CA SMOG, HIGH NOx

I have never believed the local folklore here that NTK O2 sensors are way better than Bosch. The Renix sensor was invented and was OEM from Bosch. That is what I use. All my rigs are Renix, and most here say NTK is best for the HO rigs. The real story is to pull out an analog volt meter and test the dam things with an O2 bottle, and flame from a torch, and to test the wiring internals for about 8 ohms on the internal resistance wire heater, and test for the voltage to the sensor and to sensors heater... test the ground and so on.

Is your rig Renix or HO? Year?

This could be a good lesson for everyone having NOx smog test issues!!! It is called bias, and it is hard to test for with out a CO2 and O2 feed bottle and flow measurement meters to run the O2 concentration up and down in a quantifiable way. May be a good thread idea folks!!!! Bottles are cheap, just need good lab flow meters.

Congrats on saving the jeep and fixing your problem. Took me years to solve of my never seen before, Renix sensor problems, LOL.

:cheers:

snooop1e said:

SOLVED!!! I PASSED!!!

I replaced the BRAND NEW OEM NTK oxygen sensor with a BOSCH oxygen sensor and dropped Nox from 1600 and 1500 to 10 and 0.

Which means I spent over $900.00 and approx 40 hours working on my Jeep, missed several days of.work and failed 5 smog tests simply because a BRAND NEW NTK oxygen sensor was sending bad data to the computer indicating a rich AFR so the computer leaned out the AFR Thanks NTK!

Click to expand...

snooop1e said:

SOLVED!!! I PASSED!!!

I replaced the BRAND NEW OEM NTK oxygen sensor with a BOSCH oxygen sensor and dropped Nox from 1600 and 1500 to 10 and 0.

Which means I spent over $900.00 and approx 40 hours working on my Jeep, missed several days of.work and failed 5 smog tests simply because a BRAND NEW NTK oxygen sensor was sending bad data to the computer indicating a rich AFR so the computer leaned out the AFR Thanks NTK!

Click to expand...

When I switched my '91 XJ dash board from idiot lights to the xj gauge cluster, I installed an NTK temp sender (on the back of the engine head, driver's side). It was totally off. I replaced it with a genuine mopar, and it worked beautifully. I also have a Bosch O2 sensor, and it's always worked well.

Here we are again and its time to get the Jeep smogged. If you follow the thread from the beginning you'll see that every other year since 2012, no matter what i did i always ended up having to unplug the CTS sensor to get the Jeep to pass smog with decent NOX values Hasta

This time instead of wasting time for what could not have been fixed over several years i want to have a better idea of what actually happens when the CTS is disconnected ?

Does it assume max resistance value and thus extra cold causing it to richen the mix ? Or does it realize there is no sensor (due to the infinite resistance) and use a predetermined value, if so what is that value ?

Thanks,
Pete

Is it an HO, OBD-1 or II or Renix? What year?

Old_Man proved that a bad CTS on his Renix made it run rich, kept it from ever reaching closed loop operation, it drank gas all the time. Your test Data is wrong for an engine running rich and running in open loop, it is the opposite.

Has the CTS been tested at 0*F and and 212 F in ice water and water boiling water to see it meets OEM specs? Was it replaced with a tested CTS??? Is the CTS telling the computer the coolant is hotter than it really is?

Is the CTS wiring shorted, or making the engine run too lean?

Are the CTS e-connectors clean and tight?

Is the CTS ground wire reading less than 1 ohm to the battery negative post (Renix rigs)

It's a 94 HO OBDI Jeep XJ

My question is a bit different, I am asking what does the computer assume when the CTS is disconnected?

Pete



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jeepsrock said:

It's a 94 HO OBDI Jeep XJ

My question is a bit different, I am asking what does the computer assume when the CTS is disconnected?

Pete



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Click to expand...

I will repeat, it assumes the engine is very cold, to protect the engine from running too lean and burning up the engine, and so it runs the engine super rich. Your test data was lean, not rich, so my guess is that when you disconnected it, there must be a short in the two CTS wires in the harness telling the computer the engine is warm or hot, enough for it to go closed loop anyway.

Ecomike said:

I will repeat, it assumes the engine is very cold, to protect the engine from running too lean and burning up the engine, and so it runs the engine super rich. Your test data was lean, not rich, so my guess is that when you disconnected it, there must be a short in the two CTS wires in the harness telling the computer the engine is warm or hot, enough for it to go closed loop anyway.

Click to expand...

Yes I'm definitely running lean, no doubt about that..

When the CTS is disconnected, it immediately throws a check engine lamp. To me this means that the computer is able to differentiate between extremely cold temperature (-40deg) the sensors max cold read and complete disconnected state.

If there was a short in the harness then no matter connected or disconnected it would result in a very small resistance thru the short... Is my thinking along the right lines or no?

Thanks,
Pete


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OK, now I am confused, I thought you said you disconnected the CTS and passed emissions doing that last time? How is that possible if it throws a code when you disconnect it???

