CA SMOG, HIGH NOx

[jeepsrock]

The Jeep has failed CA Smog due to high Nox.
You can see the progress below and what i have done, i have no clue how else to go forward. Suggestions would be highly appreciated...


First Run.
* Checked Coolant Level and Aired Tires.


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Second Run.
* New O2 Sensor (NGK 23023), Air Filter & Fuel Filter.
* SeaFoamed Engine.
* Checked for Vac Leaks.


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Third Run.
* New Magnaflow Cat (39005).
- Strangely NOx levels went higher ?


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Pete

 

[Ecomike]

It is running too lean (and or too hot) for some reason. We need to know what year jeep it is next!

Other repair history? Plugs, wires, cap, rotor, Sensor tests, like CTS and IAT temperature accuracy....

 

[Tuffnuttz]

Check EGR and catalytic converter.

 

[Ecomike]

Check EGR and catalytic converter.

Read his post, the third step was a new Cat (magnaflow), and the NOx went even higher. EGR was only on Renix, 87-90, not on HO years 91-01, and we do not have the year spec yet from the OP.

Edit: I just checked the O2 sensor he used. It does not fit Renix, but fits HO years, so if he bought the right O2 sensor, his engine is an HO, 91-01, and does not have an EGR.

So that leaves a problem with O2 sensor wires, like the O2 sensor heater power relay and 12 volts to the O2 sensor internal electric resistance heater, or the computer, or a bad CTS, IAT, temp sensor(s), or a vacuum leak near the MAP sensor vacuum hose biasing the MAP sensor data, or a bad cooling system, letting the engine run too hot!!!!! Oh, and Exhaust manifold leak (gasket, crack or donut leak) could be confusing the O2 sensor!!!!!

I should not be ignition related, or even mechanical engine related (based on the low HC and low CO numbers), unless the cooling jacket is scaled up.

 

[jeepsrock]

1994 Jeep Cherokee
4.0 6cyl
50 Series Flowmaster
Aftermarket Manifold installed ~6months ago.

Aug2011 (TuneUp)
* Coolant Flush
* Champion Plus and Rotor/Cap
* Oil Change & Filter
* Tightened Manifold/ Collector Bolts


All other sensors are at least 6-7 Years old.

Thanks so much folks,
Pete

 

[5-90]

Correct heat range for plugs? Try going one colder, and see if that helps bring temperatures down.

Can you get to look through the spark plug holes somehow? You may carbon deposits, which will insulate the metal and prevent drawing off chamber heat and elevate combustion temperatures. I've posted elsewhere on how to deal with that easily and cheaply. Since it's a 1994, it may be due to be decarbonised anyhow - but it would help to get a look in and see what's going on down there.

New cat, no EGR OEM, so that shouldn't be at issue. It's not the after-treatment of the exhaust gas, it's not a failure of exhaust gas recirculation, although (given your HC and CO results,) I'm inclined to say you're running slightly lean. Try an injector cleaning as well.

 

[Ecomike]

Aftermarket manifold may be part of the problem. No way I know of to confirm that. Have you checked for OBD-I codes with the key on-off, on-off, on....flash count light number count method for error codes?

I would get out the FSM and check the CTS and IAT temp sensors, hot resistance for bad data versus FSM data tables of resistance versus temp. Check the O2 sensor live and the 12 volts to the O2 heater and the two O2 sensor ground wires for resistance above .5 to 1.0 ohms....

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=oxygen+sensor+test&page=7

What temps is the cooling system running at?

If it is running rich at idle due to a bad O2 sensor wire or heater voltage relay is bad, or bad wire, it could be running rich at idle, adding carbon the combustion chamber, than running too lean at loaded higher rpms due to carbon fouling, but I check that the O2 wiring is all good first, as a bad connection or wire can corrupt the data the ECU sees from the O2 sensor biasing the ECU to run the engine too lean because it thinks the engine is too rich.

 

[Ecomike]

Correct heat range for plugs? Try going one colder, and see if that helps bring temperatures down.

Can you get to look through the spark plug holes somehow? You may carbon deposits, which will insulate the metal and prevent drawing off chamber heat and elevate combustion temperatures. I've posted elsewhere on how to deal with that easily and cheaply. Since it's a 1994, it may be due to be decarbonised anyhow - but it would help to get a look in and see what's going on down there.

New cat, no EGR OEM, so that shouldn't be at issue. It's not the after-treatment of the exhaust gas, it's not a failure of exhaust gas recirculation, although (given your HC and CO results,) I'm inclined to say you're running slightly lean. Try an injector cleaning as well.

See OP, he seafoamed the engine (and installed a new O2 sensor) between tests 1 and 2, and NOx increased. Then he replaced the Cat between steps 2 and 3, and NOx got worse.

