Failed NJ Emisisons - Help?

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Sep 23, 2005
Hi! OK, so this is the first time this car has failes the NJ emissions test! Just wanted to see what people think as to why, and maybe what I can do to fix. Its a 92 Nissan Sentra with 189,000 on it. Failed NOx (standard is 1242, Nissan was 1788) Failed HC (standard is 159, Nissan was 187) Passed CO (standard% is .89, Nissan is .43%) Passed CO2 (read 12.4) Passed O2 (read 1.5) This is the first time it has failed. I've been running a steady diet of Shell regular gas, and I put a bottle of Regaine in the tank about 3 weeks ago to prep for the test. I'm also in the final rinse stage of an Auto-RX "high-mileage" treatment if that means anything. In the spring of 04, I put in a new O2 sensor, new wires, plugs, fuel filter, rotor and cap, new PCV valve, and it passed that inspection OK. So, based on that info, does anyone have any thoughts? Anything stand out as obvious? I'm going to replave the air-filter as I do each Fall, and replace the PCV valve, but not sure what else to do just yet. Thanks in advance!!!
Shell, in many states, doesn't use ethanol in it's gas. There is/are fuel adds that help with the smog tests. Try those just before the test and a tank or two of a quality 'gasahol' before the re-test. Be done with the RX treatment, it may not have anything to do with the results you've got but it is a variable, so try a fresh oil change just before the test. My 2¢
I'd pull the plugs and take a look at em. Also, clean out the TB and maybe even a seafoam treatment through the PCV.
Interesting...Does anyone know what brands typically do sell the ethanol blend of gas, and does anyone have any success with an "emissions" kind of fuel additive? Gonna check the plugs now to see how thaw look! Thanks again!
One way to get booze in your fuel is to run the tank low and add a few 12 oz bottles of "Iso-HEET" drygas.
If those are exhaust gases, i wuld think something maybe wrong with the catalytic convertor or exhaust system somehow. Check to see if its plugged. It would be good to have a cause and effect sheet to quickly determine problem area from emissions results.
Do you have an EGR system on that thing? It reduces NOx emissions, so it might have some trouble since your NOx is too high.
OK. Plugs are not bad, but a little "greyish" - no oil on them. My records indicate I did them in April 04 with about 155,000 miles. So, they have about 30K on them, but the Platimum plugs called for are supposed to go 60K. I can switch them easily enough though. Yes, there is an EGR valve on the car that does not look like it would be too horroble to replace. That is still original to the car. Thanks!
So you got they dyno test then, eh? My 91 BMW 318i had similar NOX numbers, but much lower HC readings. My car does not have an EGR. Im no magic emissions reader, but Id venture to guess that your cat converter is not lighting off to the point to fully convert HCs, though it is operating well enough for the oxidation of CO. One reason I say this is because you still apparently have an excess of oxygen in there, so I think it is a catalytic equilibrium issue, rather than anything else, especially given your plugs looking OK. For NOx, Id look at your EGR. It may just be a cleaning issue, or perhaps it needs a replacement. Pull it (get a new gasket first) and see if it of the port it sits in looks fouled or gummed up. IMO, if NOX was up and HC down, you might have a timing issue, but I think that youre close and all is nearly well... Definitely run a shock dose of a decent cleaner through the tank, and preferably through the PCV as well. Good luck! JMH
Another thing you might do on the way to the re-test; run the snot out of it just before the test. Gets the converter nice and hot and may blow some carbon out of cylinders as well. My 2¢
Thanks again for all the tips. I'm going to do what I can and take it for a reinspection next month. Ultimately, it might be the cat that needs replacement, but that might be high enough ($$$) to qualify for the waiver. We'll see. I took it up on the highway before the test, then, I ended up sitting in line for an hour before I was tested! I was reading on some other forum that if you have to sit idoling for awhile, it makes sense to keep the RPMs up to keep everything hot...
NJ, I don't know about NJ. But in Pennsylvania you have a lot of "wiggle room" if you're car is pre-1996. I've learned that my own smoker, a 1991 civic, burns less oil right after a fresh oil change. (i burn more oil after prolonged use)
Your CO2 is low. It should be around 15%. Newer cars may even have it as high as 16%. CO2 is an indicator of combustion efficiency. Higher CO2 is always better. Your mixture and O2 sensors are probably OK, otherwise CO (carbon monoxide) would be much higher if you were running rich. Carbon buildup in the heads can increase NOX and HC. Decarbonize the heads with GM Top Engine Cleaner or SeaFoam. It can also burn off some of the contamination on a tired catalytic converter. Your EGR might be working fine. It is often the EGR passages which get clogged and need to be cleaned. No easy way here. A piece of steel cable chucked into a drill can often root out the passages. Lastly, the catalytic converter may be tired. If it is the original and you have almost 200K miles, it has served you well. Time to retire the old converter. It probably is not any one thing causing you to fail, but the cumulative affect of many small things, in addition to the tired cat. But replacing the cat without taking care of other issues is only a bandaid, not a real fix. Good luck. Persevere and you will succeed.
your Nissan is running a tad rich. BTW, my 88 528e just passed MA emissions at 332k miles on its original cat. NOx was 50% of the failing spec, HC about 25%, CO less than 10% like previous readers said, change the oil, and air filter, fresh plugs too. I got a tank of 93 octane just for test purposes. And get that cat hot.
