CA SMOG, HIGH NOx

[jeepsrock]

Well I am an Engineer and have a Oscilloscope, so I wouldn't mind taking the time and monitoring the O2 sensor output if it helps me get some useful information, is there some procedure?

Also, does anyone have a good guide on how to check the MAP sensor, all the ones I've seen haven't included data to check at different points weather it be various RPMs and or conditions?

Thanks
Pete

 

[95XJmatt]

You will need to backprobe the oxygen sensor connector signal return and ground to monitor the 0-1 volt switch remember must be around 50milliseconds from the low voltage to high voltage. The only proper way to check a map sensor is with a hand held vacuum pump. One is to check for a leaking internal seal, pump up to 21" and make sure it holds vacuum. You will then need to cycle the ignition on and backprobe the map sensor signal return voltage in correlation to your vacuum gauge to make sure the values match. Map sensor failure is not too common tho.

 

[jeepsrock]

I tested the output of the O2 sensor and its oscillating between 80mV to .9V fairly quickly. If i rev the engine quickly, it dips to the lower end of the scale and then quickly oscillates faster, which i assume is normal ?

As far as testing the MAP sensor, what vacuum pressure corresponds to what voltage ?

Thanks,
Pete

 

[95XJmatt]

Yeah but how fast is fast? You need a scope that will tell you the switch rate in milliseconds to be precise and accurate. For HO engines map us as following;
.39" vac 4.9volts
3.34" vac 4.6volts
6.3" vac 3.6volts
9.25" vac 3.1volts
12.2" 2.6 volts
15.15" 2.1volts
18.11" 1.6volts
21.06" 1.1 volts
24.01" .6 volts
26.97" .31 volts

Again this is for ho engines only 91 to 95 hope this helps.

 

[95XJmatt]

Also when checking your o2 sensor you want to monitor the pattern with the engine at a consistent speed between 1500 rpm and 2000 rpm. If you have a fluke voltmeter or equivalent setup to record with the engine running at that rpm range for a couple mins and see what the min/max/average voltage is. Your average is very important to truly gauge your mixture. Stoich is about 450mv.

 

[BulletMaker]

So any update from the OP as to whether this solved the problem?

 

[jeepsrock]

I plan on,

Flushing the coolant
Checking the rest of the vacuum lines
Running a can of chemtool through the gas tank
Cleaning all sensor connector's
Oil change
Tightening manifold bolts

And getting a base line smog check this weekend and reporting back..

I checked the oxygen and map sensors and they appear to be within specs.

Pete

 

[95XJmatt]

Jeepsrock...

Coolant flush not going to help...
vacuum lines well maybe..
Chemtool waste of time and money not to mention it will poison your oxygen sensor and catalyst
Cleaning connections is not going to help...
Oil change do it for maintenance...

Its so much simpler than this especially since your jeep is not experiencing ANY driveability issues man.. do me a favor just smog your jeep make sure it is warmed up not artificially superheated or any of that then report back on the results.. as a smog/driveability tech dont run anymore garbage thru your fuel tank or intake cleaners your going to create more headaches and will skew your readings for baseline testing. Contrary to beliefs more harm than good comes of fuel system treatments.

 

[jeepsrock]

Well as I figured, I took her in and she failed smog due to high NOX.

Before the test i performed the following...

1. Tightened all Manifold Bolts.
2. Replaced Vac Hose to Canister.
3. Checked Fuel Pressure 32PSI at idle, 41 with regulator disconnected.
4. New Air Filter
5. Cleaned all Sensor Connections.
6. Oil & Filter Change, Coolant Flush.
7. Tank filled with 91 Octane Fuel.

Whats sad about all this is time and time again she fails while running perfectly well.


Measured Number are 358/719 respectively since they arre hard to read.

Advice would be appreciated ?

If all else fails, I am going to try the MAP sensor voltage mod to richen her up i guess...

Pete

 

[95XJmatt]

Wow so close not bad dont get discouraged. Your lambda calculations at 15mph .9999 and 25mph 1.001 which is perfect fuel control. Last culprit remains is your magnaflow catalytic converter. Ive had major issues with them on 4.0 ho jeeps they cannot reduce nox enough. The only true way to prove this is by drilling a small hole pre catalyst and then taking a intrusive gas reading to calculate the catalyst efficiency. As a smog tech this is the only legal way to properly condem the cat. You may need to take it to a smog shop or unless you know a smog guy who wilk run the jeep dyno testing the pre catalyst gases.

