I have a 1997 z24 5 speed that failed nox on my smog test at the 15mph test it was at 859 when limit is 450 or something like that my rpm was 1750 . but it passed the 25mph test it was like 150 under the limit . the cat test good the 02 sensor is about 1 month old . the egr valve is working . do you think if I put new egr valve it would fix the problem ? or is there something I can add to my fuel to lower the combustion temp ? can not adjust timming . past the hc and co with no problem and there was only like 0.5 02 so my is ok even the smog said the cat looks good .
Try Seafoaming it first then add a quart of denatured alcohol from Home Depot in the tank then retest. Worked for me in Arizona. Doug in P.R.
92 Pontiac Sunbird LE, 2.0, AT, Red / Black with Grey 155K miles. Hurricane Maria Survivor ! ( It takes a licking and keeps on ticking ! ).....in Salinas, Puerto Rico!
I cleaned the egr out and I used methanol . I put about 1 gallon in with a haft tank of gas and that's how I got though my smog test ,
. Doug in P.R.
92 Pontiac Sunbird LE, 2.0, AT, Red / Black with Grey 155K miles. Hurricane Maria Survivor ! ( It takes a licking and keeps on ticking ! ).....in Salinas, Puerto Rico!
You probably already know this but you should get the engine hot (like at least a 10 minute highway drive) before doing the smog test. Several years ago one of my (2) 1996 2.4L Cavalier convertibles failed CA smog. (Nox, IIRC). The technician told me to take it for a 10-minute highway drive and to bring it back. It passed. Apparently the cats work better when they're hot. Now I always drive at least 10 minutes down the highway before getting a smog test.
If you find a solution, please let us know what it was. I'd like to keep my 2.4L 1996 Cavalier convertibles for many years to come, but I live in fear of failing CA smog and having to sell them out-of-state.
in ct i just tuned out the check engine codes. the only way to fix cali is to drop it in the ocean... that being said let the car get warm. before the test i used to have to do 30m so the systems said they were ready
Ya I know the cat was hot and the shop would hold the engine at 2500 rpm for about 5 min. before testing . using methanol cools the cylinder temp so it can lower nox
