High NOX

Looking for some input here. Took my XJ to the inspection station today. It failed NJ's strict emission test. 1) The exhuast was too loud. Kinda figured this with a Flowmaster. Plan on getting a $30 muffler and swapping it just to re-inspect it. But 2) the NOX readings were almost 1000 points over the standard limit. How can this be ? I just re placed everything on the exhuast system, muffler and all pipes... I re used the old converter but it looks good. Could it be the 02 sensor ? I plan on changing it anyway. A friend of my dad's said the EGR vavles tend to stick and wear out after a bit. If it was the EGR wouldn't it lack in acceleration and what not. The engine seems to run perfect. Any suggestions on where else to look and what to try are appreciated.

Thanks,
Doug

opps... 1990 XJ 2.5 Auto 204k

Search with my name and NOX or Gross Polutter, I'm still working on mine but there is plenty of inof on NOX.

also try this, www.passsmog.com

I had this problem on my old chevy truck, and it turned out to be a stuck EGR.

Good luck.

Converter has lots to due with Nox, I would replace it with that many miles and that nox reading. Summitt and Ebay has them for under 75 bucks.

SPVFD47 said:

Looking for some input here. Took my XJ to the inspection station today. It failed NJ's strict emission test. 1) The exhuast was too loud. Kinda figured this with a Flowmaster. Plan on getting a $30 muffler and swapping it just to re-inspect it. But 2) the NOX readings were almost 1000 points over the standard limit. How can this be ? I just re placed everything on the exhuast system, muffler and all pipes... I re used the old converter but it looks good. Could it be the 02 sensor ? I plan on changing it anyway. A friend of my dad's said the EGR vavles tend to stick and wear out after a bit. If it was the EGR wouldn't it lack in acceleration and what not. The engine seems to run perfect. Any suggestions on where else to look and what to try are appreciated.

Thanks,
Doug

Click to expand...

A high NOx is indicative of either a lean A/F mixture or a bad cat. The former is most commonly caused by a stuck open EGR valve on Renix models so I suggest you check that first. Clogged injectors would be another common cause and if you still have the factory originals, you might think about swapping in a set of Ford Mustang 19lb/hr units at some stage.
I also suggest you change the cat. You can find a Carsound high-flow cat cheap in e-bay.

Since the original posting I've changed the EGR Vavle and put the stock muffler and tail pipe back on. It dropped down to be only 259 points over the limit, rather then almost a 1000 points over. So I figured I'd try change the O2 sensor too. A buddy of mine told me to take the air filter out and put a high octane fuel in it and that should lower the NOx by a huge amount. Well I went back thru inspection this morning and the NOx level was over the limit by 1501 points this time. The most so far. I think that maybe taking the air filter caused it, maybe the ecu injected more fuel cause there was more air ? Not sure. I'm gonna put the air filter back in and try to take it back on Monday morning. Till then anyone got any ideas besides replaceing the cat ?

Doug

Not offhand...

High NOx can be caused by a lean AFR (elevating combustion chamber temperatures, and oxidising the nitrogen in the air) or by elevated combustion chamber temperatures (oxidising the nitrogen in the air.)

A lean AFR can be caused by a clogged injector nozzle - either totally or partially, but you'd be more likely to notice if it was totally blocked - or by an intake manifold leak somewhere (check for a vacuum leak.)

NOx is typically controlled by two systems -
EGR/Exhaust Gas Recirculation. This is a "controlled leak" of exhaust gas into the intake stream, which is intended to displace oxygen slightly. This enriches the mixture, because our fuel injection systems read pressure and temperature to meter fuel - but don't do anything to note composition of intake gasses. The EGR can stick open, which will have an effect on emissions, or it can stick closed - which will have an effect on emissions. Also, the EGR base gasket can "burn through," which will cause a vacuum leak.

Redox catalytic convters. Our catalytic converters are actually two-stage devices. The first stange is meant to catalyse the oxidation of CO into CO2, while the second stage "reduces" NOx into N2 and O2. A failing catalytic converter can pass more NOx than normal.

While the manufacturers can say what they will, I don't think I've often heard of a catalytic converter lasting more than 10 years - 15 at the outside. They figure most people won't keep a vehicle that long... So, I'd change the cat, check for a vacuum leak at the base of the EGR, and maybe pull the valve and change the gasket/clean the valve (don't be surprised if the gasket and/or valve are OEMR only.) The EGR can be cleaned with any decent commercial solvent - carburettor cleaner is good - and an old toothbrush. When you replace the gasket, a light coat of RTV copper on both sides will go a LONG way toward an effective seal. Make sure you clean both surfaces before you reassemble.

You might also want to check the EGR valve itself for a leak - you'll need a hand vacuum pump. The engine does not need to be running for this.

1) Disconnect the vacuum line from the EGR valve.
2) Connect the vacuum pump line to the EGR valve
3) Operate the pump to pull 15-18" Hg vacuum on the valve diaphragm. Watch the valve "pintle" and make sure it moves.
4) Watch the gage for two full minutes. You should not lose more than 1" Hg of vacuum. If you do, replace the valce, because the operating diaphragm is leaking.
5) Disconnect the vacuum pump, reconnect the vacuum line.

5-90

Have you done any decarbing? Sea Foam Deep Creep or BK44 seemed to help mine a ton. You have 204k on yours, if you have run cheap gas for any amount of time, it's very likely you have semi clogged injectors or carbon buildup which would lead to HIGH NOX.

clean the egr passage ways and look into getting new cats, possible egr valve sticking or inop. egr wont give acceleration problems, but possible for varying idle.

If the egr has been in poor shape for a long time (you noted changing it) it will have caused damage to the catalytic convert, so did you change the valve or the solenoid, also I would agree the egr passage needs to be cleaned but I would strongly recomend Mopar Combustion Chamber cleaner, this is the strongest combustion cleaner....... I think you should figure on the cat being dead as well....assgas:

Thanks for all the help everyone. I finally got my XJ thru, changed the cat and fuel pump. The standard is 1340 on the NOx and the best I could do before was 1500. Put a new cat on and then the fuel pump died, changed that took her to inspection today and she only showed 63 on the NOx scale. All the other levels were down by about half too since the last trip. The guys at the inspection station were very impressed ! A little birdy told me that the if the fuel pump isn't pumping enough fuel that can actually cause the computer run it a little rich. My scanner says that it runs lean most of the time when before it use to run rich. Hopefully I'll save some gas this way now.

Well the faulty fuel pump explains the high NOX, can't get any leaner than that.

Yea, I didn't want to change the cat because I was still pretty good. And it passed inspection 2 years ago. I wish I had kept the report so I had the readings. Figures with my luck I change something that doesn't really need to be changed and then the problem creater actually carps out making it easier to find and solve the whole equation. It was the original pump to the best of my knowledge. Replaced her with an aftermarket replacement pump from Napa. Its suppose to be a stock replacement but it seems to be a little big. Had a hard time getting her back in the tank. But I can say that she idles alot better now. And the new cat helped bring down the NOx even more. Like I said, hopefully I'll save some money on gas cause the scanner shows her just a tad on the lean side. Where before when I started her up she would be a tad lean and then jump to rich. I think the fuel pump was craping out and the computer was over compensating for it. An electronic geru that I know says the computers can cause that. Anyway I'm happy now that I have a nice new yellow inspection sticker that doesn't expire till March of 2008.