CA SMOG, HIGH NOx

[Locked98GC]

1 Check ignition timing and timing advance.
2 Check the knock circuit. (Youtube it)
3 No EGR on 94 4.0 Jeeps. (Skip this step)
4 Fuel octane (Is it old gas in the tank? Regular gas is what is needed, not premium.)
5 Check for high intake air temp. (Sucking air from inside engine compartment?)
6 Check for an overheating engine block. When was the last time coolant was changed, thermostat changed, water pump might be going out, radiator getting plugged, general overall condition of the cooling system. Clutch on the fan included. Need the actual temp of the coolant, gauge could be messed up. 1/2 way seems to high, but I have idiot lights, so don't know if that's right.
7 Carbon buildup (Seafoam should have cleared it but might need a second if it was really bad.)
8 Dirty fuel injectors. There are 2 ways dirty injectors can affect NOx without causing increased levels of HC and CO. (1)Spray pattern which can cause hot spots in the cylinders. (2)When only 1 injector is clogged, the rest of the injectors can keep the HC and CO levels within specs, but the lean cylinder's temp increases. (Have you gone through a whole tank of gas with the injection cleaner in it?)

Need a picture of all the used plugs and cylinder they came from. #2 looks OK for the mileage, but #4 looks way to clean.

Need to fix the problem, not put a Bandaid (cooler plugs and snake oils) on it. (well, maybe to get it to pass smog.)

 

[Talyn]

HO engines don't have a knock sensor

For a colder plug try this: NGK ZFR6F-11

 

[jeepsrock]

Sixth Smog Test:
* Stant 180deg Thermostat
* 3 Bottles of ISOHEET with a quarter tank of gas.
* Drove it throughout the week just in case new CAT needed breaking in as mentioned (150miles+)
Failed with similar High Nox but low HC/CO

Seventh Smog Test:
* Put in a pair of 235/75/15 on the rear tires.
Failed with similar High Nox but low HC/CO

8th Smog Test:
* Disconnected Coolant Temp Sensor (smog tech suggestion).
PASSED :huh:


Uploaded with ImageShack.us

The smog tech was helpful and sort of closed one eye since he felt bad i think and let it go through...

I think there is still value in trying to understand why this happened and what can be the causes to correct my lean situation. What happens when the CTS is disconnected ?

Also, should i put back the 190F thermostat in, it runs fairly cold unless i am stopped at a signal ...


Uploaded with ImageShack.us

Feedback is always appreicated !!
Pete

 

[yossarian19]

IIRC a coolant temp sensor is a thermistor, changing its resistance value w/ heat. I don't recall if resistance goes up or down w/ temp, so I'm thinking this through as I type...
It has two wires, 5v power & return. The computer takes that return voltage and knows the engine temp & goes in to closed loop or open loop accordingly. Closed loop, it relies on sensors (o2, mainly) to adjust fuel trim moment to moment. Open loop, it runs off pre-programmed fuel maps.
If you disconnect the CTS, it goes in to pre programmed fuel maps. I think the open loop map is very rich across the board, to prevent fuel starvation & potential damage if anyone just stomps the throttle coming out of the driveway before the engine is warm.

Interesting. I didn't read what kinds of modifications you have done to your jeep, if any, though I suspect that airflow mods (intake or exhaust) have been done without any mods to the fueling end of things.

 

[Talyn]

Resistance increases with temp iirc. You might want to test it using a multimeter in OHM mode. I don't have a chart handy, but there is one floating around here someplace.

What it does is tell the PCM what temp the coolant is at (duh). The PCM then figures timing and fuel based on that value (as well as the other sensors). If the temp sensor were to fault with a resistance under the operating temp value it may be trying to add too much fuel. Un plugging it puts it into open loop mainly relying on the O2 sensors and the fuel and timing look up tables, ignoring the O2 sensors.

I doubt he did enough air flow mods to warrant a change in injectors or fuel pressure.

 

[Ecomike]

Most people would say to put the 190 T-stat back in. I run 180s, but mine are Renix and I live in humid-Hell-Houston, LOL.

Disconnecting the CTS forced the computer to run the engine rich for a few minutes. During that time the new Cat cleaned up the exhaust. Long term that would burn up the Cat(s).

