Failed Smog need help

[sgvnsxrated]

I took my car to the test only station today and failed smog. Here are the numbers;

HC:
15mph 13 (max 114)
25mph 15 (max 88)

CO:

15mph 0.01 (max 0.73)
25mph 0.01 (max 0.61)

NO:
15mph 1038 (max 785)
25mph 495 (max 724)

Technician went halfway during the test and said it wasn't looking good, so he suggested to drive it hard for a couple miles and come back, after a little bit of fun, came back and retested and failed. He suggested that maybe the EGR valve was clogged, which I'll probably have checked right away. Any other suggestion you guys have that can help make sure I pass next time??

BTW, I have a 91 w/ 81k miles. Completely stock except for a Comptech exhaust which I don't think affected the outcome.

 

[ckarate2]

n0x is a by product of heat.
have some one look at the o2 sensors.
your not getting enough o2 in the exhaust.
if yhou unplug one injector it will create a vaccuum pump effect in the motor which will cause the motor to run lean which in turn puts more o2 int he exhaust system which in turn brings down the nox levels that you have failed on.
think about a piston moving up and down.
if there is no fuel in the cylinder than the piston moving up and down is pumping air. more air in the cylinder will lower the nox levels in the cats. which is what they are monotering. the c0 and co2 levels will drop- also.
have the o2 sensors and egr valve looked at closely and check to see if the valves and injectors are not a little carboned up;
ky
chris

 

[Daedalus]

If you unplug an injector you'll also get a CEL, which will cause a fail on the smog test anyway. The O2 is OK. If there was too little O2 you would have much higher CO (not enough O2 to form CO2, so CO is made instead).
You can pull a vacuum on the EGR and see if the engine runs rough. If it does, then it isn't clogged.
Check your temp sensor resistance to make sure it's OK. If it were to read cold the ECU might not turn on the EGR or the fan (was it running during the 15mph test?)
Possibly the thermostat is bad, though they usually fail open, not closed, and you passed at 25mph. (cats not hot enough at 15?).

 

[Briank]

Oxides of nitrogen are formed when the combustion temperatures get high enough to oxidize the Nitrogen in the air. By adding exhaust "EGR" to the intake the temperature is reduced there by reducing the amount of NO. I would guess you have a partially clogged ERG valve or exhaust passage.

 

[sgvnsxrated]

Thank you for all the great feedback. One of the reasons I love prime. I'll remove my EGR tomorrow and check it out. Any suggestions on how to clean it out?

 

[Hugh]

Any suggestions?

Get the hell out of California. :biggrin:

 

[BD]

Talk to NSXSUPRA, he will help you.

 

[sgvnsxrated]

Get the hell out of California. :biggrin:

no kidding. Some of the cons of living in so cali are beginning to outweigh the pros. These emissions tests are getting so strict soon they'll start passing laws on bean and burrito intake.

I seen a 2 bed 1.5 bath 900sq ft home in my neighborhood (not even a great neighborhood) go on sale today for almost $700k.

 

[Skorpion]

On the positive note a emission test can also tell you what can also be wrong with your car with the diagnostics. If your car was running right it would pass. If there is something wrong, you can weed out down the failing parts on the car.

 

[sgvnsxrated]

I removed the EGR valve today, as well as the metal tube that goes across it. that thing was dirty. I sprayed it down with carb cleaner brushed it out, and tried to get as much as I could in the chambers. While I was at it I cleaned out the throttle body also and replaced the filter. I also noticed that my coolant level was low, I suspect I might need to give SOS's site a visit and pick up a new coolant tank. :biggrin:

After filling the coolant up and putting everything back together, I decided my engine was looking a lil dirty, so I degreased the whole engine compartment down with some Black Magic Engine shine. When I tried to start the engine, it took a couple cranks, I gave it a lil gas and VROOOM this huge cloud of black smoke come pouring out the exhausts. After a couple mins of idling it all cleared up.

 

[nis350]

I removed the EGR valve today, as well as the metal tube that goes across it. that thing was dirty. I sprayed it down with carb cleaner brushed it out, and tried to get as much as I could in the chambers. While I was at it I cleaned out the throttle body also and replaced the filter. I also noticed that my coolant level was low, I suspect I might need to give SOS's site a visit and pick up a new coolant tank. :biggrin:

After filling the coolant up and putting everything back together, I decided my engine was looking a lil dirty, so I degreased the whole engine compartment down with some Black Magic Engine shine. When I tried to start the engine, it took a couple cranks, I gave it a lil gas and VROOOM this huge cloud of black smoke come pouring out the exhausts. After a couple mins of idling it all cleared up.

So did it pass smog?

 

[sgvnsxrated]

So did it pass smog?

Not sure yet, I'll have to find some time this week to take it back to the smog check station.