You can test the CTS with an ohm meter and temp gauge at 3-4 temps to see if it is accurate. If it is not, it could be biasing the ECU timing a bit. But running lean usually means too little fuel and low fuel pressure, or dirty injector(s).

Sounds like the harness is ok, yes!!! One down!!

Ecomike said:

OK, now I am confused, I thought you said you disconnected the CTS and passed emissions doing that last time? How is that possible if it throws a code when you disconnect it???

Click to expand...

Let's just say the check engine light wasn't seen...

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jeepsrock said:

Let's just say the check engine light wasn't seen...

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Click to expand...

:gag:

Have you replaced the CTS with a know to be good, tested and proven to be accurate CTS????

Tested the IAT and the CTS externally, values look right on both cold and warm.

Took it to the smog tech to run it manually and get some general NOX values to know where we are, 700+

Anyone locally here want to have a whack at it or know someone who would.... Perhaps it's timing related?

Pete


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Something that might be worth noting here...

The Jeep starts right up when its cold, but when its warm it takes some cranking to get it started and when it starts it isn't very smooth for a few seconds ?

Pete

jeepsrock said:

Something that might be worth noting here...

The Jeep starts right up when its cold, but when its warm it takes some cranking to get it started and when it starts it isn't very smooth for a few seconds ?

Pete

Click to expand...

Sounds like a bad IAT Intake air temp sensor, but a loose ground or sensor connection can be temp sensitive. Have you tested the IAT and MAP sensor with a calibrated vacuum test rig, temp sensor and Volt/Ohms meter per the FSM???


If the IAT is bad, you may have biased the computer calculations with the disconnected CTS and thus solve the lean issues while the CTS as off line???

Ecomike said:

Sounds like a bad IAT Intake air temp sensor, but a loose ground or sensor connection can be temp sensitive. Have you tested the IAT and MAP sensor with a calibrated vacuum test rig, temp sensor and Volt/Ohms meter per the FSM???


If the IAT is bad, you may have biased the computer calculations with the disconnected CTS and thus solve the lean issues while the CTS as off line???

Click to expand...

Take a look..

Pete


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jeepsrock said:

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

Click to expand...

You test it with a hand vacuum apply to the vacuum nipple, and pull various stable vacuums amounts on it and test the resistance, or the live voltage output, against the Factory FSM data table.

Is the O2 sensor new, with no change in the problem, is it Mopar or what brand?

Have you run a compression test, and rechecked the spark plugs since a year ago, for any difference in color or fouling, and thus a possible lean or rich cylinder clue throwing the O2 sensor off balance? All it takes is one lean cylinder, cause by the other(s) being rich, or caused by a partly clogged injector making one cylinder too lean.

Are there any, ANY other operating issues at all, or anomalies???

Impressive, most impressive post!! It looks pretty darn close to spec, here is a link to the date table for the OEM spec

http://www.fixjeeps.com/iat-sensor.html

and

https://www.cherokeeforum.com/f2/coolant-temperature-sensor-testing-188821/

So that leaves the MAP being biased, (or a wiring resistance issue, which I doubt). Be sure to test the engine vacuum at the MAP hose if and when you test the MAP

or a fuel injector issue,

or spark plug or compression issue I think???

Or maybe the distributor needs indexing if all else fails.

I would use a better spark plug, but your photos look fine, but what do the plugs look like now???

I read one or two folks that had to buy the Ca Cats to get their NOx into compliance. Did the current Cat ever pass?

But that said, IIRC the low HC report makes it look like (looks can be deceiving) it is running too lean, and the Cat needs extra fuel to get hot enough to remove the NOx while it burns the excess fuel!!!

5-90 use to post up here that carbon on the valves/pistons can cause the high NOx.

Some guys here have "water-borded" (LOL) their jeeps to remove some of the carbon. I found that removing the spark plugs, and adding MMO ( about a table spoon) overnight to the top of the pistons, and then cranking the engine with out the plugs in yet, gets rid of a lot of carbon build up on piston rings (On my Saturn that was so fouled it was using a quart of oil in 200 miles, now it is about 2000 miles/quart), so it might work on the piston head etc.

Does it ping on acceleration at all???

But all I suggest is keep testing. Loved the test photos of the IAT!!! Not sure why I never thought of using a hot air dryer for that

jeepsrock said:

Take a look..

Pete

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Click to expand...

So here are the test results of the MAP sensor at 5,10,20 in Hg vac, what's next..

Seems to match the data I see online :/

How do I test the timing and distributor indexing?

Pete

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See www.cruiser54.com chapter on Dizzy indexing. Ask him if it applies the 1994 HOs.

Fuel pressure,

Idle 31psi
Idle vac disc at reg 40psi
Revving engine 29-30psi

Pete


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Something to add here, might be a helpful tidbit.

The jeep is starts right up when cold, but after getting warmed up it takes several cranks to start up and it stumbles for a couple of seconds before smoothing out..

Pete


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