failed smog, question time (long)

[sammyg2]

My basilcally stock 1980 SC failed smog today three times. I had to take it to a test only station.

I leaned the mixture just a little tiny bit before I went the first time, I drove it around long enough to get it up to full temperature.

failed on excessive CO, reading was 2.75%, almost twice what is allowed. HC was a little higher than average but well below max.

I took it to Steve's independant Porsche shop, he put it on the smog tester and leaned it out some more until the CO read .18%

Back to the test only station, failed again on CO, this time at 2.4%

This car passed easily two years ago and at the time I had the O2 sensor disconnected.
So, I went home, disconnected the O2 sensor and leaned it out some more until it started to idle slightly rough.
back to the smog station, same results, almost identical readings.

I went back home and let it cool down for a while and then changed the O2 sensor with a known good spare I had. The car started right up but the idle settled down at around 550 and rough.
It had cooled down but was not stone cold.
I drove it for 5 miles, after a minute or so the idle came back up to around 850 and it ran smooth.

My wild a$$ guess is that the O2 sensor was partially bad, and that I might have a slight vacuum leak at idle. that would explain why it runs clean at idle but not at 2500 rpm on the rollers. The O2 sensor would explain why the idle came back up, maybe it was running real lean at idle and after the O2 sensor warmed up it made the necessary adjustments. Does that make any sense or am I way off base?

I plan to change the oil and air filter before re-testing again even though they have very low miles on them, probably plugs at the same time.
Any other suggestions before I have it tested for the 4th time? Anyone?

This is getting expensive and I can't wait to get everything re-adjusted to where I like it.
This is where I would normally say that living in Kalifornia sucks, but it's 85 degrees outside right now. Maybe it only sux a little

[nostatic]

Originally posted by sammyg2
This is where I would normally say that living in Kalifornia sucks, but it's 85 degrees outside right now. Maybe it only sux a little

My son and I were at the beach from 1pm until sunset yesterday. In swimsuit and t-shirt.

It sucked *very* little at that point in time.

[juanbenae]

are you being required to do the "test 2" type? that being the dyno type. i hurried and got all my rigs done prior to oct 1 when it changed here in the bay area. it is suppose to fail about 30% of the cars that would have passed the old test.

[sammyg2]

They put it on the rollers and tested it at 15 and 25 mph, is that the test 2 type?

Oh, the good news is that my gas cap passed the gas cap test

[Bob's Flat-Six]

My 80 SC was tested back in 6/03 and passed on the rollers, in fact everytime I've had it tested (3 times) it's been on rollers and passed everytime.
The CO measured .42 at 15 mph and .15 at 25mph. It's pretty much stock and the readings on all the test have been in the same range.
I'm not sure what is causing your's to fail, Sammy
But I'm curious if a Cat going bad could be the problem?? but thats just a guess

[HarryD]

Let's talk a bit of chemistry here. T

his is the chart from Bosch Fuel Injection & Engine Management (thanks Steve W). The solid line is with a cat and the dotted line is without one.



Anyway, you can see from this chart that by making the mixture more lean (less excess air), you drive the CO down, but the NOx and HCs go up.

A question is how do your HC's and NOs look. If they are high, it is possible your catalyst is dead. If so, you may notice that the CO is the one most greatly controlled by the catalyst and this could be why you are not passing.

Hope this helps a bit.

[tobluforu]

Bad cat and o2 sensors will cause all sorts of havic when testing. Run low octane gas; tune car up, retard timing a few degrees. If cat is old-replace. Same goes w\o2

[Doug Zielke]

Sam,
I just smogged the 'Bomber a couple of weeks ago. Our test stations here are modeled closely on CA specs, so they are pretty tough.

First off, I do *not* run a cat. My car manages to get through on a 'loophole' in the rules without one. All I did was lean the mixture to around 0.5% CO (using my Gunson), connect the O2 sensor, set the timing to around 0 BTDC, and roll to the test. Oh yeah....I filled the tank at a station that dispenses gas cut with 10% Ethanol.
The car passed with ample margin on *all* the exhaust gases. Still, no cat.

What puzzles me about your test, is how you wrench could set it at 0.18%, and yet it fails the test with a much higher reading.
What is happening there??
If your motor has a functioning cat and 02, you should pass with ease.

[makaio]

Not to higjack your thread Sammy, but is it possible for a California resident say in Orange County, to have a smog test done in Shasta County? Or does it have to be the County in which you reside in?

[sammyg2]

The owner of the Porsche shop set the CO with the car idling, but the test was done on rollers at 15 and 25 mph.

