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High Altitude Study Report
Part 8

1983-1987 Toyota Tercel
Computer Controlled Emissions

Data Analysis

The data analysis of the Toyota Tercel feedback carbureted system indicated the system could be repaired to pass I/M 240 final standards. Of the 3,513 1983/84 vehicles in the data sample, 22 passed within final standards on their initial test while 97 of the 1985/87 models passed within final standards on their initial test. This indicated the ability of this system to pass at or within final standards.

Filters were applied to identify the vehicles that failed their first test, had multiple repair attempts, and passed the I/M 240 emissions test but would not have passed final standards (see note at bottom of page for final standards info). With these filters applied, ten 1983/84 models were identified as marginal as were 21 1985/87 models. The vehicle owners were contacted via mail through the use of Colorado Department of Revenue (CDOR) records. These owners were offered free repairs to their vehicles if they would participate as study candidates. Of the 31 Tercel owners contacted, none responded.

The filters were re-applied to identify the vehicles that had failed the first test, were repaired, and passed the second test within final standards. One 1983/84 vehicle and eleven 1985/87 vehicles were identified. The owners of these vehicles were contacted via mail through the use of CDOR records. The owners were asked if we could contact the repair technician to determine what repairs were made and how the technician approached the repair. Only three owners responded, but were very helpful and cooperative.

Interviews

The interview process was carried out over the phone with responses listed in this section. Owners were interviewed about the experience and asked if we could contact the technician if applicable. In all cases the owner had repairs made by a technician.

Vehicles that failed the initial test, had multiple repairs, and passed but not within final standards:

Since no customers responded to the mailing, DTEC contacted several of the Toyota Master Technicians in the area. Each technician identified the most likely causes of failure as the oxygen sensor, vacuum hose routing or degradation, vacuum switch operation, EBCV contamination, and carburetor overhaul. All of the technicians interviewed had attended EDGE training but commented that Toyota did not offer specific diagnostic information for the feedback-carbureted systems. Average repair costs were $275.00. Equipment used included a gas analyzer, labscope, and DVOM. Understanding of the specific operating strategies was viewed by the technicians as the most important skill required to properly repair these vehicles to pass the I/M 240 test.

Vehicles that failed the initial test, were repaired, and passed within final standards:

Of the three vehicles identified as repaired properly, one required an oxygen sensor, one required a thermo-vacuum switching valve and the third required an oxygen sensor replacement and EBCV disassembly and cleaning. The repairs were performed by two independent garages and one dealership. The average time to repair the vehicles was less than one working day at an average cost of $268.00. The technicians all had attended various emissions classes including Colorado State University and EDGE. Each technician used a gas analyzer and a labscope or DVOM using an EDGE-type diagnostic strategy.

Results:

After interviewing the technicians and customers, it was determined the system could pass the I/M 240 if operating as designed. During the validation phase of the study, the EDGE diagnostic strategy would be applied to the study candidates.

Recruitment

All of the study candidates were referred by the State Technical Centers. Candidate vehicle #1 was owned by a young man employed at a rental car agency at Denver International Airport. Candidate vehicle #2 was a Chevrolet Nova that had been issued a waiver. This vehicle was allowed into the study with permission of the Colorado Department of Public Health & Environment (Air Pollution Control Division) since it uses the same basic fuel system and test results were typical of the identified sample. Candidate vehicle #3 was owned by a young man who performed the repairs himself. All were willing to participate and were very satisfied with the results of the study and the repairs made to their vehicles. Each vehicle was returned to the owner clean and full of gas.

Validation

See the related documentation for further information on the diagnosis, repair, and validation of the three Toyota candidates. Vehicle #1 required cleaning the EBCV, repairing a connector, and replacing several clogged vacuum lines. Vehicle #2 needed a TPS and an oxygen sensor. This was a recently-waived vehicle with a new catalytic converter. Vehicle #3 required a new oxygen sensor, repairing a broken vacuum line, and overhauling the carburetor. The results indicate repairing the system to operate as designed will result in a successful repair.

Documentation Notes

Accompanying vehicle documentation and the technician guide for this group of vehicles are available in the printed version of this report, available from the Colorado Air Pollution Control Division, 303-692-3126. We plan to add the tech guides to this website as PDF files in the near future.

"Final standards" refers to U.S. EPA recommended final emissions standards. These can be found at the EPA website at www.epa.gov/oms/epg/techguid.htm. Click on the "6/96 Draft Revised IM240 Technical Guidance" item, and go to page 3. Note high altitude standards. You will need Acrobat Reader to view this PDF document. It is free from the Adobe website.

More Info

  Part 1: High Altitude Project Profile
  Part 2: Project Methodology
  Part 3: 1982-86 Chevrolet LDGT 5.0/5.7L; Non-Feedback Quadrajet
  Part 4: 1983-85 Ford LDGT 4.9L; EEC-IV Feedback Carburetor
  Part 5: 1984-85 GM/Jeep LDGT 2.8L; Non-Feedback Varijet
  Part 6: 1984-85 Low Altitude Honda Accord; Carburetor Feedback System
  Part 7: 1985-89 Imports: Hyundai, Mitsubishi, Plymouth; Feedback Carburetor System
  Part 8: 1983-87 Toyota Tercel; Computer Controlled Emissions

Chris Chesney is the owner of Diagnostic Technician Education Consultants (DTEC), 5497 S. Danube Way, Aurora, CO 80015. He can be reached at 720-870-6761 or via email at chesneydtec@cs.com. Chris has trained hundreds of technicians in I/M 240 diagnosis and repair.

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