Failed my smog test, what to do next?

SoCalDude

SoCalDude

Experienced Member
Joined
22 March 2003
Messages
1,392
Location
West Los Angeles, CA, USA
So mine failed this time. Barely passed two years ago. Ran it real hot before the test, etc. but still didn't pass. The tech said that perhaps a new oxygen sensor might do the trick. Now what next? He also said I could take it to a smog repair and test type place so the repairs can be tested to make sure they make the car pass.

Has anyone done this? I can't imagine a test & repair smog place has even seen a NSX before let alone try to fix the smog on one. Dealerships generally don't test for smog either?

I'm in West LA if anyone has suggestions as to where to take it to. Thanks.
 
Do you have the numbers?

You could probably "borrow" someone's good CATs and/or O2 sensors to do the test that lives in LA. . .
 
Might be worth your while to have your o2 sensors replaced. Sparkplugs.com has a very good price on them compared to the stealership. How do your numbers look?

I know it's frustrating just wanting to get the car to pass but like you said, it'd be hard to trust any smog station with the NSX. Every time I take it to smog they have a hard time finding the engine. They always struggle to find a good wire to use for tach. They never know how to close the engine hatch properly. If they can't do those NSX specific things correctly then I wouldn't trust them to work on the car.

I'd take the car to a good mechanic like Ramon.
 
ryu said:
For us to help, a list of mods (or lack thereof) would be of great assistance
Click to expand...

CARB legal Comptech Headers and exhaust. Had them for years. This is the first time I can't get it to pass. I'll post the numbers tonight.
 
Last edited:
As Malibu stated, The O2s are the easiest to address first. I have a 91 with original cats and it passed with flying colors about 5 months ago but I did just go through a big maintenance service. One of them was changing to new OEM O2s. I'm on Top Speed headers but that matters little. I mentioned this because I can post my numbers if you need a comparison.

Are you burning any oil? Are you running rich or lean? As Adrian said, the numbers (CO2, NOx) will be helpful once you get them posted later.
 
Have you tried that liquid smog stuff, it is supposed to be guaranteed to get your car passed. I know it is hard to put weird stuff in the NSX but it helped me get an old '78 LUV truck through smog without replacing anything. It is an alcohol based product that oxidizes the fuel when it is burnt.
 
ryu said:
As Malibu stated, The O2s are the easiest to address first. I have a 91 with original cats and it passed with flying colors about 5 months ago but I did just go through a big maintenance service. One of them was changing to new OEM O2s. I'm on Top Speed headers but that matters little. I mentioned this because I can post my numbers if you need a comparison.

Are you burning any oil? Are you running rich or lean? As Adrian said, the numbers (CO2, NOx) will be helpful once you get them posted later.
Click to expand...

Not burning any oil. Not sure about rich or lean. Here are my numbers.

NSXSmogTest.jpg
 
ss_md said:
Have you tried that liquid smog stuff, it is supposed to be guaranteed to get your car passed. I know it is hard to put weird stuff in the NSX but it helped me get an old '78 LUV truck through smog without replacing anything. It is an alcohol based product that oxidizes the fuel when it is burnt.
Click to expand...

Never heard of it. Is it called Liquid Smog?
 
It's called "Guarantee to Pass" made by CNC. You can buy it at Autozone for $10 bucks. It comes in a blue box, with a bottle inside.

I just failed smog myself. My NOx was 100 over the max on 25 mph. The NOx on 15mph was high also but passed. Everything else was very low.
 
Car is running super rich. Cats are not the problem. There is no O2 left to reduce the HC. You can put a bandaid on it, but the car's not running right.
 
Last edited:
Malibu Rapper said:
Might be worth your while to have your o2 sensors replaced. Sparkplugs.com has a very good price on them compared to the stealership.
Click to expand...

If you replace your O2 sensors make sure you do so with exact OEM replacement sensors. I have read that many Honda's and other brands are finicky with the sensors and will trigger a CEL. Whether or not this is true with the NSX I do not know, but IMO why take a chance.
 
ss_md said:
If you replace your O2 sensors make sure you do so with exact OEM replacement sensors. I have read that many Honda's and other brands are finicky with the sensors and will trigger a CEL. Whether or not this is true with the NSX I do not know, but IMO why take a chance.
Click to expand...

Who makes the oem sensors? Denso, NKG, etc?
 
ss_md said:
If you replace your O2 sensors make sure you do so with exact OEM replacement sensors. I have read that many Honda's and other brands are finicky with the sensors and will trigger a CEL. Whether or not this is true with the NSX I do not know, but IMO why take a chance.
Click to expand...

I forgot who tipped me to the sparkplugs.com but I owe him a thanks. I bought the NGK OE Identical O2 sensor and that thing looks identical to the real thing.

On my OBDII car, I would go through up to all 4 O2 sensors a year replaced on warranty by Acura by OEM O2 sensors. I haven't had any of the replacements go out yet, knock on wood.
 
easiest thing for you to do is to replace the O2s. it's unlikely that all of your plugs would foul out but i would check that out also. I would also do a cleaning of the throttle body and wherever the MAP/MAF sensor is on our cars. I haven't had to go into this area of the NSX so I don't know.

In other cars that have your problem, I would clean out the MAF and change the O2s.

rant: I wish my Prime email notifications would work again :frown::frown::frown:
 
If you are worried about the time to get this done, don't be.

FYI - If you pay the registration on time, but do not complete the smog the DMV will hold your new sticker until the smog check is completed.
 
ss_md said:
.....FYI - If you pay the registration on time, but do not complete the smog the DMV will hold your new sticker until the smog check is completed.
Click to expand...

+1


What most people dun realize is that if you get pulled over and paid ur registration on time, even if you don't have the smog taken care of at the same time, the police won't usually ticket or tow the car.

It's happened to me 4 times on other cars.
 
I paid the DMV already. I maybe taking a trip to see Ramon on Friday.
 
Don't mean to throw another variable to the mix but if the coils or one coil is not functioning right (weak, etc) would it be possible that a it's not giving out enough spark output to cleanly burn all the fuel?

And maybe the more likely scenario would be that several are weak so the spark is not cleanly burning all the fuel in several cylinders. I'd hate for you to test this out but if you are changing the plugs anyway and someone has a spare set of coils, it might be worth a try...

Why this is more apparent in lower RPMs I can't exactly say...
 
Malibu Rapper said:
Remember sparkplugs.com if you have to replace the O2 sensors. They are about $200 a pop from Acura/Honda. About 1/4th that price from sparkplugs.com and they look identical. Ramon replaced mine last time, too. Good luck!
Click to expand...

Did you buy yours and bring them to Ramon and did he pick them up for you?
 
Just spoke to Ramon. He thinks the cats are the problem. He suggested I borrow some oem ones to pass. He said the aftermarket ones don't work well. He's also booked up for several weeks so I can't drop the car off with him right now.

How hard is it to put on a set (one or two)?
 

Similar threads

A
1991 NSX just doesnt want to run right/pass smog...
Replies
24
Views
2K
Honcho
Honcho
jsullyboy
Low Engine Power before 4k RPM
Replies
11
Views
196
jsullyboy
jsullyboy
W
NSX Hugo Window Regulator Instruction Clarification
Replies
4
Views
108
Wild Turkey
Wild Turkey
Heineken
Amplifier Quadruplet Repair
Replies
8
Views
486
Heineken
Heineken
N
Emission / Smog test failed, O2 passed / Air Fuel failed.
Replies
1
Views
841
Old Guy
Old Guy
Back
Top