# High NO at 15mph - everything else is normal on Acura **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [January 30, 2019, 7:09pm UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626 "2019-01-30T19:09:19Z")\ **Posts on this page:** 19\ **Page:** 3
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [February 16, 2019, 3:07am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/41 "2019-02-16T03:07:45Z")
It is inside the braces for all years, **25mph 8** 2019 **25mph 646** 2019 retest ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [February 16, 2019, 3:14am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/42 "2019-02-16T03:14:28Z")
It seems a mystery remains. The nox problem seemed to switch from 15 mph to 25 mph on the retest. That actually makes more sense to have nigher nox at higher mph, have to wonder if the first test data got switched inadvertently by the testing place. In any event you are golden for 2 more years, and have found some good ideas to try before your next required testing then. I wish the state of Calif (I presume this is Calif) could be more helpful in things like this, but I guess their mission is to test the car, not help the owner. You got the re-test done for free, right? ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [February 16, 2019, 3:40am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/43 "2019-02-16T03:40:51Z")
Test data is machine to computer - so its impossible Retest is supposedly free but costed me $3-4 more - I never asked for explanation nor examined the receipt. My thinking is the gas still has Cataclean additive in it (I only drove 20 miles) - when this is fully used it will come lover to the original level. Had the NOx at 15mph is still higher at 400, I would have had retarded the ignition timing - but it returned to 2005 level. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [February 16, 2019, 3:47am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/44 "2019-02-16T03:47:41Z")
> [@George\_San\_Jose1](#): > > Congrats on a diagnosis job well done. What was the diagnoses? I haven’t been following this. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [February 16, 2019, 3:58am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/45 "2019-02-16T03:58:10Z")
The diagnosis was the engine wasn’t heated up properly prior to emissions testing the first time. > [@sciconf](#): > > Test data is machine to computer - so its impossible Good point. Getting the car to the testing mph is done by the emissions tester pressing on the gas pedal and watching the speedo presumably, but the computer must also know what the mph is b/c the wheels are rolling on a treadmill that is presumably connected to the computer. > [@sciconf](#): > > $3-4 more - I never asked for explanation nor examined the receipt. That’s probably the state fee for some paperwork involved. They don’t assess it until you pass. I get that fee too, but if it takes two tests, only after passing the 2nd. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [February 16, 2019, 4:08am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/46 "2019-02-16T04:08:32Z")
> [@George\_San\_Jose1](#): > > The diagnosis was the engine wasn’t heated up properly prior to emissions testing the first time. A cold engine shouldn’t produce excessive amounts of oxides of nitrogen. Sounded to me like the catalyst wasn’t hot enough. Driving in second gear for 3 miles probably “lit” the catalytic converter to burn off years of granny driving residue. ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [February 16, 2019, 4:10am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/47 "2019-02-16T04:10:47Z")
Yeah it is California ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [February 16, 2019, 4:26am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/48 "2019-02-16T04:26:59Z")
> [@Nevada\_545](#): > > Sounded to me like the catalyst wasn’t hot enough. Driving in second gear for 3 miles probably “lit” the catalytic converter to burn off years of granny driving residue. Is this good or bad - I am unsure what you are saying? ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [February 16, 2019, 4:28am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/49 "2019-02-16T04:28:44Z")
> [@George\_San\_Jose1](#): > > It seems a mystery remains. Yeap, Historical values - highest ever: 34 72 78 44 34 8 646 ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [February 16, 2019, 4:33am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/50 "2019-02-16T04:33:04Z")
If you had presented this test as the original problem, high nox at 25 mph, nox ok at 15 mph, I’d be leaning towards a cat on its way out. Suggest to monitor the intake manifold vacuum at idle going forward. If it starts creeping up, cat may be plugging up. ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [February 16, 2019, 5:07am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/51 "2019-02-16T05:07:37Z")
> [@George\_San\_Jose1](#): > > If you had presented this test as the original problem, high nox at 25 mph, nox ok at 15 mph, I’d be leaning towards a cat on its way out. Suggest to monitor the intake manifold vacuum at idle going forward. If it starts creeping up, cat may be plugging up. Cataclean additive is not making anything worse right? ---
**Author:** ![jtsanders](https://avatars.discourse-cdn.com/v4/letter/j/c2a13f/32.png) [@jtsanders](https://community.cartalk.com/u/jtsanders)\ **Post date:** [February 16, 2019, 2:42pm UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/52 "2019-02-16T14:42:31Z")
If you drove the car the same way before the test for all those years, that alone might explain the difference. What is the maximum level for NOx in Cali at 25 mph? I’m also skeptical about the Cataclean product. I suppose you pour it into the gas tank, and it must burn when it passes through the cylinder. Darned few, if any, solvents would make it through an explosion like that unburned. If it actually does work, then it may not have completely cleaned the catalytic converter. ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [February 16, 2019, 6:18pm UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/53 "2019-02-16T18:18:51Z")
