VVC AUTO 85.5 - Smog Technician - Level 1 - Baseline testing

Advanced Emission Diagnostic Training

Why baseline Before and after repairs

Baselining with a 5 gas analyzer Baselining with a scope, scan tool, or DVOM Correlation of baseline reading with Bar ‘97

test results


Diagnosing an emission failure is different from many auto repairs

Sometimes a vehicle will “run fine” but fail a smog test

It can be hard for a tech or customer to visualize a smog failure


A baseline test consists of: Monitoring all 5 gases at: Stabilized operating temperature Idle 3000 RPM (no load) ASM mode 1 ASM mode 2


Performing a baseline test before and after a repair will be an indication of how successful your repair was

Sometimes a repair of one gas will raise another gas out of limits

Remember you are going to compare the two sets of readings, so always perform a before and after baseline test exactly the same, or results will be inaccurate


Analyze the “after repair” baseline readings and the “before repair” baseline readings by comparing the two sets of readings.

Calculate the difference in percentages If the percentage of reduction is the same

or higher (cleaner) Your repair was probably successful Be sure to check the other gas readings


Equipment used to gather baseline readings DVOM

Hook up to 02 sensor Positive lead to 02 sensor return wire Negative lead to good ground

Scan tool Hook up and program


DVOM to fuel injector (if no data stream) Positive lead to fuel injector ground Negative lead to good ground Set on ms scale

Warm up vehicle Monitor the O2 ( voltage & frequency)

and the Injector (pulse width) simultaneously. O2 should fluctuate above and below .450

volts at least once every couple of seconds A rich exhaust must = a lean command


If 02 sensor reading is biased high or low you have a problem (may not be 02 sensor)

Baselining using the 02 sensor and M/C command will monitor CO only


A digital storage oscilloscope (DSO) will give more accurate information

If a small misfire is present more oxygen is in the exhaust stream

The 02 sensor wave form will have a higher frequency

Using this method only CO & HC problems can be identified


BAR ‘97 analyzer Road test -- put on analyzer Monitor and record all 5 gases during 4

conditions mentioned before Other test equipment utilized during this

baseline test may include timing light, DSO, Digital Pyrometer etc.


Special note: If all OEM emissions equipment is not hooked up and operating as designed, baseline test results will be inaccurate. (missing, modified or disconnected emission systems must be repaired first!)

Automotive

VVC AUTO 85.5 - Smog Technician - Level 1 - Baseline testing