Calling all CA Smog experts

[e30pq]

I just failed smog and I need to figure out if my O2 sensor had anything to do with it.

I am running the M20 O2 sensor with an S50 motor and S50 cat.

The BAR referee thought it might have something to do with my O2 sensor.

Here are the results:

15 mph HC (PPM) max 85, measured 214 fail
15 mph CO (%) max .50, measured .72 fail
15 mph NO (PPM) max 695, measured 1776 fail

25 mph HC (PPM) max 50, measured 50 pass
25 mph CO (%) max .47, measured .10 pass
25 mph NO (PPM) max 717, measured 40 pass

Any suggestions?

[etxxz]

O2 sensors show different part numbers.....based on whats said, i think you answered your own question.

[MR 325]

The M20 and M50 sensors are not the same part. I can't guarantee they don't interchange but I doubt it. Have somebody hook your car up to a scanner and see if it's got any codes.

[hugh jass]

hmmm, you might want to check on an e36 forum and see what would cause you to fail at 15 but pass at 25. there will be more people there who have had to smog e36s.
did the ref let the cat get nice and hot?

[surebimmer]

I used the 02 sensor from my 89 325i it has the same plug connector and the wires are the same. But how old is your 02 sensor?

When was the last time you put plugs in this car? How many miles on the motor? Any mods to the motor?

[e30pq]

The car has about 2500 miles since the swap. I put new plugs in the car at that time.

The O2 sensor is about 7 years old. The car had a bad injector when I installed the motor. It had a miss for about a week before I figured it out. I could have damaged the O2 sensor during that time.

The motor has about 100k on it.

It has 24lb injectors, 3.5 540 HFM and Turner Conforti chip which accounts for the mods.

My M20 had 19lb injectors, M30 AFM and adjustable fuel pressure regulator and it passed smog without any problems. The AFPR should have failed the visual but I told him the stock one died and I put the AFPR instead.

[dvmotorsports]

cam kit? i have seen heavy cams fail smog at low rpm.

[e30pq]

cam kit? i have seen heavy cams fail smog at low rpm.

Stock cams

I ordered a new O2 sensor. I wish there was a way to check the car prior to going back to the ref.

[surebimmer]

Oh wow a 7 year old o2 sensor ya try that first.

[dvmotorsports]

Stock cams

I ordered a new O2 sensor. I wish there was a way to check the car prior to going back to the ref.

you can if you have a post cat O2 sensor. do you?

[e30pq]

I've got an a 95 OBDI cat so my O2 sensor is before the cat.

How would you be able to check the numbers with a post cat O2?

[dvmotorsports]

I've got an a 95 OBDI cat so my O2 sensor is before the cat.

How would you be able to check the numbers with a post cat O2?

you don't check the numbers, you check the voltage pattern with a scope and see the modulation. if it is modulating (see image below, middle picture) pre cat and flat line post cat, then the cat works. or vice versa (i can't quite remember). but if the signal is the same on both sides of the cat, it is failing.

look at this pic http://img.zdnet.com/techDirectory/_ASK.GIF
there are three diagrams. the pattern on a scope should resemble the middle picture.

[e30pq]

you don't check the numbers, you check the voltage pattern with a scope and see the modulation. if it is modulating (see image below, middle picture) pre cat and flat line post cat, then the cat works. or vice versa (i can't quite remember). but if the signal is the same on both sides of the cat, it is failing.

look at this pic http://img.zdnet.com/techDirectory/_ASK.GIF
there are three diagrams. the pattern on a scope should resemble the middle picture.

Thanks for the explanation.