Failed Emissions 3 times HELP!

OK so this is getting to be very much a pain da rear, ya know? I have a 95 4.0L AX15 4x4 156k miles on it. Bought it 45 days ago from a dealer so I have no history on it.

The truck is failing in NOx, but it ain't doin too hot in the other areas (HC's and CO) either. The WI test puts the truck on a dyno and runs it through a little cycle of varying speeds. My emissions spike when accelerating. At cruise the emissions look pretty good, but all 3 spike when the gas is hit.

So far I've checked all the vacuum connections, found some loose, broken or missing and fixed them. I've also done this:

Before 1st test:
-new plugs, wires, cap & rotor (orignal plugs were found to be running pretty lean)
-180* thermostat and rad flush + new heater valve
-ran 1 bottle of lucas fuel system cleaner through truck

Result->>>Failed NOX and HC's

Before 2nd test:
-Fixed a bunch of vacuum lines
-replaced rusted up clogged fuel filter
-installed FM 40 series muffler w/rusty's tailpipe

Result->>>Failed NOX even higher

Before 3rd test:
-new banks knock off header from APN to replace cracked header
-cleaned out all the carbon deposits (really bad) from intake manifold and intake ports on head. Found lower injector o-rings to be packed with carbon and gunk and I cleaned all that out
-Replaced Fuel Pressure Regulator cause it was allowing fuel pressure to fluctuate too much

Result->>>Failed NOX even higher than 2nd time

I haven't taken it to a mechanic yet as I'm not super rich. I know they would want $700+ to fix whatever it is that is wrong.

Add'l info:
-idle wanders up and down very slightly at idle when cold
-O2 sensor and cat are original as far as I know.
-no codes for anything
-Jeep generally runs well and gets good mileage (20ish mpg)
-haven't checked the MAP or any of the other sensors-figured if they were bad I woulda gotta code
-Even for having a FM 40 it seems quiet...too quiet...

Can anyone help me with this? I'm not a big fan of just replacing everything and seeing if it works. Only reason I replaced the stuff above was cause it needed it. If anyone has any brilliant ideas I'm game...

thanks!

Nick

The cat's original? Maybe it's time for a new one...

i have about the same jeep as you. i would replace the cat. mine looks bad and most likely would not pass. thats the first thing. i would also replace the 02 and any thing that has to do with the exaust. then get it checked again.

i assume they are nice about it and don't charge you if it fails?

Correct thermostat - 195
Change O2 sensor
At that mileage...I would also change the cat.
Get it hot before the test, drive it at least 15 min.

Rev

failing on NOx is a result of high cylinder temperature. mine did it too. egr valve or egr solenoid is bad. mine was the solenoid.

90xj06 said:

failing on NOx is a result of high cylinder temperature. mine did it too. egr valve or egr solenoid is bad. mine was the solenoid.

Click to expand...

he's not got an EGR system.
Deleted in 91.
I second the cat movement.

Yeah the high NOx failure does have to do with cylinder temps. Could be a problem with firing in one or more cylinders resulting in an incomplete and lean burn with the excess fuel dumping into the exhaust.

I'm pulling the plugs at lunch today and going to see if they tell a story.

I'll keep this post up to date and let people know what resolves this in case anyone else has the same problem.

I hesitate to replace the cat since the other emissions are in spec. We shall see...

thanks for the ideas guys!

High NOx emissions occur either because the cat has gone bad (likely if you still have the original), or combustion temperatures are too high (lean condition).
I don't think any of your sensors are bad 'cause the engine runs well. A bad O2 sensor usually causes a rich condition and poor gas mileage. You don't have either so your upstream O2 sensor is probably good.
Check the color of the deposits on the center electrode of your plugs. If they're white, the engine's running too lean. If that's the case, I think the most likely reason is clogged injectors especially if they're 156k miles old. A new set of 21lb injectors should take care of that problem, and replace the cat if it's the factory original with a 2.5" Carsound high-flow unit.

Can a Dealer legally sell a car that don't pass emissions? In Ohio they can't it must be smogged first in counties where testing is required.

I agree with the cloofgged injectors. I had a high Nox issue awhile back. Search with my username and NOX to find my posts. You can get your injestors cleaned for about $15 a piece, but I did mine in an ultrasonic bath.

I also used www.passsmog.com High Nox formula. All I can say is that I passed.

O2 sensor got me to pass the high NOx I had. It was easy...... dump an ounce or 2 of acetone to 10 gallons and it even lowers the HC's a bit! i did this in march. worked great.

I pulled the plugs and the motor is definitely running lean. The weird thing is though the base of the spark plugs were a bit black indicating excess fuel at high throttle.

If anyone wants to just give me $500 so I can go buy all the new parts and slap it back together I'll go do that. hahaha that would be much easier. I'll call the dealer and see what they want for cleaning the injectors.

I'll pull my O2 sensor tonight and see how it looks. A thick carbon coating can delay response time and different colorations can tell you different things about it. Similar to a spark plug...

oh yeah-another piece to the puzzle-which makes sense I suppose-is that at the instances where the motor was outputting too much pollution (when accelerating), the A/F ratio was slightly rich.

the saga continues...

thanks all...

I had a tough time with high NOX a while back and swapped out everything I could and then it just kept testing higher. The one thing I missed was the o2 sensor, after I replaced that it passed with flying colors!

POSXJGuy are you saying you replaced the O2 sensor, or just that you put some acetone in the gas?

I need to fix the root problem here cause my truck is running lean and that ain't good. I'm trying to stay away from miracle bottles...of course if it's just a good fuel injector cleaner, that would be cool...

ukdkbr said:

I had a tough time with high NOX a while back and swapped out everything I could and then it just kept testing higher. The one thing I missed was the o2 sensor, after I replaced that it passed with flying colors!

Click to expand...

Souds similar to my problem...Maybe 'tis the answer. I was perplexed that as I fixed MORE stuff my NOx kept going up!!! :sure:

they really got rid of egr valves? where have i been the 80's o wait ya i was. the newest car i got is 1990.

Yeah we lucked out on the later XJ's LOL!

Gator4x said:

POSXJGuy are you saying you replaced the O2 sensor, or just that you put some acetone in the gas?

I need to fix the root problem here cause my truck is running lean and that ain't good. I'm trying to stay away from miracle bottles...of course if it's just a good fuel injector cleaner, that would be cool...

Click to expand...

Hey Gator, i replaced the O2 sensor and it lowered my NOx and as a bonus i added some acetone (2oz to 10 gallons of 87) and it brought the hc's down as well.

The O2 sensor will directly affect the NOx though. Acetone was just an experiment i wanted to do for the HC's, it worked.

Acetone cleans out the fuel system somehow and even makes it run better. My xj got quieter as well for some reason. The mechanic said whatever I did it worked. O2 does directly affect the lean condition you are referring to though. Less gas iinjected to cylinders due to bad reading of old ass O2 sensor made me fail with high NOx. After installing the new sensor I was back to normal, engine even ran a little cooler after and the lower temps lowered NOX readings.

freakin money. I wanted to take a sledge to the test techs when they kept tellin my the NOX went up again. I know it's not their fault, but gosh darn this emissions stuff is agravating!

make a friend and cough cough cheat.