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High Altitude Study Report
Part 5

1984-1985 GM/Jeep LDGT 2.8L
Non-Feedback Varijet

Data Analysis

The data analysis of the GM 2.8L non-feedback carbureted system indicated the system would require modification to pass I/M 240 final standards while allowing a normal catalytic converter life expectancy. Of the 13,288 1984/85 vehicles in the data sample, 1,003 passed within final standards on their initial test. This indicated the need to modify 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, 2,048 models were identified as marginal. 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 42 owners contacted, one 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. Fifty-seven 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 one owner responded, but was 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:

One vehicle owner contacted DTEC as a result of the recruitment process. The vehicle owner had a difficult experience in 1995 while trying to get his GMC Jimmy to pass the I/M 240 emissions test. The vehicle required a tune up and carburetor overhaul with several adjustment attempts before passing at just within the CO standard. Driveability suffered after these adjustments requiring a final driveability adjustment after the vehicle passed the I/M 240 test. DTEC contacted several Master Technicians in the area regarding these vehicles. Each technician identified the most likely causes of failure as inoperative catalytic converters, low altitude carburetor calibration, inoperative air injection systems, and saturated EVAP canisters. All of the technicians interviewed had attended EDGE training. Average repair costs were $341.00. Equipment used included a gas analyzer, labscope, and DVOM. The technicians viewed understanding of the specific operating strategies and the need for a recalibration strategy as the most important skills 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:

The vehicle owner responding to the mailing indicated he only needed a catalytic converter to get his vehicle to pass the I/M 240 test. The vehicle passed with a CO reading above 65 grams per mile (gpm). This indicates the need for further calibration to ensure normal life expectancy of the catalytic converter. The technician had attended various emissions classes including Colorado State University and EDGE. The technician used a gas analyzer and basic test equipment while using an EDGE-type diagnostic strategy.

Results:

After interviewing the technicians and customers, it was determined the system would require recalibration to pass the I/M 240 emissions test. 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. A young man who had suffered through several repair attempts owned candidate vehicle #1. A Public Service Co. employee who responded to the study mailing owned candidate vehicle #2. Candidate vehicle #3 was owned by a high school student. 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 GM 2.8L candidates. All three vehicles required modification of the carburetor as outlined in the GM 2.8L course. Each vehicle also required replacement of the catalytic converter, as all three were completely hollow. The driveability of all three vehicles improved dramatically with a marked improvement in fuel mileage. The Federal Test Procedure (FTP) results verified the accuracy of the calibration with results at or near certification standards. The results indicate modifying the system 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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