Another CA smog issue

Avery · 10-28-2005, 05:56 PM

My 1983 911 failed the smog test last week. I'm a "gross polluter". The motor was checked out by Jerry Woods and declared in good shape before I bought it and installed it. Here's my test results:

@15 mph
%02 - 0
HC - 212 ppm (141 max)
CO% - 2.41 (.99 max)
NO - 248 (1148 max)

@25mph
%O2 - 0
HC - 205 ppm (113 max)
CO% - 2.31 (.79 max)
NO - 183 (978 max)

After the tests, I checked the emissions with my Gunson. I got CO% levels at around .02!!!! Of course, my car was not under load when I did my tests but how could our results be that far aparts? Also, my timing was found to be 6% BTDC. I'll reset the timing to TDC per spec. I plan to install new plugs and sensor in the hopes of getting the car to pass. I can adjust the fuel dist mixture but since I'm getting low CO readings on my GUNSON, I'm wondering how I can adjust the emission correctly to pass the test on the next go around? Should I be sticking the GUNSON probe upstream of the cat? Any advice is most welcome.

cab83_750 · 10-28-2005, 06:34 PM

At .02, do you still have your cat? In other words, I assume you inserted the probe at the tail pipe with an operating catalytic converter.
If so, remove the oxygen sensor and insert the probe inside (I am no expert but you may be able to do it!).

CO reading should be without a cat. I have a Gunson and it is very sensitive.

I am not shocked about your reading. I may have misread my old reading but I swear it was -1.1. Go figure>

Good luck!

2.7RACER · 10-28-2005, 06:35 PM

Do a search on the "Ultimate California Emissions Thread"
Lots of good info.
Looks like you need to lean out the mixture, but I'm not an expert.

klatinn · 10-28-2005, 08:28 PM

Hi,

Yes you are running rich. Low NOx and High CO and HC indicate that. When running with an O2 sensor connected (closed loop) this can have 2 reasons:

1. Exhaust air leaks make the O2 sensor read lean. Therefore ECU richens up. But your O2 reading is zero, therefore you have no leaks.

2. O2 sensor old or damaged. It can't get it up anymore (the voltage). This indicates lean to the ECU and it richens up. Verify that during idle/part throttle the O2 voltage is around 0.45V.

FYI:
I just passed my daughters CIS VW Golf through CA smog (170,000 miles).

15mph
HC = 11 (135 max)
CO = 0.08 (0.99 max)
NO = 452 (1150 max)

25mph values were about the same
All values way below average for all passing cars.

I adjusted the CIS to exactly Lambda 1.00 with an LM-1. Cat on the car is still the original one.

Regards,
Klaus

Lorenfb · 10-28-2005, 11:17 PM

Other reasons:

1. Gunson reading is incorrect.
2. Lambda unit not functioning properly or not connected.
3. Mixture is too rich beyond Lambda control.
4. Bad fuel distributor causing rich mixture under load.

Avery · 10-29-2005, 05:24 AM

Thanks Loren:

The car runs great all around. No problem cold starting, pulls strong, no smoke... so I really want to think the fuel distributor and Lambda are at least working. You can hear the Frequency Valve buzzing so the computer is at least connected. I'll change the plugs and O2 sensor, and retime and see what happens. I think (hoping) the mixture is just too rich to allow the Lambda to bring the A/F ratio down.