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Project at a Glance

Project Status: complete

Report Published June 1973:

Title: Evaluation of the effectiveness of automobile engine adjustments to reduce exhaust emissions and an evaluation of the training required to develop personnel competent to make the adjustments

Principal Investigator / Author(s): Gockel, J. L.

Contractor: Clean Air Research Company

Contract Number: ARB-654

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels


A study was conducted to explore two approaches for the control of exhaust emissions from used vehicles. The first approach involved the upgrading of Class A stations with exhaust analyzers and the training of Class A mechanics to perform low-emission tune-ups. Ten Class A mechanics, representative of Class A mechanics as a whole, attended a 40-hour training course. They learned how exhaust emissions relate to the condition of the engine. With this knowledge, they were "programmed" to:

1. Quickly diagnose engine defects that cause excessive emissions.
2. Repair these defects.
3.Maintain certain engine components to prevent malfunctions known to cause emission increases.
4.Perform low-emission adjustments.

The above steps reduced engines to their practical minimum pollution capability (MPC) and are referred to as an MPC tune-up. MPC tune-ups were completed on 300 vehicles representative of the 1957-1970 California vehicle population. Hydrocarbon (HC) and carbon monoxide (CO) emissions were reduced by 36.7% and 35.2% respectively. Exhaust oxides of nitrogen (NO,) increased 5.6%. The average cost was $27.40. Fuel consumption was reduced by 5.0%. Interviews with the vehicle owners revealed that 54% of the vehicles performed better, 15% worse, and 31% with no change.

After an average mileage of 5253 miles and six months of service, the vehicles were retested. Degradation in emission control was small. HC and CO reductions were still 29.5% and 30%, respectively. NOx increase was 3.7%.

The second approach involving the vacuum spark advance disconnection (VSAD) on engines for NO, control was studied to determine the vehicle owner's acceptance and possible side effects. The scope of the study was limited to driveability changes and side effects noticed by the vehicle owners during the first month of service. VSAD was provided on 100 vehicles previously given MPC tune-ups and 100 like vehicles with no other work performed on the engine. Fifty (50) vehicles representative of the 100 vehicle groups were equipped with "dummy" VSAD kits, therefore, establishing and compensating for owner bias in the
data analysis.

The results showed that vehicle owners could not distinguish between the "real" and "dummy" VSAD kits when no other work was done to their engines. VSAD combined with the lean tuning in the MPC tune-up produced a change in driveability unacceptable to one out of five vehicle owners, An investigation of coolant overheating complaints showed that VSAD had a slight effect. Faulty cooling systems were the major cause of engine overheating.


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

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