 

[nsxsupra]

If it is not free to retest at your test only smog station. You might want to try Dynoxtreme to pass it legally.

http://www.dynoxtreme.com

They only do legal smog, if the car barely fails, they will try whatever necessary to get you pass, assuming all your mods are carb certified. Viper/Corvette/Supra/Skylines GT-Rs/Evo/RX-7/Imports love this place.

If you are heavily modified with absolute no hope of passing, then you will need alternative method. Its hassle free, doesn't even have to drop off the car, but it will cost you.

 

[nis350]

Not sure yet, I'll have to find some time this week to take it back to the smog check station.

how easy is it to remove and clean the EGR valve? Do you need to replace any gasket for reinstallation?

Does the car run better now that it is cleaned?

Thx. :wink:

 

[Red97T]

I failed smog last year - the solution was to run the car up & back to/from the shop on the freeway at high rpms. Passed on the second try.

Bob

 

[sgvnsxrated]

how easy is it to remove and clean the EGR valve? Do you need to replace any gasket for reinstallation?

Does the car run better now that it is cleaned?

Thx. :wink:

The removal of the EGR valve was simple. Just two 12mm bolts for the EGR itself, and 4 10mm bolts for the pipe that goes over it. All accessible without removing anything else. Gaskets should be replaced, which I didn't realize till after I already removed them, since i did it on a Sunday I wasn't able to get new ones. So I used a very small amount of silicone gasket stuff I got at Autozone. After I tightened everything up it looked good to go.

The acceleration on my car did feel much smoother. Not sure if it was from the EGR, me cleaning the throttle body, or if it was from replacing the air filter. My idle smoothened out a bit, and the car starts up faster.

 

[sgvnsxrated]

Finally found the time to take my car in for another smog check, would have done it sooner but I was working on the new double din stereo :biggrin:

Anyways....failure once again. I was able to bring the NO level down to 850ish. Shop recommended that I change the o2 sensors. Are these hard to change?

 

[zahntech]

The EGR port usualy plugs up where it opens up into the manifold ..if you got it completely cleaned out than you may be running too lean...lean mixtures make for exsess heat..your .01 CO is somewhat lean..check that EGR port opening into the manifold..then you will need to monitor the O2 sensor out put if EGR is not your issue...O2 sensors stuck in the rich voltage range will cause the ECU to run the motor lean in responce...you may also have a fuel system issue causing not enough fuel to get to the combustion chambers IE cloged fuel filter or dirty injectors...check the EGR port First..Good luck...JZ

 

[sgvnsxrated]

The EGR port usualy plugs up where it opens up into the manifold ..if you got it completely cleaned out than you may be running too lean...lean mixtures make for exsess heat..your .01 CO is somewhat lean..check that EGR port opening into the manifold..then you will need to monitor the O2 sensor out put if EGR is not your issue...O2 sensors stuck in the rich voltage range will cause the ECU to run the motor lean in responce...you may also have a fuel system issue causing not enough fuel to get to the combustion chambers IE cloged fuel filter or dirty injectors...check the EGR port First..Good luck...JZ

I'll remove the egr once again and try

 

[zahntech]

The motor should run very rough and possibly die with the EGR removed..if it just runs a little rough or normaly at idle, the port is restricted or completely pluged....JZ

 

[skafia]

I just smogged my 1991 NSX and it failed the first time. The previous owner told me that I needed to run the car very hard for 15 minutes on the freeway so it is really hot. I did that, proceeded to the smog check station and it passed just fine.

 

[sgvnsxrated]

I just smogged my 1991 NSX and it failed the first time. The previous owner told me that I needed to run the car very hard for 15 minutes on the freeway so it is really hot. I did that, proceeded to the smog check station and it passed just fine.

I drove the car for an hour on the freeway going average 65-75mph right before testing. Nothing hard, but the smog check station let my car idle for a good 5-10 mins. Maybe I didn't run it hard enough? Or maybe it cooled down too much?

 

[skafia]

Going 65-75 MPH in what gear? In 5th or in 3rd? Hehe... You have to keep the engine revs up and tell the smog place to throw it right on, don't let it idle there.

BTW my results are extremely similar to yours. Failed the 15MPH test. I also threw in some octane booster if that helped.

 

[nis350]

I just smogged my 1991 NSX and it failed the first time. The previous owner told me that I needed to run the car very hard for 15 minutes on the freeway so it is really hot. I did that, proceeded to the smog check station and it passed just fine.

Would you post the before and after number?

I have a feeling that he may end up replacing the cats to pass. Hope that is not the case.

 

[sgvnsxrated]

5th gear. I'll try again next saturday. I purchased new o2 sensors which I'll install this week, and i'll check the EGR again. I also bought some RXP gas kicker. From other forums I heard it helps pass emissions. For $8 can't hurt to try.