Failed Emissions Test

[GreatWhiteNorth]

Hi,

I took my '91 NSX in to my local dealer last evening to perform an emissions test for my plate renewal. The HC reading exceeded the limit of 78 ppm ( it measured 133 ppm ) at 2525 rpm but passed under idle conditions.

When I purchased my NSX from another dealer last spring, it past the same emissions test by a wide margin. Back then, the HC reading was only 16 ppm but the NSX had the original exhaust manifold and muffler installed back then. Since then, I've installed the DC Sports headers and cat-back exhaust but retained the original cats. Could the new exhaust system be the cause of the higher HC levels? Has anyone also experienced problems passing their emissions test with aftermarket headers/exhaust?

Can anyone offer advise on ways to troubleshoot the cause of the high HC levels?

 

[nsxtasy]

Did they make sure the engine was nice and HOT before they ran the tests?

 

[0260n3]

I am about to get a smog for the 91' that I just purchased in the southern cal area, can anyone help me understand the smog process, where why would it be better to run the car hot in order to pass the test? (same thing the smog station told me how they would do it)

If i do fail, what is the repair cost that I should expect and on what parts? I am a non-techy when it comes to car parts, so please keep the terminologies simple

thanks so much,

 

[NSXrebel]

like nsxtasy said, make sure your engine is hot. going for a nice "spirited" drive should take care of it. from my personal experience, most of the time its the catylic converter that goes bad. I don't know how much they cost for the NSX but it should help out alot especially if it still has the original one in there.

 

[GreatWhiteNorth]

Unfortunately, I was not present at the time of the test nor did I think to mention it.

Typically, how long does the engine need to be operating before the test. Are we talking a couple minutes ( from cold start ) of idle time or do I need to go for highway drive for an hour before bringing it in for the test.

 

[SexyRed]

Mine failed too with little driving. Drive the car hard and let idle while waiting for smog. It passed.

 

[nsxtasy]

Originally posted by GreatWhiteNorth:
Typically, how long does the engine need to be operating before the test. Are we talking a couple minutes ( from cold start ) of idle time or do I need to go for highway drive for an hour before bringing it in for the test.

It needs to get up to operating temperature. A couple of minutes of idling is not enough. I live 3-4 minutes from my local testing station but I make sure to drive the car at least 10, preferably 15 minutes; if I need to drive it at slow speeds on local roads to get there, I keep it in first or second gear to keep the revs up and get the engine nice and hot.

 

[robr]

just fyi, even with NO cats, this car does fine. id be happy to find my emissions readings if you're interested in the measurements. on my 300zxtt which was near impossible to get to pass, it seemed it was always an oxygen sensor that was shot.

 

[GreatWhiteNorth]

I spoke with the service manager this afternoon and he said their policy is to drive the test vehicle around the block or to let it idle for 3-4 minutes before subjecting the vehicle to the test. I've made arrangements to have it tested again tomorrow morning at 8:00am sharp. I go for a nice long drive and arrive just in time for the test. Hopefully that will be enough to get me by this time.

The service manager mentioned the problem may also be a faulty O2 sensor. The shop that installed my headers may have damaged it while removing it from the OEM exhaust.

In the worse case scenario, the cats may have deteriated significantly due to prolonged track use.

 

[Tobal]

I just had my Emmissions test yesterday and i failed. Somehow mine is the opposite at Some throttle they actually brought my HC down to a good steady level, but while at Idle, the car ran to like 200 something HC. What could be the problem? They ran my car really hot just to get the HC down at the 2500rpm check.

note: i do have the DC Sport exhaust

 

[lemansnsx]

Originally posted by Tobal:
I just had my Emmissions test yesterday and i failed. Somehow mine is the opposite at Some throttle they actually brought my HC down to a good steady level, but while at Idle, the car ran to like 200 something HC. What could be the problem? They ran my car really hot just to get the HC down at the 2500rpm check.

note: i do have the DC Sport exhaust

1. DC Sport exhaust should not affect emissions.
2. Does your temperature gauge read normally? Thermostat is connected to EGR system - if thermostat is not opening then chances are that the EGR valve is not opening either.
3. High HC readings are typical of a problem with the EGR system - clogged passages, inoperative solenoid, etc. You'll need to have the dealer check this out.


------------------
Andrew Henderson
The NSX Model List Page

"We have long acknowledged that enthusiasm for things automotive is a sure
sign of emotional instability if not outright dementia" - Brock Yates