Emissions testing and diagnosis

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From the V6SHO list, 20 July 2007:

NOx is usually caused by excessive heat. Suspect the EGR system if present, thermostat, base timing (may be defaulting to 10 degrees BTDC, especially if there's a code 213 or 219). Can be reduced by running the test with the heater on and the shorting plug near the Self Test connector removed per Gary's recommendation (doesn't throw a CE light). [Ed. Note: See Gary information below.] I tried removing the plug once when I failed on Nox; this reduced output by a factor of ten.

HC is caused by a misfire/ raw gas. Suspect plugs and wires, leaking injector.

Codes may be present even though the CE light has not come on.

For the record, CO is caused by running rich: suspect O2 sensors, fuel system.

Nick Chrimes Owner, BaySHO Performance 1680 Almaden Expressway, Suite G San Jose, CA 95125 W (408) 295-4778


SPOUT = SPark OUTput; it's the signal that EEC sends to the ignition module to control ignition event timing and dwell. If SPOUT is disconnected from the DIS module, ignition timing reverts to base timing of 10º BTDC, which is determined by the crank sensor signal to DIS. The engine will run with fixed 10º timing, and NOX emissions should be reduced, and the engine will feel awfully flat. The SPOUT shorting bar is near the CID sensor. The other plug some have referred to is the ignition timing shorting bar. This is a hold-over from EEC's early days as a sort of Hail Mary to pull back everything in the timing tables by 2 or 3º. The idea being that if you got a load of crap gas, you could pull the timing jumper and back off the timing for awhile. On the SHO, the timing shorting bar is located in the harness by the driver's side radiator end tank. Gary Morrell Colorado Springs, CO