CA SMOG, HIGH NOx

[2WDNICK]

I just replaced my muffler, I have several different leaks at the clamps and adapters after the Cat, would that make much of a difference passing smog?

 

[jeepsrock]

This sounds all too familiar sadly, and from the beginning I wanted to find a solution as well. I am sure if you read this thread you'll see i too had increased numbers with the new cat, several bottles of HEET did nothing, New O2, and my Jeep runs at the proper temperature as well :/

The only thing that ive been able to do in last few times to get it to pass was unplug the Temp sensor connector on the T-Stat Housing.

I would love for you to make a break through here

Pete

 

[blondejoncherokee]

you need to weld up those exhaust leaks. the clamps don't fully seal. Depends on what part of smog, box, Hydro carbons, etc. get a pre smog and then diagnose any point of failure,

 

[luv2whl]

Read through all the posts and a great help.

I have a 1984 CJ, CA approved Mopar MPI, 4.0 head, and CA approved Borla header. I have had this set up for 15 years, although recently rebuilt.

When lived in the Bay Area if failed smog due to high NOX. Putting on small tires solved the problems.

Moved to the foothills and passed the basic test (No dyno) easily. Just moved and now need to do dyno and failed due to high NOX. HC and CO about zero.

Since first test I have:
- changed tires from 37s to 28s - reduced NOX from 2800 ppm to 1400, failed

Then changed:
- thermo from 190 to 160
- reduced timing from 14 btdc to 8
- replaced CAT with ne Magnaflow
- installed manual fuel pressure regulator on rail, set at max, but not tested
- installed cooler plugs recommended by Hesco.

Still fail NOX, readings now a 1,4000

I did calculations with my manual trannie, tire size and axle ratio. With the 28" tires and effectively a manual 3 speed (4 speed with granny), I am running at about 1450 rpm at both the 15 and 25 mph tests.

How much is NOX dependent on RPM, and lugging engine??

Based on my calcs, if I install 33s off my sons truck, the test could be run at about 2,200 rpm at both speeds. Seems that allows the motor to run in its power band, and those reduce load and temps, and NOX.

Help

 

[blondejoncherokee]

exhaust leaks? try adding some alcohol since it burns cooler. I used a ton of acetone and HEET in addition to a ton of other things - does it have an EGR?

o2 sensor new ? Consider a new o2.

Did you put a new Cam in the new rebuild or anything like that?

take it in cold, then let it sit a while before they touch it so it cools down again.

 

[jeepsrock]

Well I know its been several years since my original posting but the time is here again and I know that I will likely fail on the same account, high NOX.

There is tons of good info here and i can start replacing parts again as i tried the last few times (and i will try again if i must) or i can take it to someone who's familiar with these problems.

Does anyone know of someone experienced and trustworthy in the Los Angeles/San Fernando Valley Cali area ?

Pete

 

[bchulett]

I've kept every smog test report since I bought my Jeep Cherokee in 1991 and started this ritual in 1997.

I can tell you this.. one year they lowered the thresholds.

 

[jdzumwalt]

I had issue with high nox, replaced the 02 sensor with a OEM ntk sensor problem solved

I tried everything, cleaned the intake, replaced fuel filter, added techcron ect. New sensor from jeep fixed it dropped nox from 1000 to 20. No joke. Also jeep runs much smoother and runs cooler on the radiator temp.

 

[Ecomike]

I had issue with high nox, replaced the 02 sensor with a OEM ntk sensor problem solved

I tried everything, cleaned the intake, replaced fuel filter, added techcron ect. New sensor from jeep fixed it dropped nox from 1000 to 20. No joke. Also jeep runs much smoother and runs cooler on the radiator temp.

What year jeep?