Thanks again everyone - I do appreciate it! I'm going to follow the advice and change out what I can, clean what I can and retest. A new EGR is going to cost $110 (ouch) If it fails again, then the cat will be replaced as well. If it fais after that, well, lets hope it doesnt!
try to clean that EGR before replacing it... you might be able to test it while running, though usually EGR requires throttle opening to operate... check with more experienced folks to see how to test an EGR valve for operation... JMH
I think you are misreading the emissions numbers. nj300se's engine is actually running lean. Although it is true that he failedfor slightly higher HC, that in and of itself is not a sign of running rich. A prime example of this is what is known to emissions people as a lean misfire. A lean misfire will produce huge amounts of HC emissions, but the reason is that the engine running too lean for the fuel to ignite, and the raw mixture gets dumped out the exhaust. A lean misfire is an extreme example, but anything that can keep fuel from burning will raise HC. Carbon deposits soak up gas during intake stroke and release it during exhaust stroke. This gas isn't vaporized so it doesn't burn and comes down the pipe raw. Cool combustion chambers can keep gas from vaporizing, but we know this can't be the case because in nj300se's engine because the NOX is so high. NOX formation requires very hot combustion chambers, on the order of 2500° F. Rich engines run cool. Lean engines run hot, and produce more NOX. For diagnosing the cause, the most important gases to look at are CO, O2, and CO2. CO is a very good indicator of richness. CO will start to climb rapidly even before excess HC shows up noticeably in the exhaust. However, CO is not a good indicator of how lean an engine is running. Once an engine goes leaner that stoichiometric, CO flattens out and doesn't tell us much. O2 on the other hand is a not a good indicator of richness, but it will tell us how lean an engine is running. O2 starts to climb on the lean side of stoichiometric. This is because with lean conditions there are fewer HC molecules to unite with the O2 molecules. The leaner you go, the more O2 there is. With a lean misfire O2 will skyrocket. Finally, CO2 is a good indicator of combustion efficiency. CO2 should be above 14% at the minimum. Higher is better.Low CO2 tells us that for what ever reasons, combustion is not efficient and the HC and O2 molecules are not uniting as they should. In the case of nj300se's engine, we have over three times the percentage of O2 as CO. This indicates an engine running a bit on the lean side. A vacuum leak could cause this. Old leaky injectors which dribble instead of spray can cause this. Dirty carbonized combustion chambers can cause this. To reduce NOX you want the combustion chambers to run cooler. Good flow in the cooling system through the heads will reduce NOX. An out of spec coolant temperature sensor can cause an engine to run hotter; make sure the ECT is in spec. Worn impeller blades on the water pump can make the heads run too hot. Running richer cause cooler combustion and will reduce NOX. Clean combustion chambers and lower compression will lower NOX. Avoiding detonation will prevent NOX. Always run high octane gas when you want help passing a NOX emissions tests. De-carbonize the cylinder head, which lowers compression, allows for better heat transfer, and more efficient combustion. De-carbonized heads will produce less NOX and less HC. EGR reduces NOX by reducing the oxygen content of the mixture. This serves to effectively enriches the mixture as itforces the ratio of HC to O2 higher. It also causes the combustion to occur slower and cooler because there is less oxygen to fan the flame. This also prevents detonation and knock. Unfortunately, many EGR valves are replaced without cleaning the EGR passages in the manifold. Often the EGR valve itself is good and the passages are choked with carbon blocking EGR flow. Always check the passages before replacing an EGR valve. I think a good emissions tech could get nj300se's car through emissions without a new cat. But finding a good emissions tech can be a problem. Japanese cars rely heavily on the catalytic converter for NOX reduction. My advice for nj300se would be to take care of all the small things which can be done, and then replace the catalytic converter with a new OEM unit.
Wow vizvo. Hats off to you and thanks for putting in the time to write all that. Great info!
Quick follow up...To clean the combustion chambers, someone mentioned Seafoam. Is cleaning the combustion chambers the same thing as de-carbonizing the heads? Would a product like Seafoam do both? You guys rule!
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