hello all, i am new to the forum and hope this is in the right section if not i apoligize. ive failed my smog check 4xs already for ONLY nox being slightly high. i havent update my jeep info yet but its a 95 HO 6cyl. all stock cherokee with 71,000 miles on it. in attempt to fix nox ive done: new spark plugs-new map sensor-new ect sensor-new o2 sensor(denso)-new air filter-ran berrymans b12 chem through tank-changed ALL vacuum hoses-ccv valve is clear no clogs. test results are attached as well as LAMBDA calculations. any help is greatly appreciated!

 

Sounds like it's running lean. EGR system?

http://www.smogtips.com/failed-high-...rous-oxide.cfm

Max

 

my year xj doesnt have an egr system. it doesnt overheat at all and runs great. it does have some carbon build up in the combustion chambers and im currently running my 2nd tank of berrymans b12 fuel system cleaner in it and possibly inject water mist into intake to help clean out chambers. i can replace the CAT but id prefer to make sure all is well before masking a possible problem.

 

anyone else have any thoughts? would a CAT be less efficient at 71,000 miles or just less efficient from age?

 

I have been helped by adding a few gallons of E85 to correct my emmisions, just before going to the test station.
By using a few gallons of E85 every second month have helped me to keep
my fuel system ok.

 

Had the same battle.https://www.cherokeeforum.com/f2/ano...g-fail-186665/
After spending $500 plus,I won.Combustion temps must be as low as possible when testing.185 stat will help and let engine cool down before test.
Crankcase blow by into intake system will also increase NOx.
Good luck.

 

i currently have a 180 deg thermostat in... my temp gauge is ALWAYS at 190 and NEVER goes higher. i have also wired the electric fan to be on during the test, which has helped but not enough. my NOX is only slightly high and the rest of test results are good! if anyone knows about LAMBDA its results say im running pretty much close to perfect. out of all this attempt to lower nox the only thing ive noticed to be bad was A LOT of carbon build up in my chambers. i know this highly contributes to NOX so im running my 2nd tank of gas with berrymans b12 total fuel system clean along with chevron gas. my first tank with berrymans helped clean out some but theres still some slightly carbon inside chambers. hopefully 2nd treatment will help even more. im gonna also try water injection to help even more clear things up. other than carbon build up my last shot is NOT a bad CAT but replace a CAT that just isnt fully efficient to do its job. according to test results CAT is doing its job. i will later use my infrared temp gun to check in/out temps on cat... will report back. thanks ALL.....

 

ok if i did it correctly from the same distance each measurement..
the front inlet pipe of CAT was 218 degrees f and the rear outlet was 256 degrees f. i revved it a bit before the reading but was in a rush. gonna try 1 more time in a bit after an errand run and report back.. from the previous reading, seems like cat is going out although it looks in good condition and doesnt rattle or anything. also my HCs COs are good and i though if a CAT was failing ALL numbers would be high???...hmm.

 

having the same nox issues on my 93 xj..

first run:

co2% = 14.9
02% = 0.0

hc 15 mph = 33 ppm
hc 25 mph = 27 ppm

co% 15 mph = 0.05
co% 25 mph = 0.03

nox 15 mph = 781 ppm
nox 25 mph = 535 ppm

so i replaced the catalytic converter with a magnaflow carb aproved model, map sensor, and fuel pressure regulator

second run:

co2% = 14.7
02% = 0.0

hc 15 mph = 3 ppm
hc 25 mph = 2 ppm

co% 15 mph = 0.00
co% 25 mph = 0.00

nox 15 mph = 1147 ppm
nox 25 mph = 534 ppm

so i changed the 02 sensor, ntk brand

third run:

co2% = 15.1 & 15.0
02% = 0.0

hc 15 mph = 13 ppm
hc 25 mph = 14 ppm

co% 15 mph = 0.02
co% 25 mph = 0.02

nox 15 mph = 1069 ppm
nox 25 mph = 981 ppm


added 100 octane gas, oil change, plugged fuel pressure regulator vacuum to make it run rich

4th run:

co2% = 14.7
02% = 0.0

hc 15 mph = 11 ppm
hc 25 mph = 8 ppm

co% 15 mph = 0.01
co% 25 mph = 0.01

nox 15 mph = 1226 ppm
nox 25 mph = 1016 ppm

going crazy over this. so i haven't done anything with it in about 2 weeks, started reading into fixes again last night. this morning i fire it up and look for exhaust and vacuum leaks. used brake parts cleaner at vacuum connections, no change in idle. haven't checked the manifold yet, but I did find a small hole at the weld of the new catalytic converter to the down pipe. this is directly in front of the cat, past the 02 sensor. the muffler shop is going to fix the weld today, but I've lost hope in this being an easy fix. what else can I do? I've yet to check fuel pressure but the Jeep runs as smooth as ever. smooth idle.

please help.

edit:

i sea foamed the jeep 2 years ago. 2 cans total through the intake, crank, and fuel tank. it's at a 3" lift on 31s with auto lockers and about 500 lbs of armor, so it's got a little more strain on it than stock. i've probably put on less than 18k miles in the past 2 years.

 

high Nox is also caused by carbon build up in the combustion chambers. you can check by removing plug #1 or #2 and flash a bright light inside and take a peek. if you do find it to be carboned up use a combustion chamber cleaning product. the ones that attach to the fuel rail or vaccum line. CRC makes a good one and so does berrymans b12 chemtool. what kind of plugs are you running? ive failed 4xs already also. my last option is combustion chamber cleaner or CAT.. im looking to find the problem and not mask it though. also ive heard of bigger tires causing higher nox due to more stress on motor turning them. and the 500lb armor definetly cant be good either..........

 

checked in/out temps on cat again and there only 60-65 degrees different.. looks like cat is not working to well.. also when testing cat temps do i need to check while revving rpms? i had it fully warmed up and drove it for a bit then measured the temps during idle...

 

anyone have any thoughts??

 

just ran the jeep for 30 mins highway and took temp at CAT. inlet was 270 deg and oulet was 281 deg... ive checked the temps 3xs and they have all been 30-50 degrees apart. i dont know if its normal temperature but if anyone else can see something im not PLEASE help

 

It should be about 100* hotter behind the cat. Sounds like the cat is not working too well.

Max

 

Changed out old cat and installed new magnaflow and NOX went up even higher.. ive replaced every thing on the list for high nox causes.. im puzzled. Can anyone please direct me on what I should try next?