Is your NSX failing smog? Read this.

goldNSX said:

Thanks for the update. Changing oil brings HC down a little bit but by not very much. I still think you have minimal leak somewhere as HC is low at 2500 rpm and high at idle. Maybe worth checking for leaks in the air system. What about the injectors seals?

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I think u might be right. I do have some vacuum rerouting as i have NA2 valve covers on my NA1 engine. Ill check the lines when i have time. I pulled the injectors about 5 years ago and had RC eng service them and i put new seals in at that time.

Rdx injectors going in soon so fresh seals will be in. Ill do an e test again next year in the fall and we will see how the idle is with fresh gas and clean air cleaner.

This is for Canada smog? California need to run on a dyno machine and it may not pass with these number. My car have 125k miles. I did everything on this post and still failed. I just replaced 2 aftermarket cats and it passed with good number. Paid $450 installed.

lithiumus said:

Been 2 years since i replied and never went for an e test till this year. Ive done a lot which likely contributed to the now low numbers however my idle still has somewhat high HC.

While I did a lot of things, its more likely that the IAT sensor is what allowed the car to pass. I write this siting at the DMV waiting to get my renewal stickers!

My 2500 rpm results were
HC Limit = 200, Reading = 25, Pass
CO Limit = 1, Reading = 0.01, Pass
Dillution = 12.55

Idle results were
HC Limit = 200, Reading = 170, Pass
CO Limit = 1, Reading = 0.02, Pass
Dillution = 12.77

I did go into the Etest with 8+ month old fuel mixed with probably older fuel from before and a dirty air filter. I was certain I wasnt going to pass so I didnt bother burning off the 3/4 tank of fuel and forgot to clean the air filter. I suspect the 170 HC number might get better if I had fresh fuel and clean air filter.

What has been done...

- oil change
- spark plugs
- IAT sensor replacement

Plugs were pretty fouled from before. Could be due to rich idle. I was getting 600-800 HC readings when i was failing.

Actually the IAT sensor didnt seem too bad. Some oil on it but not really that gummed up...

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what kind of aftermarket cats did you install? Are they direct bolt on?

ac011 said:

This is for Canada smog? California need to run on a dyno machine and it may not pass with these number. My car have 125k miles. I did everything on this post and still failed. I just replaced 2 aftermarket cats and it passed with good number. Paid $450 installed.

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They are cut and welding into the oem cats. It can still be uninstall with the oem bolts.

ac011 said:

They are cut and welding into the oem cats. It can still be uninstall with the oem bolts.

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What brand cats? Looks like your in Northern Ca. Is that right? My car is due next month for its check.
I have not really followed it, but I am not sure there are any non OEM Ca. legal aftermarket CATS? Does anyone know of any? Just in case? Thanks

These look to be direct bolt on? Any experience with the installation as well as the effectiveness to pass smog?

mandrewz said:

http://www.oscaroparts.com/d-e-c-catalytic-converter-1993-acura-nsx-20023-5808-44531-egt

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nis350 said:

These look to be direct bolt on? Any experience with the installation as well as the effectiveness to pass smog?

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I would order a set if I had more info. CARB info etc. Not much info on the site?

As I just did the AIT Sensor cleaning, I thought I might do a short write up on it because maybe someone wants to know exactly how to do it.

What you need:
Set of allen key
Sockets 8mm and 10mm
Philips screw driver (bigger one)
Hammer

1) remove the plastic cover that goes over the fuel rail of the front 3 cylinders. (2 screws, 8mm socket)
2) remove the Honda/Acura name Plate on top of the intake manifold (2 screws, allen key)
3) remove the intake manifold cover (4 screws, 10mm socket)

Now you can see the sensor. Its mounted to the manifold with two philips type screws.



I borrowed this picture from another thread here on prime. You can see the exact location of the sensor. Its on the middle runner on top of the fuel rail (which is not installed on that picture)

4) Take a perfectly fitting philips screw driver (it really needs to sit tight in the head of the screw), put it onto the screw and give it some taps (not too hard) with the hammer. This will loosen the threads of the screw, making it easy to remove and also prevent the aluminium thread from getting stripped.

5) repeat that on the second screw, unplug the cable and remove the sensor.

Clean it with brake cleaner or whatever you have on hand.

6) Put it back together the other way around. Be careful when tightening the philips screws. They do not need more torque than you can apply with a normal screwdriver.

I did not drive yet but my NA1 did not have any problems like bad smog but sometimes a little hesitation directly after cold start and would not fire up immediately after sitting for a week.