> [@jtsanders](#): > > If you drove the car the same way before the test for all those years, that alone might explain the difference. I am wondering what are u trying to convey? Yeah, all these yrs, I never cared about SMOG testing. I am also waiting for @Nevada_545 to clarify me. > [@jtsanders](#): > > What is the maximum level for NOx in Cali at 25 mph? Around 750 but the AVE is around 70. > [@jtsanders](#): > > If it actually does work, then it may not have completely cleaned the catalytic converter Well, there is a huge difference in the NOx level at 15mph - it went back 2005 level - then the car had under 40k mileage. Without a re-test, current result is in-conclusive. BTW, can u do unofficial SMOG in California? If so, after about 1000miles, I wish to test for SMOG and see. ---
**Author:** ![Honda-Blackbird](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/honda-blackbird/32/3159_2.png) [@Honda-Blackbird](https://community.cartalk.com/u/Honda-Blackbird)\ **Post date:** [February 16, 2019, 6:28pm UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/54 "2019-02-16T18:28:31Z")
I thought that carbon buildup on top of the pistons can help contribute to excess NO emissions. I believe this is true…and something that isn’t too difficult to try and clean up, just for giggles. I have found that a simple water injection system T’d into the brake booster vacume line or some other vacume entry… A small valve to adjust flow rate and a container like a pickle jar is all that is really needed. I used to do this on engines when I was a kid, just for fun and it worked wonders for cleaning the tops of the pistons I can assure you… I never tested for NO before or after but, I believe it would affect that specific output of that substance and since you seem to be just over the line with that…the clean piston idea may just nudge you into the passing lane so to speak. Just a thought and possibly a fun science project to boot! ---
**Author:** ![jtsanders](https://avatars.discourse-cdn.com/v4/letter/j/c2a13f/32.png) [@jtsanders](https://community.cartalk.com/u/jtsanders)\ **Post date:** [February 16, 2019, 7:33pm UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/55 "2019-02-16T19:33:08Z")
> [@sciconf](#): > > I am wondering what are u trying to convey? Yeah, all these yrs If you drove the same short time period to all the tests you documented and only increased the time before the last test, that might account for the change in 25 mph results. You don’t know how the increased warmup affects your smog test results until you do it. ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [February 18, 2019, 4:30am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/56 "2019-02-18T04:30:35Z")
A mechanic tells me that the increased NOx at 25mph is indication that the combustion is better due to better air flow. In this thread @shanonia stated that the (exceptionally) dark engine oil is due to dirty air filter - factory says every 30k miles - this was in there for 35k - I forgot about it - it was really dirty: [Mobil 1 5W30: Annual Protection Vs Extended Performance Vs Advanced full synthetic](https://community.cartalk.com/t/mobil-1-5w30-annual-protection-vs-extended-performance-vs-advanced-full-synthetic/134378/3) Had it been really warmed up, it would have still passed. For the next SMOG, I would for sure use Redline and really warm up the car. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [February 20, 2019, 3:23am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/57 "2019-02-20T03:23:46Z")
> [@sciconf](#): > > A mechanic tells me that the increased NOx at 25mph is indication that the combustion is better due to better air flow. I would have guessed the explanation to be more simple: NOX is more at 25 than 15 mph b/c there’s more volumetric exhaust flow going through the engine for the cat to process at 25 mph than 15 mph. > [@sciconf](#): > > dirty air filter Just to add some extra confusion, the last time my Corolla got tested for emissions, about a year ago, I did everything else I usually do, plugs, change oil etc, but I forgot to change the air filter. It passed with lower emissions numbers than it ever has since they started with the treadmill testing 15-20 years ago. ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [February 20, 2019, 3:31am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/58 "2019-02-20T03:31:41Z")
> [@George\_San\_Jose1](#): > > Just to add some extra confusion, the last time my Corolla got tested for emissions, about a year ago, I did everything else I usually do, plugs, change oil etc, but I forgot to change the air filter. It passed with lower emissions numbers than it ever has since they started with the treadmill testing 15-20 years ago. Oh, its validating the theory than confusing in my mind. Dirty air filter → less air → less combustion → lower emission #s So keeping a dirty air filter but warmed up engine/CAT will give lower emission values - a way to pass SMOG? ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [February 20, 2019, 3:36am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/59 "2019-02-20T03:36:02Z")
You might well be correct. When I realized about the air filter a little after passing, I replaced it, but kept the old dirty one for the next time I have to take the test … lol … [Previous page](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626.md?page=2)