I hope he seafoamed, before he replaced the O2 sensor?

Note: He did not say how he seafoamed the engine. Perhaps he just cleaned the intake and added carbon the the combustion chamber?

 

[5-90]

See OP, he seafoamed the engine (and installed a new O2 sensor) between tests 1 and 2, and NOx increased. Then he replaced the Cat between steps 2 and 3, and NOx got worse.

I hope he seafoamed, before he replaced the O2 sensor?

Note: He did not say how he seafoamed the engine. Perhaps he just cleaned the intake and added carbon the the combustion chamber?

Could be. I probably glossed over the Seafoam part, but "Seafoaming" the engine still leaves some open ground (you can dump it in the intake - should get carbon, won't do anything to the injectors. You can dump it in the fuel - should clean the injectors, but won't do much against chamber carbon.)

I'm still leaning toward the mix being slightly lean - the reason I ask people to post all measured results from a failed smog is because they're all instructive.

Granted, his O2 is measured at zero, which kinds throws off the "running lean" bit. And, the CO2 is about right. It's the elevated NOx without a significant reduction in HC and CO that throws me a bit...

 

[Ecomike]

Local smog guy here swears that running the cleaners through the injectors (gas tank) and the intake (via vac hose), has always fixed jeeps that failed just the NOx by a little bit, where everything else was already good, so you may be right about injector cleaner on this one, but I think he should also test the basic sensors. He should also check the spark plug number (which I do not think he posted, just the brand and type) he is using to see if they are too hot?

I had not looked at the O2, it is not always listed, or accurate in other states. Could near zero O2 affect NOx? Most curious trend in his O2 numbers!!!!
.2-.3 test one, then higher on test 2, .3-.4, then zero on test 3 with the new cat??????

I wonder if the tester is bad? But the HC dropped 10 fold on test 3!!!!

Any data available on aftermarket headers raising emissions?

I wonder if "seafoaming the engine", means the oil, intake manifold or gas tank now, LOL?

"Answer only import if ask right question" LOL. Next Karate Kid,

 

[5-90]

Theoretically, you want to have zero O2 remaining - it shows that the fuel being delivered is sufficient.

You also want to have nearly no HC or CO - because either of those represents unburned or partially-burned fuel, respectively.

NOx isn't a product of combustion, it's a product of combustion temperature, which makes it a "flyer" on emissions testing results (HC and CO are from fuel not burning correct, CO2 is from fuel being burned properly, O2 is what is needed to burn the fuel. CO2 is going to be fairly low because it's almost naturally low enough to be considered a "trace gas," and the atmosphere only runs about 20-22% O2 anyhow (it's 70-odd percent nitrogen tho...)

Y'know, so much of the emissions headache could be avoided (and tailpipe emissions reduced to nearly nothing) if they would just allow us to use water/MeOH fogging in place of the wretched EGR system (and you could tune an engine to run much better on the fog than on EGR!)

 

[ferntr33]

You all sound like you know a lot more than I, but did you make sure the cat you got is the right cat for CA pre 1996? You might have gotten some douche who put the non CA cat on or something . . . maybe worth looking into.

 

[kdailey4315]

How is your coolant temp sensor your cooling system in general? Is your jeep running hot? Higher temps can lead to higher NO.

 

[jeepsrock]

Earlier today i checked the fuel pressure just for kicks, its about 34psi at primed cold state/engine off and varies from 32-38psi revving the engine.

The Seafoming engine treatment I mentioned was 1/2 a can down the Brake Booster Vac tube and the other 1/2 down the Fuel Tank which was indeed before the O2 replacement. I let it soak about 15mins and ran it on the highway a bit till the smoke stopped.

As for the Spark Plugs, i always use the recommended Champions since they have typically worked and felt the best. I haven't checked them lately since it seems a little premature ?

The Jeep Runs right in the middle as far as temperature, if it happens to climb up, the e-fan brings it right back down, which is normal as far as i know.

The manifold i am running is one like this,
http://static.1aautoimages.com/partimage/EEM/1AEEM00146/large.JPG

I will try to test the sensor data using a multimeter as mentioned above, in the mean time keep the ideas coming, i really appreciate it...

Pete

 

[Ecomike]

I am not positive, but IIRC HO engines need 49-50 PSI fuel pump pressure!!!!!

You may have a bad check valve or loose hose in the fuel tank or a weak ground, thus slow pump speed?????? Loose hose or leaking fuel pressure regulator in the tank are common.

Also check that the fuel filter is good, install the right direction, and check for crushed fuel line tubing from the engine to the tank!!!

