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all NSXs pass california smog test?

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Yep its a 50 State car :wink:
 
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I'm having problems smogging a stock out-of-state 98 NSX. the HC count is between 57-71, which is way higher than the allowed maximum count. I thought all stock NSX should pass CA smog test with flying colors. is this not correct?
 
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Did you make sure that you got your cats nice and hot before taking it in for the test? A cold or bad cat can cause high HC readings.
 
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I drove around for about 30 mins before the smog test. I suspect that because the seller used 87 gas once on the way to california on this past saturday, that might cause problems.
 
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High HC is caused by poor combustion. Meaning that unburned fuel is exiting the exhaust. Normally, the cat will take care of whatever remains unburned. However, if there's a lot of fuel that is leaving the combustion chamber unburned, some of it will likely still make it out the tailpipe and cause high HC readings.

If you warmed up your cats before the test (and didn't let it cool down while waiting), other possibilities include bad spark and maybe bad oxygen sensors.
 
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Yea, tried heating up the cat before the test...didnt work...the Acura dealership said that a bad cat is a possible cause but the ECU should pick that up...ECU check was clean. The car has low mileage (28k for a 98 NSX) so i suspect some buildup is present in the engine. So C-foam was used in an attempt to clean it out. However, that didnt work. Now, the Acura dealership will replace the plug wires, hoping it will fix the problem.
 
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Did you fail the HC test at the lower RPM or the higher RPM? If at the lower RPM, then I would suspect cats not warm/hot.

Is your car going onto the rollers immediatley after getting to the smog station? Even waiting 10-15 minutes lets the cats cool enough to cause higher HC readings. Happened in my NSX and Integra before. Solved the problem by driving around the block, warming the cats again and driving right up onto the rollers (no waiting).

Did you have them turn the TCS off before running the test (also turn off climate control).
Did you do the other checks - clean air filter, clean spark plugs, clean throttle body. These are all DIY types of operations.
 
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the Acura dealership will replace the plug wires

While they're at it, you might ask them to check the flux capacitors too.

Listen to the advice you're getting here. Drive the car 30 minutes and keep it running before the test starts to keep the cats hot. It'll pass.
 
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Listen to the advice you're getting here. Drive the car 30 minutes and keep it running before the test starts to keep the cats hot. It'll pass.

Everytime I take my OBD-I 94 for smog it is a funny drama. The technician struggles mightily to figure out a place to keep the RPM pickup thing. He ends up adjusting it some 10 times. To make it worse I never take notes and always forget where the last best location was :-(. Once that is done, I need to convince him to keep the car running for like 5-10 minutes before even attempting the smog testing.

The last time, it failed with a hgh HC count. I made him keep the car running for a while on the dyno and then redo it and it passed. He insisted that other than burning gas it would do nothing. Was left shaking his head when it did pass :).

I did replace my O2 sensors right after that, My gas mileage in city driving went up from 19.5 mpg to 21.4-22mpg after the O2 sensor change. So something was suboptimal with my old O2 sensors. I am hoping that I will pass smog easy the next time.

So. Get it nice and hot before smog. If that fails, replace O2 sensors and then go for the smog test.

-vamsi
 
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Everytime I take my OBD-I 94 for smog it is a funny drama. The technician struggles mightily to figure out a place to keep the RPM pickup thing. He ends up adjusting it some 10 times. To make it worse I never take notes and always forget where the last best location was :-(. Once that is done, I need to convince him to keep the car running for like 5-10 minutes before even attempting the smog testing.

The last time, it failed with a hgh HC count. I made him keep the car running for a while on the dyno and then redo it and it passed. He insisted that other than burning gas it would do nothing. Was left shaking his head when it did pass :).

I did replace my O2 sensors right after that, My gas mileage in city driving went up from 19.5 mpg to 21.4-22mpg after the O2 sensor change. So something was suboptimal with my old O2 sensors. I am hoping that I will pass smog easy the next time.

So. Get it nice and hot before smog. If that fails, replace O2 sensors and then go for the smog test.

-vamsi

You can pick up the RPM from the battery.

