failed smog

digitaldrifter91 · Mar 3, 2006

car: 1986 300zx non turbo v6 3.0 w/126k

hehe well i barley failed. im wondering i can get some assistance from you guys. I have done a tune up

replacing the spark plugs a few months back
distribitor cap and rotor
NEW oem spark plug wires
NEW MSD blaster SS coil
cleaned engine with throttle body cleaner
ran fuel treatment
new cat 2 years ago
ran ecu codes to find i get a normal reading. (no codes)

air filter is clean and i replaced like 90% of the vaccumn lines in the engine bay.

15 MPH test:

co2-12.72
02-2.77

HC (max/meas)
128/168

Co% (max/meas)
.80/.59

No (max/meas)
1106/1686

25mph test:

Co2-13.40
o2-2.10

HC (max/meas)
103/75

Co% (max/meas)
.60/.29

No (max/Meas)
936/738

basically i failed on the 15mph test on the Hydrdocarbon, and the No levels. **** soo close though.

so if anyone can help let me know. yes i drove the car for about 15 minutes, also raced to 90 mph hehe

chrome · Mar 3, 2006

High HC would point to a lazy or faulty oxygen sensor. Have you changed the O2 sensor before? These things have a finite life, just like a spark plug. High NO levels would point to an inoperative EGR system.

tom slick · Mar 3, 2006

Check out these websites to learn what all this stuff means
http://www.autoshop101.com/forms/h55.pdf
http://www.autoshop101.com/forms/h56.pdf

digitaldrifter91 · Mar 3, 2006

i never replaced the o2 sensor, i looked around for one, no one has it but the dealer at about 97 bucks.

i will probably change that 02 sensor. i was looking back at older smog tests and when i had the cat replaced, the results were near the same as now but in passing range. oddly the stock cat was wayy lower, in some emmisions.

do you think if i just change the 02 sensor that everythign will go down? or would i have to take out my egr valve and clean it out?

Vilan · Mar 3, 2006

What Chrome said.

You can probably get an O2 sensor for cheaper if you look online, but if you're not sure how to install it you may want to let the dealer do that anyway, so...

Your car doesn't burn oil, does it? That would be boosting your HC. Taking a look at the EGR would be good but they seem to be quite a pain to clean out properly, at least on my car.

got boost? · Mar 3, 2006

yeah I would replace the O2 sensor, i think the '86 had a different o2 sensor than the other years (same as '87-'89 turbo), so it may be hard to find aftermarket. you can take the o2 sensor out and test it fairly easily, google "test oxygen sensor".

andyd · Mar 3, 2006

An O2 sensor is an O2 sensor. I balked at paying 110$ for the specced O2 4 wire sensor for my 88 528e. I bought a 45$ 3 wire specced for a Ford 5l. The 4th wire is just a drain, I hose clamped it to the housing and butt spliced the leads to the old sensor's connectors. Works fine. A little research can save you some money.

Gary Allan · Mar 3, 2006

In 30 sec I found three potential O2 sensors, all for under $60 (as low as $47.xx).

What about these doesn't work?

Fatboymoe · Mar 3, 2006

One thing I always do before a smog check is to make sure my vehicle is at operating temp. I usually run it down the freeway for at least 10 miles and try to run it at high RPM's.

Another possible problem is that your carbon canister is saturated with fuel. This can cause high H/C readings if the solenoid opens the return to the throttle body during the test.

digitaldrifter91 · Mar 5, 2006

you know what ****** me off...2 years ago when it didnt pass for some odd reason, is that the old cat put out very low numbers, after they changed the cat and welded the thing in there the numbers were at a barley pass limit...

it didnt pass cuase the timming was off and my dad wasnt thinking so he took it to a smog and repair place. it was the timming that was read wrong.

so lets say the hc was at 168 now..before it was at like 60 and the No reading was at 1686 where the old cat was at like 450...

now tell me, that raises some concern and i didnt notice it till now that happend. im wondering if i should call the company but it may be too late??

[ March 09, 2006, 01:33 AM: Message edited by: 59 Vetteman ]

GMGuy · Mar 6, 2006

Did you get the car good and hot before going for your test? I have always (but once, and it showed) taken at least a 20 minute highway drive before my test and try to time my arrival at the shop as close to my scheduled time as possible to keep the cats hot.
There is a "warmup" cycle on the dyno in our e-tests before the actual test begins, however, having watched a handheld exhasut analyzer on my car I know my cats take a lot longer than the scheduled time to get up to temperature and start doing their job, once they hit temperature the readings drop like a stone.
The one time I didn't take my full pre-drive I barely squeeked by the test (I go to the same place for all my e-tests). My last test with a full highway jaunt prior passed again with lots of room to spare. No changes to any emmisions equipment except pcv valve for at least the last 7 years, along with what appears to be the orginal 1989 catalytic converters-just fresh oil, fuel & air filters, plugs, wires, cap&rotor.

Alex.

digitaldrifter91 · Mar 8, 2006

well i havent done anything, im getting a new catco cat tomorrow and new rear "b" piping...they have holes in it.

i tried to remove my egr valve today and man that sucker is on soo tight!!! im going to turn the timming down to 20 degrees (spec 20+-3)

if it dont pass after the new cat...then im taking it to this guy who said he can pass it.

i may just purchase a new oxygen sensor as well.

robbobster · Mar 9, 2006

Aftermarket cats don't last as long as factory ones.

But only two years...are you sure it's bad?

got boost? · Mar 9, 2006

I would definitely start throwing parts at it, sounds like a geat idea.

digitaldrifter91 · Mar 9, 2006

it was just weird how right after the new cat was put in and tested 2 years ago the numbers went sky high.

for the o2 sensor i have a choice....OEM one is 95 dollars, aftermarket bosch is 99 dollars...

oem i can get in 3 days, bosch i can get tomorrow...what you guys think???

got my new b piping, sounds alot quieter thanks to no more big huge holes, and a new cat. but i really think i should change the o2 sensor...

got boost? · Mar 10, 2006

I told you before to test the old one.

robbobster · Mar 10, 2006

Also, are you certain they put the correct cat in?

Not sure about the older cars...but there are difference between an OBDI and OBDII cat (I've been told that OBDII cats have more rhodium, for example).

digitaldrifter91 · Mar 13, 2006

well finally passed.

had a new cat put in, and new rear piping to my exaust, that cost me like 220.

then changed the 02 sensor, found the correct one for my z and passed.

the old o2 sensor was black as ****. lol.

passed with flying colors.

failed smog

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