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Originally Posted by sil80phobia
Just figured someone might find this useful.
So my 95 S14 failed smog last week, just BARELY. Bone stock except for Injen CAI. My car is EXTREMELY clean and well maintained, so it pissed me off.
Max allowable NOX was around ~700/736 ppm for idle/25mph tests. I was testing 710/745 .. just a hairs breadth from passing. Based on my calculations, I only needed a ~2% improvement to pass.
1. first thing I did was inspect the EGR setup. Not surprised to find the lower EGR vacuum line rotting. (pretty common as I've searched). So that and the FPR line was replaced with silicon tubing in short order
2. I had timing at 20.3 degrees when it failed. They allow +/- 2 degrees so I backed timing down to 18 degrees.
3. I unplugged a vacuum line and ran an entire can of intake/throttle body cleaner through the engine at 3000 rpm.
4. Drove around a week with a bottle of guaranteed to pass in the gastank (with 91 octane as I've read it helps lower NOX) for a week.
5. overinflated the rear tires to minimize load on the dyno. also had less than an 1/8 of a tank of gas and I emptied my trunk and took out my spare - not sure any of this did anything, but someone had suggested it - anything to get me that 2% margin I needed to pass!
6. changed my oil.. was due anyway.. all in the name of minimizing load on the engine..
7. drove the piss out of the car for about 20 min (nice sustained 5k RPM canyon run) prior to testing
The results blew me away. I was hoping for a 2% improvement on my previous 710/745 result. What I pulled off today was 77/92 !!! thats right.. 77/92, not a typo. Essentially 30 min of my time and $10 in stuff. Didn't touch my 02 sensor, left my original 165k mile cat on.
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hehehe, you figured out my little secret for making what would be a gross polluter pass. In fact I had a test only car that came up gross polluter. I took it home and basically did a variation on what you did above, without putting any fuel additive in the tank. I took it back the next day and it passed so clean, the smog tech asked me what I do for a living, hahahhahaha, he was convinced I was a pro mechanic.