jbspencer

Hello,
I'm new to the self repair world and am interested in learning how. That being said, I took this 94' XJ to pass for smog for Los Angeles, CA. Everything passed except the NO (PPM) at 25mph.
15mph: MAX-517 MEAS-322
25mph: MAX-539 MEAS-937

When I asked the guy doing the smog test what general area this issue would take place in to get an idea of where to look first he said he had no clue. Any chance ya'll would know where to look?

Thanks,
Jane

tech

I would start at the EGR valve and if that is working then , Look at the Catalytic Converter .

exasemech

You're jumping in at the deep end with a NOx failure on a Cal vehicle but a few things.

​​​​​​FInd the emission label back on the firewall. It will tell you if It's a California vehicle? Probably but you never know.

The emission label will tell you if it has an EGR system. I don't think 94 will but check the label.

Replacing the catalyst is major money if it's California vehicle but before you get to that point a few things that can increase engine out NOx (and if engine out is high enough a new cat won't fix it anyway)

The EGR system...but don't think it has one but check
Running lean. Check for vacuum leaks,might want to replace O2 sensor if it's been in there a while.

Running hot..is the coolant temp where it should be.

Ignition timing. Not too much to do with that unless things have been hacked.
Compression ratio/combustion chamber deposits. Higher CR will increase NOx.

I don't know if you can even get it in California but I would be inclined to have the tank with fuel with no ethanol when it's tested because of the lean issue assuming your CO level is pretty low.Good luck

Saudade

No EGR on a '94 4.0. Need OP to confirm.

How long did you drive it until you got to the smog test facility? You need a good 20-30 mins of driving (not idling) to get the cat up to full temp.

How are your temps when just driving around? How well does the engine run? Does it shake, low idle, high idle, sluggish? Is your check engine light on?

jbspencer

There is no EGR on this car.

I did not drive it for very long only 1.5 miles. My temps all seem fine, but I'm probably not reading things correctly. No check engine light is on, but also the dash has no working lights on it. The blinkers work and show up. I attached a photo of the dash (car is off) but the top left gauge next to the left blinker light never goes to 210 and the bottom right gauge I feel like never hits 14. If anything I thought maybe everything was low?

I have attached the full Emissions test results.

It has a lot of miles technically 205,8746, but the engine was replaced at some point and I was told the replaced engine was supposedly around 160,000... I don't know how to even check the accuracy. I didn't pay much for the car, just thought it could be a great learning car.

The idling might shake a tiny bit? I am not sure. It is loud, but in the way that my old Chevy truck was loud, and there does seem to be a slight hissing tense noise. There is also a leak coming from the steering fluid pump and coolant leaking... through research, I am thinking maybe the water pump. Not sure if that is accurate. was planning to replace water pump and steering fluid pump/reservoir.

Also found a crack in the vacuum line. The AC does not work. Would love ya'lls opinion. Is this TOO much work needed for a car far too gone?

kindly,
Jane



Found this crack in the vacuum line? could this be contributing?

tech

At 205,8746 miles , does it still have the factory Catalytic Converter ? The 1st thing that goes on the cat is the Nox , the other thing you can try is cleaning the carbon chamber and see if that helps .

exasemech

Thankfully I don't live in California but I looked at the California DMV site. It says that when you sell a vehicle you must give the buyer a "smog" certificate that says the car passed. Did you get one?
if you did it would suggest that the NOx problem is new, and likely not something that happened slowly over time like a catalyst.if you didn't get one that raises other questions.

​​​​​​The test results you posted suggested that the thing is probably running lean and that at least the oxidation function of the catalyst is still good (the low CO ). I couldn't see where the vacuum leak you mentioned was in the picture. I don't know what Cal retest options are but if that thing we're mine I would fix anything resembling a vacuum leak, make sure the thermostat opens at 180, run some combustion chamber cleaner thru it, change the upstream O2 sensor(NGK) , fill it with no ethanol fuel if you can get it, drive it hard for 100 miles, pray...and get it retested.

