Is your NSX failing smog? Read this.
- Thread starter johnnymo
- Start date
Yes, and thats the problem..... It was not designed to open when the testers want it to open.
Any temp, any rpm range.
It can be seen on the screen by the tester. Changes the numbers dramatically.
Any temp, any rpm range.
It can be seen on the screen by the tester. Changes the numbers dramatically.
Not a full test to check if its opening. Once it gets the signal to open, it stays open through the test.
As I understand it, its like a cold start feature in the ecu. But am no expert..........
Ronnie at Irvine auto repair can fill you in. This had even Ramon scratching his head. (yrs ago)
(The best NSX mech in SoCal by far = Ramon) Good luck. And am glad my posts helped a couple folks here anyway.
Will be doing it all again next summer myself... Cant wait...........
As I understand it, its like a cold start feature in the ecu. But am no expert..........
Ronnie at Irvine auto repair can fill you in. This had even Ramon scratching his head. (yrs ago)
(The best NSX mech in SoCal by far = Ramon) Good luck. And am glad my posts helped a couple folks here anyway.
Will be doing it all again next summer myself... Cant wait...........
The EGR valve is controlled by a map in the ECU which opens the valve under a specific set of RPM and engine intake manifold pressure (MAP) conditions. The EGR opens under mid engine load conditions and adds exhaust gas into the intake manifold to dilute the air & fuel mix which reduces the combustion temperature and reduces NOX. The EGR does not open at low RPM or low engine loads and does not open at high engine loads. The testing conundrum is that the engine speed and load have to be high enough that the engine has entered the area of the ECU map where it commands the valve open. The fact that some cars seem to pass the NO limits just fine says to me that this should not be a problem; however, I note that in some of the test results the engine RPM for the 25 mph test are significantly different suggesting that the cars have not been tested in the same gear.
If the EGR valve or the associated EGR passages are plugged up this will reduce the amount of exhaust gas entering the intake which will result in higher NO. This problem may not be detected by the ECU because the EGR valve may still be going fully open and the ECU only monitors the position of the valve.
The cats need to be replenished with oxygen in order to do their job which is done by having the engine oscillate above and below a 14.7 AFR at a rate of about once per second (or faster). It might be possible that if the O2 sensors are slightly off (they commonly fail by reading lean) the cat is not getting the required dose of O2 which would degrade its performance. However, it would be a fine line between an O2 sensor that is off enough to impair the cat; but, not off far enough to trigger an error code.
I don't think there is a temperature related factor for EGR operation (other than it may be blocked if the ECU/Engine is still in warm up mode). The catalytic converters definitely have a temperature related performance issue - hotter being better up to a point. The 2000 and later cars which have the aux air pump that fires air directly into the exhaust manifold during cold starts may have a testing advantage because the additional air mixed with additional fuel at start up is specifically designed to bring the cats up to operating temperature quickly. Of course, no amount of fiddling with the EGR valve is going to bring you into NO compliance if your cats are shot.
If the EGR valve or the associated EGR passages are plugged up this will reduce the amount of exhaust gas entering the intake which will result in higher NO. This problem may not be detected by the ECU because the EGR valve may still be going fully open and the ECU only monitors the position of the valve.
The cats need to be replenished with oxygen in order to do their job which is done by having the engine oscillate above and below a 14.7 AFR at a rate of about once per second (or faster). It might be possible that if the O2 sensors are slightly off (they commonly fail by reading lean) the cat is not getting the required dose of O2 which would degrade its performance. However, it would be a fine line between an O2 sensor that is off enough to impair the cat; but, not off far enough to trigger an error code.
I don't think there is a temperature related factor for EGR operation (other than it may be blocked if the ECU/Engine is still in warm up mode). The catalytic converters definitely have a temperature related performance issue - hotter being better up to a point. The 2000 and later cars which have the aux air pump that fires air directly into the exhaust manifold during cold starts may have a testing advantage because the additional air mixed with additional fuel at start up is specifically designed to bring the cats up to operating temperature quickly. Of course, no amount of fiddling with the EGR valve is going to bring you into NO compliance if your cats are shot.
After reading the detail post from 'Old Guy' and your test results from Irvine, I'd bet the reason your car did better was that he used 1st gear for 15mph test and 2nd gear for the 25mph test. I recalled mine was 2nd for 15mph and 3rd for 25mph. The lower gear in your test put a lighter load on the engine (less pollutant), and the higher RPM probably caused the EGR valve to open.
Thanks 'Old Guy' for the information.
Thanks 'Old Guy' for the information.
Not a full test to check if its opening. Once it gets the signal to open, it stays open through the test.
As I understand it, its like a cold start feature in the ecu. But am no expert..........
Ronnie at Irvine auto repair can fill you in. This had even Ramon scratching his head. (yrs ago)
(The best NSX mech in SoCal by far = Ramon) Good luck. And am glad my posts helped a couple folks here anyway.
Will be doing it all again next summer myself... Cant wait...........
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Thanks for the info here. I had high idle HCs (but still passing) and found this. Apparently cleaning the IAT once every 26 years or so is a good idea.
Cheers. PS, the screws used to fasten it are actually JIS fasteners. A JIS screwdriver takes them out with very little difficulty.
Cheers. PS, the screws used to fasten it are actually JIS fasteners. A JIS screwdriver takes them out with very little difficulty.
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- 19 September 2003
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Ronnie / Irvine Auto Center does it again
Required to smog my '94 with CTSC again (last time was 2019, see my post above). Returned to Ronnie at Irvine Auto Center and he took great care of me and the car. Test was passed with flying colors (it's a CLEAN motor even at 137k miles and with CTSC!!!) and I'm set for another 2 years of fun motoring in SoCal. If you need an NSX smogged in SoCal, strongly suggest you take it to Irvine Auto Center!
