks kinda small?

I don't want to waste money on cat replacement unless I'm very sure that's the solution.
Also, I'm not sure if this matters, but I am running the high altitude cps. I'm wondering firstly- would a dead/dying cat affect the nox in the range of 900ppm? And secondly, does anyone think the +5-6 deg of advanced base timing would be enough to screw up the nox to this degree?
Thanks for any input...

I went through this a few months ago with the IM-240 program. My Co and HC readings were about half the prescribed limits for my state. The reading for NOX was just over the fail point. A new CAT brought a dramatic reduction to all the measured pollutants.

If only NOX is high and all other measurables are good, more than likely you're jeep is suffering from excessive cumbustion temps. It took me 4 try's to solve the problem.

Since we can't tinker with the timing, The only thing that worked was a 180* thermostat and spark plugs that were 2 heat ranges lower than stock. After these mods I passed with flying colors.

You may find this thread helpful. Good luck.

http://www.naxja.org/forum/showthread.php?t=1083101&highlight=Smog

My NOx was high and all other measurables were good on the first test. I passed on the second attempt after sealing some exhaust leaks and borrowing stock tires and wheels from another rig. (I was running 32s on 3.55:1 gearing. That is now being remedied.)

Mine was from a crack in manifold that i couldn't hear. I used Sea Foam an i found it, this was after i bought a new cat and had it installed(failed).Sea foam it and them let it sit a few minutes, then re start it.I used the wife to start it so i could see every part of the manifold. After replacing it i pass with flying colors. Start out with the cheap easy stuff, Sea Foam.

I should also mention that I'm running 31's on 3.55's. I had a small leak at the donut in the down pipe connection, but I tightened it and it *seems* fine.
I'm going to change that donut gasket, and inspect the exhaust with seafoam.
I don't want to dump the money into the cat + another $40 for retest, until I'm sure.
Does anyone know if the renix years use a 3-way cat? I had always heard they didn't, and all the nox control was via egr, and that the cat changed for '91-up.
Hypoid, your situation sounds similar to mine-is your's a renix?

Yes, a 1990.

I had someone else look at the emissions report. The CAT was his first thought, and the only thing I changed after the failed test.

I will say, if you are planning on the Sea Foam treatment, do it before changing the CAT. At least when you do change it, you won't have any Sea Foam spooge plugging up a perfectly good CAT.

ok, that sounds like a plan. I was concerned that a renix cat wouldn't do anything for nox reduction. it sounds like that isn't the case after all.
any idea what brand converter was installed?

Hypoid said:

Yes, a 1990.

I had someone else look at the emissions report. The CAT was his first thought, and the only thing I changed after the failed test.

I will say, if you are planning on the Sea Foam treatment, do it before changing the CAT. At least when you do change it, you won't have any Sea Foam spooge plugging up a perfectly good CAT.

Click to expand...

Hellbent said:

ok, that sounds like a plan. I was concerned that a renix cat wouldn't do anything for nox reduction. it sounds like that isn't the case after all.
any idea what brand converter was installed?

Click to expand...

Have you ever seen this link? Couldn't hurt to do 1 through 5, and maybe 27, as these grounds/connections affect what the ECU sees from the sensors.



http://www.cherokeeforum.com/f51/cruiser54s-mostly-renix-tips-153657/

I've done all the "renix things", every one, except eliminating the c101. I plan to do that at some point in the future when I have the time. For now, all the goo is cleaned out and I used contact enhancer on reassembly. :cheers:

cruiser54 said:

Have you ever seen this link? Couldn't hurt to do 1 through 5, and maybe 27, as these grounds/connections affect what the ECU sees from the sensors.



http://www.cherokeeforum.com/f51/cruiser54s-mostly-renix-tips-153657/

Click to expand...

Hellbent said:

I've done all the "renix things", every one, except eliminating the c101. I plan to do that at some point in the future when I have the time. For now, all the goo is cleaned out and I used contact enhancer on reassembly. :cheers:

Click to expand...

Maybe it's time......

now for an update...

It finally passed, and with great numbers.
First test-passed around average on hc/co, failed with NOx around 1100 @ both 15 & 25.
second test-decarbonized with cold water & changed oil(was due anyway). checked all hoses, manifold bolts, etc. hc/co passed around the same numbers, NOx failed again around 975.
third test-changed plugs to one heat range colder, new egr valve(diaphragm was toast), new o2 sensor, new coolant temp sensor. failed again. hc/co were slightly lower, and NOx went UP to around 1075.
lamda calculator showed pretty much perfect air/fuel at both speeds-1.002 & 1.0 I believe it was.

Did a bunch of research, checked everything, verified egr system was indeed working correctly now. smog guy had remarked that the cat "seemed kinda small" for the application, and it was clearly aftermarket and old.
bought a new magnaflow cat thursday, welded it on. The new one had a body that was 3/4" wider and taller, and 4" longer than the old one.
Put about 50 miles on it after the recommended break in procedure.
Took it in this morning, passed with ridiculous numbers on the dyno test.
15mph: hc 12ppm / co 0.0 / NOx 31 ppm
25mph: hc 7 ppm / co 0.0 / NOx 3(yes just 3)ppm
lamba calc shows .9998 and 1.0. doesn't get much better than that.

for future searchers: this is an 200k aw4 renix, 3.55's with heavy ass red label 31's, 4 hole ford injectors, bored tb, magnaflow 2.5" cat back, and high altitude(+5deg) cps.

Hypoid said:

I had someone else look at the emissions report. The CAT was his first thought, and the only thing I changed after the failed test.

Click to expand...

I left out that we used an infrared thermometer to check exhaust temps before and after the CAT. With the engine at operating temp, I read (at most) a 10 to 20 degree rise in tailpipe temperature. After installing the new CAT, I had a 60 degree rise in less than 5 minutes running.

I was talking to someone else about verifying his CAT and remembered this thread.

I was going to check the inlet, outlet, and body temps of the cat. Buuuuuuut I can't find my infrared thermometer...dammit.

Hellbent said:

I was going to check the inlet, outlet, and body temps of the cat. Buuuuuuut I can't find my infrared thermometer...dammit.

Click to expand...

Doesn't that just chap your hide?

I went through the same thing last month, but my nox reading wasn't as high. I tested three times, each time putting more e85 in the tank, each time the nox reading improved. The final mix that got me passed just under the max reading was 2 gal of e85 and 2 gal of premium total in the tank.

My '88 failed twice as well. Put a new Walker CAT on it Saturday. Just got back from smog test. NO mesaured at 0 (Zero!)!!

I have a brand new walker cat(among other things) NOX is still around 1000.

Great to hear that you got it figured out. I'm sort of surprised that the cat made that much different. I feel like I should add a downstream o2 sensor so that I can be sure mine is working correctly. I've got a Renix system and 703 injectors, so it runs super rich for the 5-8 seconds it takes the o2 to kick in. It probably heats up the cat extra quick