Have you replaced, and or tested the CTS, say at 0 C in ice water, and in boiling water, for the proper resistances?????? If it is, was off say 10-20 degrees, I wonder if that is just enough to nudge you too lean for the NOx limits.

My money is still on the non-OEM aftermarket Ex-Header working too well, and overriding the stock design enough to raise the NOx. I have seen many posts here where they were failing NOx, and had aftermarket tuned Ex-headers.

The CTS resistance drops as the coolant heats up!!!! The CTS sensors are thermistors:

http://www.enercorp.com/temp/Thermistors_comparision.html

If the CTS is good, you might try a tuneable MAP sensor MOD to try and force it just a tad richer for tail pipe inspections, if you can get it past the Californika Gestapo? LOL

 

[jeepsrock]

Well Folks i just got my notice to play the smog game again and i am almost certain the same thing will happen again, how exciting :sure:

For giggles, ill probably take it to get smogged as is and see what happens but i am trying to prepare myself to tackle this problem the quickest and most painless way without spending hundreds like i did last time. The Jeep runs perfectly fine otherwise..

A MAP sensor mod was mentioned to richen the mixture (which i assume is on the leaner side) and thus possibly allow the jeep to pass. It seems that basically the goal is to alter the reference voltage to the MAP sensor (stock 5V) so the resultant output signal is higher or lower. My question is, what does it need to be or how do i fine tune it, the process ?

Thanks,
Pete

 

[mako my day]

You need to smog every year?

 

[BulletMaker]

So in looking at your results, they mirror some of the issues I've had over the years (back when living in CA) that I had with renix XJ's. I know the HO doesn't have the EGR system, however that is usually my go-to when NO tests high on the higher speed tests.

Last time I had to pass one (about 3 years ago IIRC), my problem was caused by vacuum leaks causing the EGR system to not function properly. Also, rather than replacing the cat, I usually tried to get it working before this. A big trick is to run 91 octane fuel when getting your smog done. This really takes care of some of the issues.

 

[jeepsrock]

Smog here in Cali is every other year, so its due unfortunately.

I can definitely try running the initial test with 91 Octane fuel, thanks for the heads up.

Other ideas folks ?

Pete

 

[95XJmatt]

Time for me to hijack the post to shed some light for poor jeeprocks. I am a smog tech who unfortunately owns a 95 xj 4.0 ho and currently pulling my hair out trying to fix my nox problem. It has always tested high nox barely passed the last two years. Smog done 12/18 initially failed nox 1000ppm. I knew going in failure was imminent. Replaced the cracked OEM manifold to cure the major exhaust leak and no major change in nox. Put a new walker "cal cat" direct fit in place of my damaged converter nox has no change. Tune up done with dealer parts runs great decarb services done normally etc etc.

Time to shed light:
Being cheap hurts!
Replacing my denso oxygen sensor with a OEM NTK brand sensor which is designed to switch at a faster rate than most others will. Jeeps are very dependent on a fast o2 sensor as there is nothing to help nox! If a sensor on jeeps is switching from rich to lean over 50 milliseconds its junk... mine is right on the treshold of junk... new sensor and retest with 91 octane tomorrow. I've fixed customers cars nox failures in the past using a better o2 sensor its all about the switch rate... lazy sensors create lots of nox problems.

Being cheap really really hurts!
Aftermarket obd1 cats are junk plain and simple whether its catco or magnaflow or in my case a walker brand.. for all you naysayers ill clue you in.. my local jeep dealer will send me a OEM mopar converter my cost is 900 vs your retail of 1400. There is a reason why the named above cats are under 400 installed... aftermarkets cats are not loaded with enough precious metals to combat a dirty jeep, jeeps are by far the worst in the industry for nox. OEM cats are a little bigger and are loaded up way more than any aftermarkets. I dont like spending money on cars juat for emissions but may have to go the OEM route.....

Until tomorrow one more test... $450 in parts at my cost and hours of labor which retails to cover $1250 at my shop

 

[Dragonslayer]

You never mentioned how far you have to drive to the smog station. If it is nearby, then
maybe the cat hasn't had time to heat up completely. I'm just guessing here.

It helps a lot if the cat is good and hot when testing.