Required to smog my '94 with CTSC again (last time was 2019, see my post above). Returned to Ronnie at Irvine Auto Center and he took great care of me and the car. Test was passed with flying colors (it's a CLEAN motor even at 137k miles and with CTSC!!!) and I'm set for another 2 years of fun motoring in SoCal. If you need an NSX smogged in SoCal, strongly suggest you take it to Irvine Auto Center!
5 years now and my 97 CT car will not hook up to CA smog tester. Two monitors are not ready; emissions are good. CA now only allows one monitor not ready. Everyone and his mother has had a go at troubleshooting it including Ramon who recently did some extended maintenance on the car; Ronny at Irvine smog, just about everybody except for the CA referee. The 2 monitors that do not set are EVAP monitor and O2 Sensor monitor. The O2 sensors have all been replaced with new ones, two of them twice. The EVAP system has been checked and double checked. I have done more than 1,000 miles of "drives" in different configurations and sequences as suggested by dozens of people, everything short of cooking a chicken on the engine cover to no avail. I am always willing to listen......
long shot....check your IAT sensor ....it maybe needs to be cleaned.
This an important little sensor.
Bram
This an important little sensor.
Bram
I did that too, in fact replaced it with a new one. Thanks
My 1991 NSX with 58k miles failed smog on NOx at 25 mph in third gear. All other numbers were passing, especially HC and CO.
I'm convinced that third gear, reducing rpm to 1800 at 25 mph, was the problem. I'm pretty sure 1800 rpm was not sufficient for the EGR to open. Also the cats were not warm enough when I parked the car, and I had very old gas with stabilizer in it. After the first test I burned three tanks of gas on some fun driving with 2 Lucas bigger (30-gallon) bottles and one bottle of RxP. The car ran perfectly the entire time. Then I went to a different smog shop farther away with hot hot cats. This shop ran both 15 and 25 mph tests in second gear. My 25 mph NOx which had been about 600 on the first test dropped to 100, the lowest I've ever seen on this car.
I believe that California tightened the pass/fail thresholds based on results of tests taken in second gear, but then they changed the test format to require third gear at 25 mph. After seeing several years of perfectly functioning cars failing in third gear, California will probably loosen the threshold at 25 mph. In the meantime, find someone who will leave it in second gear. In second gear your 25 mph rpm will be about 2500 which is more than enough to open a properly functioning EGR. Just observe, don't ask. If you ask, you potentially convert an honest oversight to an infraction by the tester. Another option: If the tester can't figure out how to turn off the traction control, he will need to run a no-load (non-dyno) tailpipe test, which a properly running NSX will pass easily.
I'm pretty sure I've created more air pollution getting smog tests than I've ever saved by improving emissions. I'm certain that I've put more CO2 in the air by getting smog tests. That doesn't account at all for the money and time spent. Smogging a post-2000 car by interrogating the OBD2 system is, by comparison, a cost-effective breeze. If only the authorities would stop insisting that 30 year old cars run cleaner than new.
I'm convinced that third gear, reducing rpm to 1800 at 25 mph, was the problem. I'm pretty sure 1800 rpm was not sufficient for the EGR to open. Also the cats were not warm enough when I parked the car, and I had very old gas with stabilizer in it. After the first test I burned three tanks of gas on some fun driving with 2 Lucas bigger (30-gallon) bottles and one bottle of RxP. The car ran perfectly the entire time. Then I went to a different smog shop farther away with hot hot cats. This shop ran both 15 and 25 mph tests in second gear. My 25 mph NOx which had been about 600 on the first test dropped to 100, the lowest I've ever seen on this car.
I believe that California tightened the pass/fail thresholds based on results of tests taken in second gear, but then they changed the test format to require third gear at 25 mph. After seeing several years of perfectly functioning cars failing in third gear, California will probably loosen the threshold at 25 mph. In the meantime, find someone who will leave it in second gear. In second gear your 25 mph rpm will be about 2500 which is more than enough to open a properly functioning EGR. Just observe, don't ask. If you ask, you potentially convert an honest oversight to an infraction by the tester. Another option: If the tester can't figure out how to turn off the traction control, he will need to run a no-load (non-dyno) tailpipe test, which a properly running NSX will pass easily.
I'm pretty sure I've created more air pollution getting smog tests than I've ever saved by improving emissions. I'm certain that I've put more CO2 in the air by getting smog tests. That doesn't account at all for the money and time spent. Smogging a post-2000 car by interrogating the OBD2 system is, by comparison, a cost-effective breeze. If only the authorities would stop insisting that 30 year old cars run cleaner than new.
My box-stock ’93 with 193,000 miles failed—then ultimately passed—its California smog test. Here’s how:
Thanks for the suggestion, everyone!
- FIRST TEST: Passed everything except both NO tests.
- 15 mph: 797 (697 is limit)--FAILED
- 25 mph: 725 (724 is limit) )--FAILED
- SECOND TEST: Put in Cataclean (available on Amazon) per tester’s recommendation. A couple weeks later, drove at about 4000 rpm for the last few minutes going to the smog-check place. Both improved and I passed the 25 mph test:
- 15 mph: 745--FAILED
- 25 mph: 672--PASSED
- THIRD TEST: Put in second bottle of Cataclean. A couple weeks after that, removed and cleaned AIT sensor as described above. Before test, drove car on freeway for twenty minutes, maintaining about 5000 rpm by driving in third gear. At smog-test place, there was a ten-minute wait. Five minutes beforehand, I drove car down the street in first gear—5000 rpm--for five minutes. They rolled it onto the test stand. Results:
- 15 mph: 582--PASSED
- 25 mph: 480—PASSED
Thanks for the suggestion, everyone!
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