The sensor was not as bad as seen on some of the pictures here but still had carbon residue and little bit of oil on it. Cleaned up easily, no rubbing required.

I did test start it and it may be a placebo effect but I think it started better. It still did not like the first throttle input but the second was ok. I will have to change the fuel filter, spark plugs and give it a bottle of injection system cleaning additive combined with a nice tank of highest quality premium unicorn Shell VPower fuel I can get here in Austria.

Bernhard

This is a great thread! I tried to do this but one of the screws is proving almost impossible to remove even with PB Blaster. Any tips?

Try an impact tool with a tight fitting impact slot head. The impact should break it loose.

lithiumus said:

Try an impact tool with a tight fitting impact slot head. The impact should break it loose.

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OMG didn't know such a tool existed... thanks for the tip. Amazon here I come.

You can get impact bits that are slot, philips, robinson... Made of the same chromoly bdenum that impact sockets are made of. Standard chrome bits will break/shatter, these bits will just bend if its completely seized. That little slot screw will pop right off with a little impact!

Awesome thread. My 1991 failed smog last time and for the first time- very aggravating. Especially after changing the oxygen sensors, changing plugs, cleaning the air filter, cleaning the throttle body, etc. Hope this little task works. It took me all of 10 minutes to pull the sensor and wipe off the dirt and oil. You guys rock!

I'm gonna miss this site as my NSX has just sold. For the time being, I'll be a car guy with no car. : (

YellowHaze said:

Awesome thread. My 1991 failed smog last time and for the first time- very aggravating. Especially after changing the oxygen sensors, changing plugs, cleaning the air filter, cleaning the throttle body, etc. Hope this little task works. It took me all of 10 minutes to pull the sensor and wipe off the dirt and oil. You guys rock!

I'm gonna miss this site as my NSX has just sold. For the time being, I'll be a car guy with no car. : (

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I successfully passed smog test today and not by much. Not sure if it was due to having cleaned the sensor or not. Us California car owners have it tough. One of the owners of the smog shop said most NSX owners don't drive their cars enough. She said it's like a person not getting enough exercise and becoming unhealthy. Perhaps it's due to deposits that dry out and get hard from non-use. Just a guess. So, one more reason to get behind the wheel of these awesome cars and move the odometer some. :smile:

after two years installed my aftermarket cats, it passed again today. Make sure you tell the tech to use first and second gear ONLY.



- - - Updated - - -

Apparently some people use an inline resistor to bypass the cats - http://zero-signal.org/o2/O2bypass.html.htm
I found another article by an Audi tech that described a different procedure.

Just thought I'd echo that this worked for me. My car passed Ontario's Drive Clean in 2014, HC was close to the limit though so I was a bit nervous about it going in today. I took the IAT sensor our and it definitely had some grime on it, nothing like the bad pics I've seen but I gave it a wipe down with brake cleaner. Car was barely warmed up, on old gas (sat from Nov-May) and it passed with flying colours!

Great tip.

This might make a good sticky for 91-94's.

After 12 yrs of ownership in Ca. ....... Finally figured it out. (Ronnie at Irvine auto repair actually)
Highly recommended if you live in the area you get your NSX smog there. 91-94 specifically.
My cars issue was a lazy EGR valve. And its by design. For cold start ups.
Most 91-94 NSX's according to Ronnie have this issue. And it can drive you & the smog guys nuts.
Even after replacing my EGR valve 4 yrs ago It was still hit and miss.
The solution for me (And other NSX's he tests is to make sure the EGR valve is operating & open prior to running the test.
Past 1st time. Old gas, have not driven the car much over the past 2 yrs. (few hundred miles maybe)
No more driving the hell out of it getting it hot, silly $$ race gas, magic potions, new plugs, cats, replacing all sorts of things prior to getting a smog test.
Mystery solved. For me anyway. Just give Ronnie a call if you need more details.

so there is a way to force the egr to stay open during the test?

No. If there is I'm not sure how.

so how did he get it open for your car to pass?

MCM said:

No. If there is I'm not sure how.

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He ran the car & could tell. "Just give Ronnie a call if you need more details"

According to the last tech who tested my NSX (which passed with elevated NOX), it's usually not the EGR valve (mine was OK), but the tube the gasses go through. He suggested reaming it out to get rid of the gunk.
But for sure clean the IAT.

Its my understanding its not a bad EGR valve, but rather when it gets its signal to open. Lower RPM's? Not so much...
Higher RPM's, no problem. It may have been designed this way for cold starts / low rpm use. Its like night and day watching the screen while its on the dyno. But it might just be my car. And the other NSX's tested at that shop.