Before getting my cars smog checked I'll drive it on the freeway for a few miles to make
certain that the cat is good and hot. If there is a waiting line when I pull up to the smog
station, I'll drive past and grab a lunch, or run another errand - and then try again later
in order to avoid having to shut off the car for a long time while waiting and lose all that
heat in the cat.

 

[jeepsrock]

Well 95XJMAtt, I look forward to hearing what the results of your smog inspection today are, I am keeping my fingers crossed for you ? No doubt that component brands make a difference, but i am not entirely convinced that good brand components which have guidelines to meet would cause a failing situation, but heck i could be wrong.

Dragonslayer, I always give my Jeep a freeway trip before taking it to the smog place and if i have to wait a few mins i keep it running, so i doubt that's the issue.

I definitely think i need to check my vacuum lines, its one thing i cant say i've checked entirely, i just wish there was a systematic way of checking the pressure and seeing if there is a leak or not instead of hunting !!

Pete

 

[blondejoncherokee]

Im in California too. Before I smog my heep (every 2 years) I replace:
sea foam in intake, gas tank and crank case(maybe half quart of DEXIII in the oil too)
then add some acetone then drive it for a week

then do:
Plugs
cap and rotor
02 sensor
fuel filter
check all manifold bolts/look for exhaust leaks
test all sensors
more than likely replace a sort of bad TPS
check all vacuum lines
adjust TV cable for fun
put about 2 pints of acetone in the gas tank
change oil(due to the sea foaming)
check fuel pressure
make sure cat is good(if not replace)
clean ALL grounds
clean all electrical connections
clean throttle body
flush cooling system if it hasn't been done in a while




its an old renix. it only gets like 3000 miles a year max put on it, some years 2000 some years 5000 . I figure a full tune up every 2 years is totally fair. I actually do that all almost every year. Thing always runs great and starts right up.


It always passes with flying colors. of course, this will be my first year smogging with 36s and a pacesetter header so I am already planning to have to throw a stock header and some 35s on in case it doesn't pass the first time, but I am sure it will pass.

Not sure if it makes a difference but mine also has a bored out TB, ford 19lb injectors, and a slightly moved over CPS.

 

[95XJmatt]

Okay here we go boys and girls its time.... no snake oils garbage intake cleaners lucky chicken bones just installing correct parts. Just for kicks since im a smog tech ran jeep in dyno failed nox 300ppm 15mph and 1000ppm 25mph after the walker cat had 100 miles. Put in the new oem ntk oxygen sensor drove the jeep for 20 miles modestly not superheating the cat as many suggest then re smogged to find nox now 4ppm 15mph and 84ppm 25mph hahahaha chew on that!
1995 xj 4.0
200000 miles original engine
Blew damn new zeros on the smog check
No tricks or gimmicks just fixing cars is what i do

 

[95XJmatt]

Oh also forgot to post lambda calculation on both asm speeds came out to .9997 doesnt get much closer to stoich than that.

 

[blondejoncherokee]

NTk is only 6$ more than BOSCH on rock auto, is it really that much better?

 

[95XJmatt]

Buy from the dealer only for your ntk sensor the mopar part number doesnt match the one cataloged by most part stores... bosch has to be the WORST sensor you can put jn jeeps i only install bosch on euro cars..

 

[jeepsrock]

95XJMatt, I think that's great that you passed, wonderful news and a headache avoided, hahah.

I just spent a good few hours inspecting the Vacuum Lines with a Vac Gauge and making sure everything holds pressure well enough. I will definitely give the manifold a check as well, so far so good !!

I understand that the after market NTK sensor i purchased may not be the same as the Jeep dealer one but how do i verify my changes and diagnostics ? For example can i monitor the MAP/O2 sensors voltage to see if i am indeed running lean and see if my efforts are helping ?

Thanks,
Pete

 

[95XJmatt]

I know and honestly in the years of auto and smog repair ice never seen a jeep with such low emissions i am stoked should be good for years of smogs. The best way and only proper way to check an oxygen sensor is with a digital multimeter and lab scope. Multineter will record high low and average to tell you if its biasd rich/lean by how close to 450millivolts. The scope is necessary to monitor the switch ratio fron rich to lean. Faster switch ratio and tightness to stoich is a must to light the cat off just right. All honesty theres really not alot to these h.o. engines as long as the basics are covered.