 

[JoCat]

This sounds a lot like the last time I had to smog test. Failed with high NOx, but it was running well. Spent a lot of time and money at a gold star smog shop trying to find intake leaks, rebuilding the throttle body, etc. Basically he assumed the high NOx indicated a lean condition or bad cats (2001 has 2 pre-cats as well, but they don't reduce NOx it seems). Had a smoke test to eliminate exhaust leaks, and had holes drilled before and after the main cat to verify its operation, which he thought was bad. Replaced the main cat and still failed. On the recommendation of a mechanic friend I finally took it to Phil's Auto in Hemet. Phil apparently had the highest score ever recorded on the CA state test for his smog license. Anyway, he quickly diagnosed the problem as a small leak in the exhaust from a piece of flex pipe I had clamped in between the manifold and the main cat. Exhaust was pulsing out and air was being sucked in. It was so small the first shop failed to see it on a smoke test, but it was large enough to invalidate the smog probe readings. A quick trip to a muffler shop around the corner to have the flex pipe welded in, and my readings were back to OK. Not as good as the OEM cat, but still a pass. See my post in the thread at http://www.naxja.org/forum/showthread.php?t=1060989.

The best description I've seen is on the FAQ at http://www.thesaabsite.com, but I can't seem to link directly to it. Do a search for "Exhaust Leaks and High NOX Emission (Smog) Test" by Bill Hansen.

Also check out http://www.magnaflow.com/07techtips/TechBulletin/TB80013.pdf. To quote: 'One of the most overlooked problems is that of an air leak upstream of the converter. I know the first reaction is “Who can’t find an exhaust leak”? There have been many documented situations where a leak as small as a pin hole in a weld has caused a vehicle to fail an emission test for excessive N0x.'

 

[Ecomike]

Either the cat, or it is running too lean.

Wow so close not bad dont get discouraged. Your lambda calculations at 15mph .9999 and 25mph 1.001 which is perfect fuel control. Last culprit remains is your magnaflow catalytic converter. Ive had major issues with them on 4.0 ho jeeps they cannot reduce nox enough. The only true way to prove this is by drilling a small hole pre catalyst and then taking a intrusive gas reading to calculate the catalyst efficiency. As a smog tech this is the only legal way to properly condem the cat. You may need to take it to a smog shop or unless you know a smog guy who wilk run the jeep dyno testing the pre catalyst gases.

 

[jeepsrock]

I am not discouraged, just frustrated considering how she runs and is maintained.

I was under the impression that a Lambda value that close to 1 is almost perfect, how can i be running lean ?

The CAT has been double replaced and is less than a year old, i doubt that its bad or not effective. Does anyone know of a shop in the San Fernando Valley that will be willing to check for leaks and or check the cat cheaply and reliably ?

Thanks,
Pete

 

[jeepsrock]

Bump..

 

[95XJmatt]

Being that your jeep is the year with only a single catalyst not the dual at header theres likely no exhaust leak present... only place to leak is the flange donut gasket or shottie welds around the inlet of the catalyst. Being that you were down there scoping the oxygen sensor Im sure you already checked that, however a smoke check would help but is tricky to do so. I know beating a horse to death but you didnt mention your oxygen sensor switch rate. My readings were identical after replacing the manifold then catalyst, then the oem oxygen sensor brought nox to under 50ppm.

 

[Ecomike]

Bump..

Do not underestimate the stealthiness of a leak, intake or exhaust leak.

I had a donut leak blowing on the block at high RPMs , like 2000 rpm causing my engine to over heat once fully warmed up after a long drive or 30 minutes of idling, that escaped multiple inspections for 6 years. It was just enough added heat to the oil pan to run mine up 235F in the summer with A/C on. New donut and mine never gets over 210 F under the worst conditions.

Also carbon build up in the cylinders can cause a lean condition per 5-90 IIRC. Not sure about lambda readings, but your low HCs says it is running too lean for the Cat to be able to work right. Cats need the engine to run a little rich to fuel the Cat Converter. Running at true stoich is too lean for the Cats to reduce the NOx.

 

[95XJmatt]

No actually a lambda reading of 1 is perrrrfect for catalyst operation if your looking at a true automotive calculator that shows you operating ranges. The job of the oxygen sensor is critical in keeping that constant rich/lean toggle thus lighting the catalyst off. Im telling you on these engines it is critical! His NOx levels are so close that it is not going to be carbon buildup not to mention all the cleaners he has already ran thru the intake. The ONLY time I have seen it be effective is when they gross pollute on NOx or if there is a true internal enginr problem like valve seats/valve face.

 

[Locked98GC]

Throwing this in here for info only.

Putting my stock 95 XJ on this list. I failed for NOX, installed a Bosch O2 sensor and Walker 80905 CA cat. The NTK went bad within the last 2 years and somewhere in there 1/2 the cat blew away. Failing with NOX in the 750 range on low and high speed test 2. More things to look at tomorrow.

 

[95XJmatt]

Either exhaust leak or your having fuel control issues with the bosch oxygen sensor making it run on the lean side. I would never install a bosch o2 in my nor my customer's jeeps

 

[jeepsrock]

Well I inspected the exhaust thoroughly today and found no leaks whatsoever, i was hoping i would find a small one or something..

Locked98GC, you oddly have similar readings, where you able to make any progress on your Jeeps issue ?

Pete