 

[zouch!]

i'm also having trouble getting my '94 to pass Calif smog
mine: '94 XJ Sport, 4.0L, AW4, 30" BFG ATs @ 32PSI (stock 3.55 gears)

problem is only for high NOx; high at both high and low speed. all other numbers look very good, far below average.
[i didn't figure out how to post a pic, but here are the numbers.]
CO2 is 14.7
O2 is 0.0.
HC is around single digits
CO is 0.01.

but, NOx:
15MPH Max: 517, measured: 1379
25MPH Max: 539, measured: 1266


O2 sensor is a new NTK from the dealer, with about 250 miles on it.
Cat is a new Magnaflow, with about 800 miles on it.
spark plugs are new factory recommended Champions gapped at spec (.035"). these replaced a set of Autolite 985s that came out completely white/grey after ~16K miles.
new water pump (Flow Kooler, which seemed to work better at low speeds than the Hesco it replaced.)
new factory fan clutch.
these things (and running 92 octane instead of 87) brought my NOx down only about 100 points from the previous test.

other factors:
Borla header, with the O2 sensor moved down to the headpipe to read all 6 cylinders instead of just 3.
matched set of stock injectors (from Lindertech) tested fine on an O'scope.
new CSF brass/copper radiator
recent TPS (factory)
recent Idle Air Solenoid (factory part) and a good throttle body cleaning
recent coolant temp sensor (factory)
fuel pressure tested within spec.

- it does seem that it's always wanted to get hot easier than i think it should; hot enough that it'll engage the auxiliary/electric fan during the test even on a cool day. (the only time this thing didn't seem to run hot was when i had a Griffin radiator in it, but that thing only lasted about 3 years before it cracked a leak.)
- Catalytic convertors on this thing get chewed up rather quickly; cheap ones are ruined in just a few thousand miles, and the new one is already purple and blue from the heat.


i'm open to suggestions as to what the problem might be and what to check next; i even resorted to trying some of that Guaranteed to Pass junk and it actually made all the numbers worse. (i changed the O2 sensor after that.)

 

[bchulett]

I just got my 1991 tested ... 181,000 miles. Stock.. I'm on the threshold.

15 mph... HC MAX... HC AVG ... HC MEAS... NO MAX... NO AVG... NO MEAS...
...................86.............26................86.............711..............254..............547

25 mph... HC MAX... HC AVG ... HC MEAS... NO MAX... NO AVG... NO MEAS...
..................103............22................58.............613.............173..............500

It appears I'll need to do some work to get it to pass in 2018...

.

 

[zouch!]

@bchulett:

where are you located?
with numbers like that, you would have failed already in one of the more strict regions.

after changing out my Borla header for a Banks (because Auto Electric and Fuel found some leaks in the collector on a smoke test), i've now gotten my numbers from the previous post down to where i'm only about double the limit here on NOx for my '94.

am thinking a new Fuel Pressure Regulator like the adjustable one from Hesco might be on the list next, along with a good hard look at the MAP sensor, even though FP seems to be in spec when i've checked and nothing is reporting any errors on the DRB Scan tool. just aren't that many things left i can think of to check/change beyond the computer itself, and if i don't get this sorted out in the next few weeks it's gotta' come off the road!

I just got my 1991 tested ... 181,000 miles. Stock.. I'm on the threshold.

15 mph... HC MAX... HC AVG ... HC MEAS... NO MAX... NO AVG... NO MEAS...
...................86.............26................86.............711..............254..............547

25 mph... HC MAX... HC AVG ... HC MEAS... NO MAX... NO AVG... NO MEAS...
..................103............22................58.............613.............173..............500

It appears I'll need to do some work to get it to pass in 2018...

.

 

[zouch!]

PASSED!

problem was found to be due to the distributor having been 'indexed' by the engine installers, as recommended by Hesco. rotating the distributor back and forth while on the tester we were able to get the NOx as low as 44 ppm, though it didn't run very well there.
setting the distributor to where it was close to the original position was enough to get it to where it would pass easily, with room to spare, though it didn't start, idle or run as well as when the distributor was 'indexed'.

so for any of those who have been told that the timing is all controlled by the computer, it ain't entirely true; if you've 'indexed' your distributor by grinding the tabs off and rotating it to where it idles the best, set it back to near stock to have a better chance of passing smog.

 

[jeepsrock]

I know its been a while since my original post, but here we are again and its smog time.

Basically last time, I had replaced & tested a bunch of things (o2 sensor, plugs, CAT) and I was still running lean and as a result failing with high NOX. It wasn't until I had disconnected the Coolant sensor completely that I ended up passing.

I don't think i will have this opportunity again (to disconnect the cts) and quite honestly I would like to resolve this issue once and for all if possible. By reading this and other threads, similar situations were resolved with NEW OEM O2 sensors, new fuel regulators and other things..

