So I'm not to fimiliar with the smog side of automotive. It WON'T pass the 15mph tests but PASSES the 25mph test no problem. It's to high on HC, CO and a GROSS POLLUTER on NO (Nox). The EGR valve was stuck closed but it freed itself when I manually pulled vacuum from it but I retested right after I did that. I replaced the o2 sensor but what else should I be looking at? Should I be looking at timing?

PS. car is a 94 Honda Prelude VTEC OBD1

EDIT**
After replacing some things and it didn't solve the problem, I had to remove the intake manifold and clean out the EGR Ports. After that, it finally PASSED with damn near ZERO Emissions.

 

I would look at timing, a possible miss, maybe do a tune up like plugs/wires/distributor, and I would also clean out the egr and all of its passages. Also make sure your using the right octane gas, and make absolutely sure that the car is warmed up.

 

Thanks for the reply. I did check the ignition timing earlier today and the ricer who owned this car before me ****ed with a lot of **** and it didn't look like they knew what they were doing. Today, I checked ignition timing and it was WAY to advanced probably causing detonation in thus causing WAY to much NOx. So I reset the ignition timing and re-adjusted idle speed. Gonna retest tomorrow, hopefully it gives me the Green light!!!! WISH ME LUCK!

 

Just my luck! After doing some adjustments, it passed the PRE-TEST but FAILED the actual test because the NOx barely went over. I'm gonna try cleaning out the injectors, intake system, retard the timing 3 or so degree, replace the spark plugs, coolant flush and run some G2P through the fuel system. Retest on Monday. This damn car is nickle and diming me to death.

 

For NOx you have to clean out the EGR system. Its what does most of the NOx control

 

Sounds like a bad cat.

 

so I just put a new cat convertor and an egr solenoid in, wish me luck. AGAIN...lol, should pass this time though.

 

Im having the same f'king problem. The last two smog test i passed (Last 4 years) and had my cat replace and all. Now my recent smog this feb, I failed. I replaced the EGR solenoid valve today, and **** failed smog even worse. WTF.

 

What were you failing? Which sections of the test? The standards are getting stricter each year, so you may pass one year but not the other.

 

Failing all now. Tremendously 4 times the limit on each category.

 

That's what was happening to me in the beginning so I replaced the o2 sensor, spark plugs and readjusted ignition timing. Everything went down a great amount to low readings. Have you tried those? Right now the only problem I am having is high NOx readings. My engine was kinda overheating but I have fixed the problem since the last smog pre-test. I also drilled out the EGR ports on the intake manfold runners and cleaned the build up out just to make sure I cover all the bases. I replaced the cat since my last post but it didn't do much. Should get the car back together by the beginning of next week so I'll keep ya posted.

I would definately replace the o2 sensor if you haven't already. Make sure you are getting the cat nice and hot before the smog.

 

If your failing Nox badly its one of a couple of things. Your overheating, your EGR system isnt working properly, or your timing is off, causing high combustion temperatures.As for the others, make sure your car gets fully warmed up before taking it for smog. You want to hear the radiator cooling fans turn on at least 2 times before taking it in.

 

Im actually gonna work on the cooling system today. Drain and replace the coolant/thermostat and the sensors. Had my fan switch sensor replace about 4 months ago. My timing is good. but i'll make it even better. If i can get a some intake manifold gaskets, take that apart and scrub that **** clean.

 

A faulty O2 or carbon build up can also raise NOx

 

Taking out and cleaning the intake manifold and EGR ports was a must. My intake manifold was cleaner than i thought but the EGR ports were f'king dirty and gunk up. I used 2 and half cans of carb cleaner to get it cleaned up. Sprayed it and let it sit, then dumped it. so much gunk. My EGR valve was super clogged. dirty also. Gonna put it back together tomorrow and re smog it monday.

 

True, forgot about those.

 

Bit the bullet and put a new O2 sensor in and then a new cat. Failed the 15mph test and pass the 25mph test. What else can cause high levels of NOx, timing is dead on to factory specs. no leaks in vacuum lines or bad sensors.

 

Try adding a few gallons of e85 to the tank.... or else leave the people's republic.

 

Will that affect it during the test? Heard of other people putting alcohol fuel becuase it burns cooler. Unfortunately EGR valve didn't help. Now it fails. Getting a new EGR valve today.

 

If your failing the NOx at the 15 its more than likely your EGR has a problem.

 

Check your ignition timing. remember to short the connector before checking it.

Also, egr valves don't go bad. They just get clogged up so that they don't work. All you gotta do is take it off and carb clean the hell out of it so that it moves freely when you push on the diaphragm. Removing intake manifolds and then engine brite-ing the hell out of them works best. I let mines sit soaked overnight for adding efficiency.

Ok, well, the egr valves probably do go bad but rarely.

 

They go bad more often that you think. They have a tendecy to leak. Slightest amount of leakage will reduce the amount of EGR entering the cylinders and will raise NOx.

 

After replacing some things and it didn't solve the problem, I had to remove the intake manifold and clean out the EGR Ports. After that, it finally PASSED with damn near ZERO emissions.

 

I had my buddys mechanic work on it. they did the same thing i did, just tore my EGR valve and intake manifold apart. Clean the **** out of it more and they got it to pass. took them a while to tinker with it but got it pass. They were frustrated that it took a lot longer to get it working correctly. but hey lets stress on me, and warranty included. NOx levels at 15 mph are low as hell. they Retarded the timing to 14BTDC also.

 

How far advanced was your timing?