As for the O2 sensors, I think it is worthwhile to replace them if they are over 10 yrs old. You can get the NGK for about $110 from sparkplug.com
 
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I need to smog mine pretty soon. The last time the smog guy took the coil covers off and had trouble picking up the RPMs ...it dropped out and failed the test 3 times. I was relieved when it passed with flying colors on the 4th attempt. I felt bad because I used a coupon and only had to pay $29 so I tipped the guy $10. I was not aware of the battery idea.
 
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How do you get RPM off a battery? I've only ever seen the inductive sensor, which has a pretty good range.

On '91-94 NSX bad cats will never pop a code, since there is no secondary O2 to measure cat efficiency. O2 sensors will pop a code if they're completely dead or open circuit, but they can lose sensitivity or be off, which the ECU can't distinguish as being bad.

Between O2s and cats, the O2s have a much more dramatic impact on HC readings. Both need to be hot to work right. The O2s are responsible for telling the ECU how much gas to feed the engine to match the air coming in. If it's not hot enough to work then the ECU defaults to a safe (rich) program.

If the O2s are working right, then the fuel going in gets matched up with O2, and about 98% of the fuel is combusted in the cylinder. The other 2% gets expelled without burning (not mixed well enough), along with enough O2 (also unburned) to oxidize the fuel. This is important, because cats cannot convert unburned fuel without O2 present in the exhaust. This is why some cars have air pumps--to add O2 to the exhaust gas to help oxidize unburned fuel on the cats. If there is no air pump, then cats can't reduce any excess fuel that isin't matched with excess O2.

One possible contributing factor to HC count is that you have a single O2 sensor that is measuring 3 cylinders. What if 2 are rich and 1 is lean, or vice versa? The ECU can only do so much.

If the car is running well the cats are hardly needed. There was a recent post about a NSX with high flow cats passing smog in CA. It was running well.
 
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the car is still not passing smog. This is what i have tried:

replace airfilter with a new one
C-foam
new spark plugs wires
Drive it around for at least 30 mins before the test.
Keep the car running and rev it right before the test.
turn off TCS

Acura says O2 sensors are ok, no timing problem and gaskets are fine (no leaks).

I'm frustrated and baffled right now. I dont know what's wrong with it. Will this cause more problems in the future?

I'm buying this car from a seller who is out-of-state. He drove the car to california so that we can smog it but it has been 4 days and countless tests and the car still not passing smog. I'm waiting to have the car passes smog before i give him anymore money than my deposit of $5000. I'm concerned about the reliability of this car. Is this problem typical for NSX?
 
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It sounds like this car has a lot of carbon buildup...I wouldn't let the car sit and idle for long periods of time prior to the test. That will just contribute to the problem. What most people do is run the car in higher rpm ranges for extended lengths of time to get the cats nice and HOT and then try to smog it as soon as you get the car to the smog shop.

Other than that, as others have suggested a Throttle Body service may be warranted. I am surprised that the car won't pass. I have not heard of this happening very often. Maybe the spark plugs are bad also.

Best of Luck to you!
 
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the car is still not passing smog. This is what i have tried:

new spark plugs wires

In case you didn't catch kpond's sarcasm about the flux capacitor, the NSX is coil-on-plug. There are no spark plug wires. Hope they didn't charge much for them! I would have a different shop look at it.

Post up the smog numbers.
..........15MPH.............25MPH
HC........PPM................PPM
CO........PPM................PPM
NOx......PPM................PPM
 
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If you want to try and use a different place to pass PM me, the place I used is in Garden Grove. I just need to find my smog papers..
 
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smog numbers slightly varies but this is one instance.
..........15MPH.............25MPH
HC........61................41
CO.......0.02................0.01
NOx......58................45

I've tried a few different places, including a pre-test at Acura.
 
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smog numbers slightly varies but this is one instance.
..........15MPH.............25MPH
HC........61................41
CO.......0.02................0.01
NOx......58................45

I've tried a few different places, including a pre-test at Acura.

What's the pass criteria for those numbers? HC might be a bit high, but not terribly. The others are great.
 
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Go ahead and post up the %O2 and %CO2 numbers. It may be something simple, but I wouldn't buy a car that was failing smog till after the problem was resolved.
 
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...............%02.......%C02
15 mph ......0...........15.3
25 mph ......0...........15.3

Yea, I'm not going to buy the car unless it passes smog. It's up to the seller to get it pass smog.

what do you think? what can it be? What is causing high HC?
 
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