Are there any suggestions you guys have with my XJ to go about fixing this ? Is there a way i can rig up some Air/Fuel Guage to help me pin point the culprit, or am i way off ?

Thanks,
Pete

 

[yossarian19]

You are talking about a wide band o2 sensor + gauge. Summit will have options for you.

 

[steveC]

Bumping an old thread, forgive me.

My 94 4.0 HO is currently failing the AZ NoX test (required every 2 years). 2 years ago, it failed the NoX, at about 228K miles on the clock. First time it had failed in the 10 years we've had it. At the time, I suspected old injectors not flowing well, and since I didn't trust them, I decided to replace them all. It took care of the failure...that time.

Sometime back near that time, I had noticed the temp gauge showing uncharacteristically high after 20-30 minutes of driving, not coming down with movement. One day, I caught a lean-limit code on the freeway, and ended up putting a MAP sensor in it, which made it seem to idle a bit better too. Since all the temp sensors were old as dirt, I replaced them all. But never got rid of the temperature creep. Had the 3-row Modine rodded out (radiator guy said it was clean, but had a crack at a hose), did not change anything. O2 sensor is fairly new, at 15K miles today.

This year, with 240K on the clock, I've really struggled with it.

First failure was 3.01 (just over!), and to try and get it past, I dropped the thermostat to 180, and checked it out for vacuum leaks, with a small one found at the MAP sensor fitting. Idle vacuum is right around 16-17" creeping to 18 when it warms up, which seems right.

No luck, went to 4.00 this time (!). Notice that when he's done with a pass on the tester, it's reading hot (not a big surprise, since it's a 4-5 minute road-speed test with just a fan in front). So started looking at everything with a fine tooth comb. All sensors buzz out to the right values cold or hot. Not sure I hear the fan clutch kicking in when I think it should, so I put a fresh one in it. Also found that the ground stud near the rear right side of the block seems a bit loose, so I snug it. Road test seems nice and smooth, and I don't notice any temp creep for a couple of days.

Retest. Fails again at 3.30. Now I'm digging deep...

One thing I note is a bit of a ratty idle that comes and goes. Plugs/wires/cap/rotor are all fairly new (5K miles), plugs are clean with good color. Suspecting that a misfire is likely to throw off the ECU in closed-loop, I try a new coil. That does seem to clean up the idle some, but that temperature creep still shows up here and there.

So, I picked up an IR thermometer to look at the radiator and catalyst. The catalyst shows about a 100F rise, which is what I think it should do. Radiator shows about 180 at the inlet, with about a 10-15 degree drop. That seems right with the 180 thermostat. But the dash gauge (which is out of calibration) shows temps at 190-200 or so I think. Since the sender is right next to the #6 cylinder exhaust port, I still suspect a lean condition due to the heat.

Today, had a little time to look at the O2 sensor with an o-scope, right at the ECU input. Never tried this before. From what I've read, an early MPI setup like this should switch rich/lean/rich at about 5/7 Hz or so (150/200mS). But that's not what I see at all; what I really see is 1 to 1.2 seconds at idle (!), picking up to about 2-300mS when kicked up to 2500RPM or so.

When I first kick it on, it will float around 400mV, then start slowly switching from 200-700mV. After running it awhile, I'll see it go 100-900mV (which should be full range). It seems to spend a bit more time rich than lean, but the lean time could be long enough to get the combustion temps up. Or so I think. I can even "hear" the change in the exhaust to match the switching.

Not having anything to compare it to, this seems like it's working, but the slow rate may be a real problem. Anyone have any data I can compare to?

(sorry that got so long winded...)

 

[blu3fan]

Bumping an old thread, forgive me.

My 94 4.0 HO is currently failing the AZ NoX test (required every 2 years). 2 years ago, it failed the NoX, at about 228K miles on the clock. First time it had failed in the 10 years we've had it. At the time, I suspected old injectors not flowing well, and since I didn't trust them, I decided to replace them all. It took care of the failure...that time.

Sometime back near that time, I had noticed the temp gauge showing uncharacteristically high after 20-30 minutes of driving, not coming down with movement. One day, I caught a lean-limit code on the freeway, and ended up putting a MAP sensor in it, which made it seem to idle a bit better too. Since all the temp sensors were old as dirt, I replaced them all. But never got rid of the temperature creep. Had the 3-row Modine rodded out (radiator guy said it was clean, but had a crack at a hose), did not change anything. O2 sensor is fairly new, at 15K miles today.

