This is my first post. I've been lurking for a few days now and browsing the archives. I just picked up an '89 Civic LX (4 door) to use as a daily driver. It's my first Honda. The car came from a high smog area so I took it to get CA's "enhanced smog" which is done on a dyno at different RPM. The car had fairly low CO and HC levels, in fact lower than 2 years ago based on an old smog invoice the PO included. It also passed the visual inspection. Unfortunately the NOx levels were too high and it failed. I've done my homework on this subject, but would appreciate any additional advice.

Correct me if i'm wrong, but apparently high NOx levels are caused by an out of tune car (not possible as this one has just had a full tune up sans dist. rotor), running too hot (not according to the gauge, also H20 pump and radiator are new), a faulty EGR valve (the owner's manual shows only automatic cars in CA having this part, car is a 5spd.), the last thing, and the one i'm suspecting is a bad cat. I'm pretty sure this is what it is, but am not positive. The cat is original I believe, with over 150k miles on it. Has anyone been through this before? Any advice? Am I on the right track to resolving this problem? I can get one welded in for about $165, but want to be sure before i do it.

My last question is in regards to a fluctuating idle. the owner's manual states the idle should be 750 rpm + or - 50. I'm experiencing an idle that fluctuates from about 450 - 750 rpm, staying around 500 most of the time. What is a possible cause of this? As stated above the car just had a full tune up (except for the ignition rotor). I'm also running 91 octane with techron.

Thanks!
-Oi-Punx

 

theres alot of scnerio for NOX
for example over advancing timing, carbon buildup, over heating,theres alot thing for nox to go up. nox is high temp on the engine. for your HC to go up your car may be experiencing misfire that way your HC is high.On your sheet can you gave me some numbers to look at.

 

Thanks for the reply. Here are the numbers

***15 MPH (1867 RPM) HC 95 PPM CO 0.19% NO 1197 PPM (Max allowed NO is 1001)

***25 MPH (2081 RPM) HC 84 PPM CO 0.25% NO 1032 PPM (Max allowed NO is 875)

It should also be noted that ignition timing was checked at B18. The car is 100% stock with no modifications.


[Modified by oi-punx, 8:05 PM 11/12/2002]

 

No need what so ever to run the high octane in your car. Down grade to 86. The 91 octane is for 10:1 compression and higher. Anything lower and you run the lower octane.

I suggest replacing the cat. Cleaning the trottle body and intake manifold.
And attempting to adjust your idle by adjusting the idle screw on the trottle body.

When you get ready to go to the smog station. Run the car for a while. Take the long way there and really lay into the gas to heat up the cat.
Once there leave the car running to prevent the cat from cooling down.

 

I live in San Diego, all my cars have always been modded, so yes I have been throught this before. I actually just had the same exact problem on my Montero trying to sell it. Replacing the cat will have very little effect on NOX, it will not get you down to passing anyways. However your CO shows your car is running lean and your CAT isn't doing that good of a job because your HC is a little high, and retarding the timing will make your HC higher. The key is timing! Retarding the timing will have a MAJOR effect on NOX, however to pass the visual inspection, they check the timing. This is at the discretion of the tech. If you have the money, and you just want to get this over w/ and not worry about becoming a gross polluter:
Replace the cat.
If you can't afford it here are some other tips:
Check your O2 sensor and replace if in doubt.
Buy some of the "pass or don't pay" stuff(it doesn't do what it says it will do, but it helps) use following instructions.
Retard your timing to the most retarded that spec allows.
Use the lowest octane fuel you can pump(87 here)
Make sure to run the car hard at WOT before you test, don't let it cool down(CATs only do their job when HOT.
Make sure they run the big fans up under your car to keep the temp down while doing the test.
All of these tips I learned the hard way, so I hope they help you. Good luck!

 

Thanks for the responses. This is good information. I want to get it registered within 10 days of purchase and i'd prefer not to mess with the timing. If the tech discovers that it's out of spec I could risk throwing away another $80. I don't mind spending money on a new cat, but I do mind spending money on a cat and then finding out that that's not the issue. Do you think that if I replaced the converter that it would pass? I'm confused.

I did not see them use fans when they smogged it, they might have, but I didn't see them. Also I used high octane because I was under the assumption that it would burn cleaner. I understand that it will burn more completely which would equate to running hotter (thereby increasing NOx). This is the first and last tank of high octane for this car.

 

Yes getting the new converter and cleaning the trottle body and Intake Manifold will pass.

 

If your factory spec for timing is 15 BTDC like mine, and yours is at 18, then my guess is that the timing is the main culprit. Factory spec allows +/- 2 so you could get away with 13 which would dramatically lower your NOX. But what I was getting at is that if you retard teh timing, it will raise your HC and it looks like you are cutting it close already. Adjusting the timing is very easy w/ a $30 timing light or you can rent one for free at AutoZone if you prefer. Definitely run 87 octane for the test though especially on a lower compression engine. If the place says that they can get it to pass for $50-75, what they will do is after you leave they will retard the timing til it passes, and punch in that it's at 15 and then tell you that they had to adjust some stuff. They did this to me, but I didn't care because I just wanted it to pass.