Not passing smog. Suggestions appreciated

[Esteves]

My daily driver vehicle isn't passing smog. It's a 1978 Datsun 280Z. It only drives about 6 miles round trip when I do use it and sometimes I won't use it for 2 weeks straight.

I've pasted the last three smog tests that were done to it.

03-27-04 - Vehicle Mileage: 270925

The vehicle didn't pass smog. It was due to a bad catalytic converter (it was the original one) so I should be happy it lasted this long. It was replaced.

04-07-04 - Vehicle Mileage: 270979

Vehicle has new catalytic converter and it passes with no problems.

06-09-04 - Vehicle Mileage: 273108 (2129 miles later)

Vehicle doesn't pass smog this time. The only different between now and the previous one is the tank is full of 91 octane fuel (normally, I put 87 octane). This station is a different station from the previous two.

The vehicle is fuel injected (if anyone is wondering). The vehicle was driven 20 minutes prior to showing up to the station and when I got there, I was instructed to drive right into the test bay, so I was tested immediately.

Since my vehicle is so old, I can only go to smog test only centers and repairs need to be done somewhere else. Since I failed, I get one free re-test - so I need to try to track the problem down.

My guess might be O2 sensor, but since the vehicle isn't driven far, it never gets a chance to warm up, so I could have carbon build up as well.

Any other suggestions/clues/ideas would be appreciated.

Below are three previous smog results.

<img src="http://www.bimmerfest.com/forums/attachment.php?attachmentid=78027&d=1150137308">

[Ed]

I'm no pro at this but I think that a 20 minute drive before the test is not enough to warm everything up. Also unless your running a high compression engine the 91 octane will not burn completely. 87 or lower is your friend here.

Also I'm not sure which state your in but you should always take your car to a place that will do a pre-test. This is where they test the vehicle's emmisions without sending the results to the DMV.

[Virto]

I'm assuming you're in California, or at least you have a california car, based on the cat.

You'll want to drive the car for at least half an hour, and doing some highway speeds wouldn't hurt.

Like Ed says, you may want to find a place that you can take it to test for a small fee, it's better than the state getting in your business. You'll want to fill with the lower octane fuel before testing, and whatever you do, don't run some kind of carbon cleaner. If you have a lot of buildup it can break chunks free and damage the engine or create false readings.

[Walter Moore]

It looks like the car only failed on CO%, and that by just a little. Could it just need a tune up? Getting the engine hotter might bring the CO level down a little. But like Ed, I am no expert.

No, I take that back. It was nearly twice the limit on the latest 15MPH test... Is the air injection pump for the converter working? (does it even have one of those? I have never looked at the emissions systems on a FI Z car.)

[EScanlon]

With only 2k miles in two years, at an average of 6 mi. per ROUND trip.....that is 3 miles in the morning, 3 in the afternoon, DEFINITELY nowhere near enough time to warm up the engine adequately at any time.

You might even have a plugged Cat. Converter which did NOT get better with a 20 minute warmup.

I'll leave the rest to the proper Mechanical Guru's, but IMO you need to take the car out for a SERIOUS drive every once in a while. Heck, you might even consider taking the LOOOONG way to work. Not only will you enjoy the drive more, but you'll do your car a world of good.

A car that doesn't get driven much is sometimes MORE problematic than one that gets regular and moderate distance put on it.

FWIW

E

[beandip]

Escanlon is right you may have plugged the new cat. As others have said before use some regular grade gas , take the car out on a hi way an punch it . Drive it at hi way speed at least and take it for a ride for a hour or so if you can , at speed. This may blow out some carbon and may heat the cat so it can do it's job . Hopefully . The hardest thing on a engine is to keep running it with out warming it completely . You never get the engine up to proper heat and moisture condenses inside the block , sulfuric acid is formed and it will destroy the engine . It takes about 20 to 30 minutes to completely bring the engine and oil to temp. The temp gage will show normal a long time before the block and oil is actually at temp .

[sblake01]

From the results, I'd say that you're running too rich based on the CO readings, except for that one test which shows the CO incredibly low. Too rich will eventually kill the cat. If all sensors are good (throttle switch, temp sensor, cold start valve, etc.) then you might look at adjustment of the air flow meter. It's a rather tedious task to get that adjustment just right. Take a look at this article.

http://www.atlanticz.ca/zclub/techtips/afm/index.html

[Esteves]

Yes, it's in California.

I appreciate all the suggestions. The long way to work is a 60 mile one way trip and my knees and ankle will only let me work the clutch so long before they tire out (hence public transportation is my friend).

I'll take it for a long run this weekend and see about burning all that 91 octane fuel.

Should I be checking the O2 sensor? I noticed that back in 2004, it looks like the smog station checked my O2 sensor because it says I passed, but the one in 2006 shows NA for O2 sensor.

Thanks for the suggestions and keep them coming.

[mdbrandy]

Yes, it's in California.

Should I be checking the O2 sensor? I noticed that back in 2004, it looks like the smog station checked my O2 sensor because it says I passed, but the one in 2006 shows NA for O2 sensor.

Thanks for the suggestions and keep them coming.

\

A '78 280Z does not have an O2 sensor. They were introduced with the 280ZX. (I have a '78 280 - california version with CAT, and no O2 sensor).

[Esteves]

Thanks for the heads up on that regarding the O2 sensor.

[sblake01]

Taking it for a long drive does not cure the problem. You're running too rich. Besides not passing smog, you're killing your catalytic converter. You need to adjust your air flow meter or have it done by someone who knows how. He'll put it on an exhaust analyzer and adjust until the CO is within spec. Take it from someone who has two cars with this system and has never failed a smog check with either of them. Not only will you pass smog but your car will run better and you won't have to replace the cat as often. The one in my 78 has been in it since I bought the car in 1997. It's CO reading was 0.12 and 0.01 on last year's test.

[sblake01]

Just curious, the date you listed for the thrid test is a typo, right? Shoud be 06-09-06 rather than 06-09-04? So it had been two years between passing and failing. I thought that, based on the posted dates, that it had only been two months and hence, my answer. Anyway, I would try a good tune up including a new PCV valve and even an oil change before taking on the the AFM adjustment. Contaminated oil can raise the CO level since its vented into the intake through the PCV valve.