This year, with 240K on the clock, I've really struggled with it.

First failure was 3.01 (just over!), and to try and get it past, I dropped the thermostat to 180, and checked it out for vacuum leaks, with a small one found at the MAP sensor fitting. Idle vacuum is right around 16-17" creeping to 18 when it warms up, which seems right.

No luck, went to 4.00 this time (!). Notice that when he's done with a pass on the tester, it's reading hot (not a big surprise, since it's a 4-5 minute road-speed test with just a fan in front). So started looking at everything with a fine tooth comb. All sensors buzz out to the right values cold or hot. Not sure I hear the fan clutch kicking in when I think it should, so I put a fresh one in it. Also found that the ground stud near the rear right side of the block seems a bit loose, so I snug it. Road test seems nice and smooth, and I don't notice any temp creep for a couple of days.

Retest. Fails again at 3.30. Now I'm digging deep...

One thing I note is a bit of a ratty idle that comes and goes. Plugs/wires/cap/rotor are all fairly new (5K miles), plugs are clean with good color. Suspecting that a misfire is likely to throw off the ECU in closed-loop, I try a new coil. That does seem to clean up the idle some, but that temperature creep still shows up here and there.

So, I picked up an IR thermometer to look at the radiator and catalyst. The catalyst shows about a 100F rise, which is what I think it should do. Radiator shows about 180 at the inlet, with about a 10-15 degree drop. That seems right with the 180 thermostat. But the dash gauge (which is out of calibration) shows temps at 190-200 or so I think. Since the sender is right next to the #6 cylinder exhaust port, I still suspect a lean condition due to the heat.

Today, had a little time to look at the O2 sensor with an o-scope, right at the ECU input. Never tried this before. From what I've read, an early MPI setup like this should switch rich/lean/rich at about 5/7 Hz or so (150/200mS). But that's not what I see at all; what I really see is 1 to 1.2 seconds at idle (!), picking up to about 2-300mS when kicked up to 2500RPM or so.

When I first kick it on, it will float around 400mV, then start slowly switching from 200-700mV. After running it awhile, I'll see it go 100-900mV (which should be full range). It seems to spend a bit more time rich than lean, but the lean time could be long enough to get the combustion temps up. Or so I think. I can even "hear" the change in the exhaust to match the switching.

Not having anything to compare it to, this seems like it's working, but the slow rate may be a real problem. Anyone have any data I can compare to?

(sorry that got so long winded...)

Your issue is most likely fuel pressure or spark. or your car is not hot enough when ur going for smog. Drive that sucker hard for like an hour. You want that cat RED RED HOT.
High nox means your running lean/hot
Either engine is too hot. Or more likely u have something creating the lean condition
No if ands or buts about it.
Figure out why you are lean and go from there.
I would highly recommend installing a permanent fuel pressure gauge on the rail. I did. And I do not even have words for how invaluable it is.

 

[steveC]

Your issue is most likely fuel pressure or spark. or your car is not hot enough when ur going for smog. Drive that sucker hard for like an hour. You want that cat RED RED HOT.
High nox means your running lean/hot
Either engine is too hot. Or more likely u have something creating the lean condition
No if ands or buts about it.
Figure out why you are lean and go from there.
I would highly recommend installing a permanent fuel pressure gauge on the rail. I did. And I do not even have words for how invaluable it is.

The permanent gauge isn't a bad idea at all. I have a shop gauge on a hose, but I don't exactly want to leave that on and drive any distance, and it's a pain to connect one to a hot motor. The pressure tests fine sitting in the shop from a cold start, but I've often wondered if it stays in spec over a span of 30 minutes driving.

The coil did clean up the idle quite a bit, but it still just doesn't run quite right somehow.

 

[jeepsrock]

Was the advice of it being fuel related directed to me or Steve ?

Pete

 

[zouch!]

to reiterate what i found on mine,...

have you checked to make sure someone hasn't rotated your distributor to make it run "better"?
it was amazing to see how low the NOx would go as the distributor was rotated back in to place.