I just went for an emissions test with my 1999 LD9 fire and having a few problems. My CO and HC reading were adequate however my NOX reading was overly high. I spoke with the tech and all he did was try and make me play the guessing game since he dosnt have a 5 way fuel analyser. Now i understand, its hard to diagnose a vehicle without getting it tested using certain tools and scanners however. I was wandering whether this is common for a 1999 2.4 (without EGR's). Higher NOX levels are generally attributed to motors without EGR's. My question here, is what did GM do instead of the EGR to account for NOX levels. Does my car have a 3 way Catalytic Converter (if so, that could definetly be my problem). Other than that, are there any suggestions, past experiences people have with NOX levels; what they changed to reduce them?
There is something about lean air/fuel ratios, what could I do to account for this?
Any help is appreciated
IF YOU COULDNT READ THAT, ANY HELP WITH REDUCING NOX LEVELS IS APPRECIATED. BUT THE ABOVE IS WORTH THE READ.
Just to add to that:
Car was orginally purchased from Paul...who had it boosted.
The car has a 2.5 inch cat back system with a high flow cat and is about 2 yrs old or maybe more.
Emissions wise, on a NA car, is it better to have a high flow cat or just a stock cat? I would imagine the honey comb stuff in the high flow cat is ported with bigger holes then the stock cat. If that is the case then since the air flow ratio is NA wouldn't that cause the cat not to perform the same as stock....lowering emissions by letting exhaust gases pass through bigger openings??
Hopefully that made sense.
Damit I need an edit button...
I meant increasing emissions by letting exhaust gases pass through without proper filtering.
Freer flowing only affects power/performance. NOx is attributed to combustion temps being too high. Whatever you have for EGR ain't working right, or cooling system is lacking.
ANYMORE SUGGESTIONS...i m gonna fix it tommorow, changing the cat that is
NOX emissions can rise up if you're running an overly rich air/fuel mixture. One notorious culprit for running rich is a bad or failing O2 sensor. I had a very similar problem (passed emissions except for NOX) and it turned out to be a bad O2 sensor (at the exhaust manifold for my car). Cheap and easy fix, even if it doesn't cure the problem 100%.
If the car was previously boosted, was anything in the fuel system upgraded too? If there are oversized injectors, for example, with the now N/A engine, you may have problems getting a proper air/fuel mixture (especially at idle).
I'd replace the O2 sensor(s) first, then start looking at other A/F ratio modifiers such as fuel injectors and MAP sensor.
If this is an all-the-sudden problem, it's probably not your cat. Even a completely bad cat doesn't go out right away - it takes a while. Plus, a bad cat (bad kitty!) typically causes slightly higher than acceptable emissions, not a through-the-roof NOX test failure. In some states, you can pass emissions tests with no cat at all.
Check out my ride at CarDomain.com
