Failed CA TEST ONLY smog test

[FreddieWilliams]

Test-------RPM--CO2(%)--O2(%)--HC(PPM)--CO(%)--NO(PPM)
15 MPH---2214--13.77------1.64------53------0.03-----748---------PASS
25 MPH---2053--13.60------1.69------35------0.02-----1012--------FAIL

Max 15 MPH----------------------------------------------------772
Max 25 MPH----------------------------------------------------711


Checked the EGR valve function today and all seems well. Verified 17+ inches of vacuum going to the EGR solenoid. EGR filter is clean but removed it anyway. EGR valve holds vacuum good (i.e. no leaks in diaphragm). Verified EGR valve activity/movement when EGR % duty cycle was commanded via the ECM.


What other things could contribute to my high NOx reading at 25MPH????

Your help is greatly appreciated.

Signed, out of ideas.

 

[Aztlanahauc]

cooling system......does your car run hot...NOX is caused by high temps in the combusion chamber..

timing.....

and also the cat helps in cleaning up NOX...

 

[gofstbuick]

And gear selection. How come the test was at 2200rpm? Should be around 1500-1600rpm. Did the tech test it in 2nd gear? It's suppose to be tested in drive (not OD either)

 

[Taffy]

The 25 MPH test has to be above 2000 RPM. No exceptions.

 

[FreddieWilliams]

Aztlanahauc,

My cooling system is fine and does not run hot.

Timing maybe a little high (4-6 deg) due to the BMS balancer.

The cat is the original stock 1987 cat conv and could be on its way out.

Thanks for all the leads.

 

[gofstbuick]

Originally posted by Taffy
The 25 MPH test has to be above 2000 RPM. No exceptions.

The calculation for determine RPM for a given MPH, gear ratio and tire diameter is as follows:
RPM=MPH x gear ratio x 336/tire diameter

If we assume a 26.1 tire diameter (typical 235/60/15 or 215/65/15), that yields approximately 1100 rpm. But this does not account for the fact that the torque convertor is fully locked or load. So around 1500 rpm should be correct for the 25mph portion of the CA ASM smog test. If the RPM exceeds 2000 during the 25mph test, one can only assume that the test was performed in the wrong gear (probably 2nd gear). The smog check manual clearly states that an automatic transmission vehicle is required to be tested in drive (not overdrive or second gear), and overdrive shall be selected if the RPM exceeds (during the test) 2500 for an engine that is larger than 3.0L.
Second gear is only used for manual transmissions vehicles and specific RPM limits allow changing gears up or down on the test.

 

[Mac in SD]

Freddie, maybe I missed it, but did you check to see that the EGR passage is clear? Over the years, they can clog up with carbon. I ran into that on an 87 Toyota back in '98. Just a suggestion. Or throw some alcohol in your gas.

 

[FreddieWilliams]

Mac,

I already verified that the EGR passage was free and clear. Manually lifting the EGR diaphragm causes a noticeable stubble in idle. Also the motor has only been in the car for 4 months and has maybe a few thousand miles.
I also teed in a vacuum gauge between the EGR valve and Solenoid to verify that the ECM commanded EGR duty cycle % was actually activating the EGR valve. This too checked OK.

Next step is to rerun the test with a stock O2 to help richen the mixture a bit and add a new cat converter.

Thanks for the suggestion.

 

[FreddieWilliams]

Got the car to pass smog last weekend.

Thanks to Neal Steward lending me his brand new 3" cat. The Nox cleaned right up.

I did also change out a brand new Casper's heated O2 with a stock single wire thinking it might be too lean. With these two changes (stock O2 & new Cat) the test only smog check is behind me.


Thanks again for all your suggestions.