But that's me,YMMV

jbspencer

Yes! I did get a smog certificate. It passed in December. California is just super strict so even though that should be fine for two years, when you transfer a title they force you to resmog if that last smog hasn't been within 90 days. Thank you all

netdawg

I have a 96 with over 235k and mine (not originally from CA) failed smog this year too. I had to run cataclean in my system to get the measurements JUST BARELY below passing. I wasn't a fan of going with that product but I needed to get it to pass

jbspencer

Since I had a water pump+ power steering pump leak I decided to replace them both. Upon doing so I have found my hoses to be rusty and rust going throughout the lines. SO I will be replacing the hoses, both pumps, the thermostat housing, and the thermostat. I'll be doing a flush of the system and also a decarbonizing of the engine that I've seen in other forums via water/steam method. I ALSO took the advice from above and got a new Co2sensor that I'll be replacing and I'll try the cleaner stuff too mentioned. I'll let ya'll know how it goes.

fingers crossed.

exasemech

And FIX ANY VACUUM LEAKS !

exasemech

Additional thought. Assuming this is a chassis Dyno test make sure tires are inflated to at least the spec.on the door post sticker, another 5+ psi wouldn't be a bad idea.

robsjeep

NOx is created by high combustion chamber temperature. the high temperature often occurs around the exhaust valve. An EGR system is designed to lower that temperature by injecting cool, non combustionable exhaust back into the combustion chamber. that un combustionable added exhaust gas allows cooler temps, so less NOx is produced.
Modern cars can do away with the egr by using a catalyst that in addition to converting HC and CO gasses, can also convert NOx. Modern engine are also controlled in a way to keep those peak temperatures low for the most part so less NOx is created in the first place.

Now the NOx conversion maybe not happening in your catalyst anymore, or you got an engine condition that is causing more NOx production than what a good catalyst can convert.

If your fuel mixture is messed up, like too lean, even on just one cylinder, that can increase NOx. A clogged injector, or intake leak perhaps, or maybe all six are off do to a ***** O2 sensor?

Remember a catalyst works best when really hot, drive the jeep hard, freeway speeds for a good 15 miles or so immediately prior to smog test. Simply idling for 15 minutes may not get it hot enough. However, you are way over on the NOx, dont expect a miracle that will pass you.

Get a read on the spark plugs, are they all good color and uniform? replace if high miles or damaged. check gap of electrode.

Check for intake leaks, make sure all vacuum hoses are good and tight. put a vacuum gage on the i take and make sure it is good, this will help you see general engine condition and if leaky intake or not A spray of flammable aerosol carb cleaner on suspect leak areas when engine is at idle will cause a temporarily engine rpm change as carb cleaner is sucked into through an intake leak.
You can try to test the O2 sensor, or if it is old or un known age, just replace it. they are consumable, replace every 30k to maybe 50 kmiles, Replace BEFORE it goes bad, as a bad sensor can cause damage, rob fuel economy.

If you do replace the catalyst, you should install a new O2 sensor as a matter of course. a ***** or soon to die sensor can damage a new cat. sensors are cheap, cats are pricey! Save your old cat! You may wish to keep the old one on the jeep (hollowed out if clogged) and only use the expensive new catalyst on test days, when it is unlikely to be stolen. A shinny new cat on a jeep is asking to be stolen in a state that refuses to jail criminals, catch and release is only good for fish, not criminals. Calif mandated cats are expensive nowdays. I paid 500 a couple years ago, but prices have increased a lot since then. Dont forget the sales tax that Gov Newsom, and other crooks gets. In many places it is near 10% tax. Youd think smog devices they would make tax exempt? Heck, if you buy a shiny new tesla the state gives you a tax credit, (cause it is good for the earth, right?) but no go for you spending money to clean up your exhaust, the man taxes YOU for that, but the rich tesla buyer, he or she gets a tax credit for that. It is stacked against the average guy, they want to price and regulate you out of your jeep, but you can ride the city bus, while the rich elite drive Teslas subsidized by your taxes.