Ok, my car failed the enhanced smog test in California. High NOx at 15mph (and near failing at 25mph)

California purch. 1986 740GLE Wagon, B230F Engine (non-turbo), 245K Miles (new catalytic converter 5 years ago)

1. clogged /partially clogged EGR Valve, EGR pump, EGR pump hoses

2. a vacuum /vacuum hose leak

3. injector seal leaks

4. lean fuel condition (from bad O2 sensor)

5. clogged flame trap? (NOT SURE)

6. over advanced timing (or timing is off)

7. bad catalytic converter

15Mph (1769 RPM)

NOX (ppm) 1276 – 1125 max (399 avg) - FAILED barely

HC (ppm) 58 – 133 max (41 avg) – pass

CO (%) 0.39 – 0.82 max (0.13 avg) – pass

%CO2 – 14.7 – pass

%O2 – 0.3 – pass

25Mph (1810 RPM)

NOx (ppm) 935 – 955 max (332 avg) - passed barely

HC (ppm) 36 – 108 max (29 avg) – pass

CO (%) 0.32 – 0.62 max (0.11 avg) – pass

%CO2 – 14.8 – pass

%O2 – 0.2 – pass

High NOx and low CO, HC mean you are running lean and/or hot.

New cat won't affect NOx.

My car also failed first try on NOx. Here is what I did to pass:

1. Replaced distributor cap and rotor - old ones were really corroded badly.

2. Replaced fuel filter (which seemed partially clogged) to ensure adequate gas supply.

3. Fixed IAC valve.

4. Adjusted base idle speed to correct value.

5. Replaced O2 sensor so mixture would richen up properly.

6. Checked timing.

7. Checked cooling system to make sure engine would run cool as possible.

Really just tune-up items. Car passed no problem on second go.

Reasons aside, I suspect that if you retard your timing by 3 degrees, and use premium fuel to reduce combustion temperatures, and precondition the car by driving for 45+ minutes without turning it off as you wait at the smog shop, you have a good chance of passing. New spark plugs never hurt your emissions either.

California checks timing as part of the emissions test. Assuming his car has vacuum advance on the ignition computer...he can temporarily plug the vacuum line going to the ignition computer with a screw/ball bearing/glue which will put the car into some pre-programmed ignition mode. Did this with my '87 245 and it worked beautifully. Not sure about the configuration on the '86 7xx series but my assumption is that it is the same or similar.

Bean
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'80 242GT 92k, '94 945T 123k

rotating the distributor should move the pickup and alter base timing.
CA allows 3 degrees retarded from stock setting before they fail you. I know cause I trained as a smog tech ; )

Damien,

Just in case you don't have the "notify by email" button clicked when posting... I responded to your original post, check back there for some explanations.

Good luck,
Bean
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'80 242GT 92k, '94 945T 123k