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OAR Box 1830 

Prepped by Ollie Stewart 

Document Number: 

31) IV-B-27 

Docket Number: 

A-87-11 

Printed 11/13/2008 7:20:52 AM Sheet 31 of 232 
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I*0"*** 

|V-B-2r 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

JAN 2 A 199/1 j | 

MEMORANDUM 

kNN ARBOR. MICHIGAN 48105 

JAN B 5 1S9^ OFFICE OF 

AIR AND RADIATION 

SUBJECT: 

FROM: 

THRU: 

TO: 

Estimate of Reduction in Evaporative System Purge 

Failures Resulting from Recent EPA Actions 

Dan Barba, Mechanical Engineer \)<Lv\ iSeJ-Jv^ 

Engine and Vehicle Regulations Branch 

Don Kopinski, Project Manager 

Engine and Vehicle Regulations Branch 

Glenn Passavant, Branch Chief 

Special Regulatory Projects Branch 

This memorandum estimates the reduction in evaporative system 

purge failures resulting from Inspection and Maintenance (I/M) 

programs [57 FR 52950, November 5, 1992] and onboard diagnostic 

(OBD) systems [58 FR 9264, February.19, 1993]. Percent reductions 

in failure rate are estimated over the full useful life of a 

vehicle, as defined under the Clean Air Act [58 FR 29409, May 20 

1993]. 

The attached figure shows how evaporative system failure rates 

are modeled in MOBILE51. The data shows that the purge failure 

rate is fairly constant (3.5 percent) over the useful life of the 

vehicle (50,000 miles for current vehicles). It is reasonable to 

expect that the failure rate will be maintained over 100,000 miles 

as a result of full useful life requirements. Thus, in this 

analysis, the purge-failure rate is projected to be 3.5 percent 

over the full useful life of the vehicle (10 years/100,000 miles) . 

The enhanced I/M program requires vehicles to undergo a 

functional test of the purge system. If a vehicle fails the test, 

the purge system must be repaired. Although basic I/M does not 

require a functional test, the final I/M rule requires states to 

revise their state implementation plans (SIPs) to incorporate 

inspection of the OBD system, which includes a purge system check 

similar to the enhanced I/M purge test. Thus, it is expected that 

failed purge systems will be identified and repaired in both basic 

and enhanced I/M areas. 

1,TDraft MOBILE5 Hot Soak and Diurnal Emissions," handout from 

EPA MOBILE5 Workshop, July 8, 1992 (Docket A-89-18, item IV-B-8). 
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The regulatory support document for I/M assumed that all purge 

failures caught by I/M testing would be repaired. However, because 

inspections are not normally required on brand new vehicles, purge 

failures will not be identified until after the vehicle is at least 

one year old, assuming an annual inspection. In fact, because I/M 

inspections are tied to annual vehicle registration requirements in 

many states, a new vehicle may not be required to receive an 

inspection until it is almost two years old. 

The regulatory support document for I/M assumed no vehicles 

will receive an inspection during the first year of vehicle 

operation and 25 percent of the vehicles will receive an inspection 

during the second year of operation.2 After the second year, all 

vehicles are inspected and the repair rate is 100 percent. The 

average inspection rate, and thus the average reduction in purge 

failures, over the 10 year full useful life of a vehicle is 

approximately 80 percent ([1*0.0 + 1*0.25 + 8*1.0]/10). 

In areas without I/M, OBD systems alone are expected to result 

in a substantial reduction in purge failure rate. In a survey 

conducted for EPA by Westat, Inc., 60 percent of vehicle owners 

sought repair after a dashboard light indicated an engine 

malfunction.3 Thus, it can be estimated that 60 percent of purge 

failures caught by the OBD system will be repaired in areas without 

I/M. 

Attachment 

2 11 I/M Cost, Benefits, and Impacts," EPA, November 1992, 

3"Survey of Vehicle Owners in the On-board Diagnostics 

Program," prepared for EPA by Westat, Inc., 18 July 1990 (docket A90-35, item II-A-6) 
M0BILE5 Pressure and Purge Failure Rates 

mi 

Failure 

Rate 

(%) 

70 

60 

50 

40 

30 

20 

10 

+ + + + + + 

~ Pressure 

"" Purge 

— Press or Purge 

20 40 60 80 100 120 140 

Mileage (x 1000) 

160 180 200 

-o