That's the part that bothers me the most, the car was lean at 900 rpm but went rich at 2500 rpm during the test.

I do believe the O2 sensor was suspect, but the only other explaination I can come up with it either a vacuum leak that has more effect at idle than at 2500 rpm, or the air flow metering isn't linear to the fuel flow.
Still sctartching my head on that one. My CIS books are at work, I bet you can guess how much actual work I'm going to get done tomorrow morning

I really need access to a gas tester so I can diagnose and tune it. I can't afford to keep going to a shop to have fine tuning done when it doesn't accomplish getting the car to pass.
I also can't rely on tuning it by ear (obviously). I've gotten by for too many years doing it that way but this time I need to be more precise.

Matt, sorry I can't answer you question, I have no idea. Have you checked the Ca. DMV website for a FAQ or something?

[makaio]

Yes, I have looked at it, but it was a couple years ago. I was just thinking that if you guys in the "rolling test" counties could test outside the county your car was registered in, say like the county I live in that doesn't do rolling test, it would be easier.

[Joe Bob]

Chock the front wheels and put the car on jack stands.....rev her up in gear.....

[scottb]

Try taking it to a different test station next time.

[Early_S_Man]

Sam,

O2 sensors don't fail 'partially!' It is probably the cat ... how many miles on it ?

At this point, it sounds like you have already spent about what a Gunston would have cost you ...

Get one and do a test as MikeZ suggested at 2500 rpm in 1st gear with tail up on jack stands. It would also be a good idea to drive the car for at least 30 minutes at highway speeds just prior to going to the next test.

[emcon5]

Originally posted by makaio
Yes, I have looked at it, but it was a couple years ago. I was just thinking that if you guys in the "rolling test" counties could test outside the county your car was registered in, say like the county I live in that doesn't do rolling test, it would be easier.

Matt, I'm not positive, but from experience, I believe the CA DMV knows what test is required where the car lives, and if you tried to get a "enhanced area" car checked somewhere else, it would reject it.

Before I bought it, my SC was registered in Sacramento, which was aparently an "enhanced" area. When I tried to smog it for license renewal, the (networked to the DMV) smog machine spit out an alert that I had to go to a "test only" station, with no indication as to why.

At the time there were no test only stations in the Bay Area. I called the phone number the smog place gave me, and after being on hold and bounced around between 4 or 5 people, I was told that it was because it had been registered in an enhanced area. They made some change at their end which took the "test only" flag off and it passed with flying colors.

As of a couple weeks ago, the SF Bay area is enhanced, and we need to do the rollers now.

Tom

[emcon5]

Originally posted by Early_S_Man
Get one and do a test as MikeZ suggested at 2500 rpm in 1st gear with tail up on jack stands.

On a related note, do you have the option of what gear you are in for the test? Couldn't you do it in 4th gear, which would be damn near idle? How does that work?

Tom
(who needs a smog check early next year)

[Kurt B]

I passed (failed for NOX) by putting in an O2 sensor --had the guy dig in boxes for a 3 wire one that I could wire in rather than spend $$ on the original type which is 4 times more...
Richened it up to 3% and put lots of octane booster (to keep NOX down).
In your case, you need to lean it out more and then put in octane booster, and make sure O2 sensor is working.

[dvkk]

Placing the rear on jackstands won't do anything for you. You could rev it to 2500 in neutral and do the same as driving it in the air. The test in the smog station applies a significant load on the engine, changing the way the FI system reacts compared to reving it to 2500 in neutral.
Your running the car for years with the O2 sensor disconnected will have certainly killed the CAT. I don't understand why so many on this board disconnect the O2 sensor.
When they have the car on the rollers what gear are they using for the 15 and 25? If they shift into 3rd for the 25mph test the engine will be lugging, causing the NOx to climb. Ask if they are allowed to leave it in 2nd. If they have an rpm limit, you can temporarily install taller tires to drop the r's to within their limit. Where I live, the 25mph test is dictated to be in 2nd, and on 2 occations I have caught the guy shifting into 3rd.

[Kurt B]

didn't see this;
"900 rpm but went rich at 2500 rpm during the test."

That sounds like an airflow meter problem. Two years ago, when I was a "gross polluter" I was OK at idle, then my CO went through the roof under load. Replaced the airflow meter, and it passed. Now I have other problems (misfiring cylinder or something), that's making it hard--but I did still pass.

[Doug Zielke]

There is *no* airflow meter on a CIS car.

Sam....I gather you are still running a cat?
If so, the idea of a bad (dead) O2 sensor killing the cat makes sense.