 

[Ecomike]

Theoretically, you want to have zero O2 remaining - it shows that the fuel being delivered is sufficient.

You also want to have nearly no HC or CO - because either of those represents unburned or partially-burned fuel, respectively.

NOx isn't a product of combustion, it's a product of combustion temperature, which makes it a "flyer" on emissions testing results (HC and CO are from fuel not burning correct, CO2 is from fuel being burned properly, O2 is what is needed to burn the fuel. CO2 is going to be fairly low because it's almost naturally low enough to be considered a "trace gas," and the atmosphere only runs about 20-22% O2 anyhow (it's 70-odd percent nitrogen tho...)

Y'know, so much of the emissions headache could be avoided (and tailpipe emissions reduced to nearly nothing) if they would just allow us to use water/MeOH fogging in place of the wretched EGR system (and you could tune an engine to run much better on the fog than on EGR!)

I disagree on two points (possibly typos?), one is the theoretical zero O2. I suspect it takes a good bit of excess O2 to reach the 14.7 stoich number, since that is not an excessively high rich burn number. I have also seen test data showing multiple percent excess O2, but that may have been tailpipe 6X dilution numbers on the O2, so the data is not always on equal footing. I could be wrong on that?

The other I think is a typo: " CO2 is going to be fairly low because it's almost naturally low enough to be considered a "trace gas".

The O2 is replaced by CO2, so if O2 goes from 21% to zero, the CO2 will go way up as the O2 is replaced by CO2. I have seen CO2 numbers average around 14% in many reports, which would suggest 6% remaining O2, but there is a huge increase in H20 gas that dilutes them all that is not measured or reported, and I have seen O2 numbers reported well below 1% on many reports (which is why the O2 numbers running from 6% to under 1% have always puzzled me so far. Only thing I can figure is the O2 reported is sometimes a diluted O2 due to tester differences, and the huge increase in CO2 and H20, from fuel combustion, dilutes the N2 and remaining O2....)

 

[O-Gauge Steamer]

Early HO engines operate at 39psig nominal fuel pressure. I am not sure when the brake happened, but I suspect 95 down to be the lower rail system. If the rail has a return line then there you go. 93 HOs definately have the lower pressure. Leastways on YJs they do and I can not imagine two fuel systems in the OBDI years...

If it is a 95- HO, the pressure should be 39lbs. The regulator is connected to the manifold and varies the correction of the fuel pressure based on the manifold vacuum level. Under low vacuum (accelerating) the regulator allows more fuel to stay in the rail.

Sounds like it is going lean due to fuel starvation. Cleaning the injector goes a long way but sometimes, another set needs to be installed. Personally, I'd take a stab at the fuel pressure to get it back to nominal.

 

[Ecomike]

If the HO-OBD-I years (91-95) are indeed the same as Renix on fuel pressure, then his numbers he posted are perfect on fuel pressure. Mine runs from 29-41 max, and his post was a tighter range:

"its about 34psi at primed cold state/engine off and varies from 32-38psi revving the engine" which is just fine. So it sounds like we can eliminate the fuel system as an issue.

Since you have not checked the plugs, check them next to see if the color is off on any plugs, indicating that one or more cylinders are running too lean and too hot?

I wonder if premium gas would lower engine and Cat temps a little, and thus lower the NOx a little?????

I also wonder if adding some methanol or acetone might lower the combustion temps enough to pass it, but that is more of a desperate move, chat idea for now?

 

[jeepsrock]

First question is, can low fuel pressure cause the engine to run perfectly but result in a slightly lean condition ?

Second question is, where can i actually find out what the pressure is supposed to be under different condition for my year ? My Haynes book seems to be worthless for things like this, all my searching online results in info for very early Renix XJs or recent model ones ?

Thanks,
Pete

 

[Ecomike]

First question is, can low fuel pressure cause the engine to run perfectly but result in a slightly lean condition ?

Second question is, where can i actually find out what the pressure is supposed to be under different condition for my year ? My Haynes book seems to be worthless for things like this, all my searching online results in info for very early Renix XJs or recent model ones ?

Thanks,
Pete

If there is a vacuum operated valve on the front of the fuel rail, and a hose at the rear of the fuel rail, you have the Renix fuel pressure regulator set up, and your pressures are fine, so they are not the droids you are looking for, LOL.

http://www.autozone.com/autozone/re...hildCategoryNameForTitle=Fuel+System+Pressure


"31-39 PSI (Pounds per Square Inch)Position the ignition switch and the A/C system in theoff position. Install a fuel pressure gauge to thevehicles fuel rail or fuel pressure test port.Confirm that no leaks are present, and visuallyverify the PSI reading on the gauge with the ignitionin the on position."

Have you pulled the spark plugs, and inspected them???