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High Altitude Study Report
Part 6

1984-1985 Low Altitude Honda Accord
Carburetor Feedback System

Data Analysis

The data analysis of the low altitude-certified Honda Accord indicated the initial presumptions about the need to modify this system were false. Of the 3,355 1984 vehicle tests in the data sample, 1,042 passed within final standards while 393 of the 1,016 carbureted 1985 vehicles passed at or within final standards. Of the 9,576 total vehicles, 4,371 were carbureted with the balance being fuel-injected 1985 models. With 31 percent of 1984 and 39 percent of 1985 vehicles passing at or within final standards, every effort was made to determine if these vehicles could be repaired to pass without high altitude modification.

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, 38 1984 models were identified as were 74 1985 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 112 Accord owners contacted, four responded to the offer.

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 with 19 1984 models and 38 1985 models. These vehicle owners were contacted via mail through 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 four owners responded, but they 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 the repairs made by a technician.

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

Of the four responses, three had new catalytic converters installed, three had been "tuned up" and two had new carburetors installed. Each technician used old diagnostic strategies to identify the problems. The old style approach included the heavy reliance on the four-gas analyzer as the diagnostic and verification tool. All four technicians believed the readings from their gas analyzer would correlate to the I/M 240. The number of repair attempts averaged three with an average repair time of three days. Two technicians had attended dealer level training in the past 10 years, while all four admitted they had not attended any emissions-based training in the past 3 years. None of the technicians had attended any vehicle-specific training for Honda carbureted systems.

Three of the vehicles were finally repaired to pass with the installation of a new catalytic converter. One vehicle finally passed with the installation of a new carburetor. None of the "tune ups" worked and one of the new carburetors failed. Two of the vehicles had driveability problems after repairs. Repair costs ranged from $365.00 to $687.00.

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

Of the four vehicles identified as repaired properly, two were modified by enlarging the main air bleed to emulate the altitude compensator, one had a new high altitude carburetor and high altitude compensator installed, and one had a used high altitude carburetor and high altitude compensator installed. All the technicians had a basic understanding of the Honda CFS system. All determined the system was working as designed and modified to overcome the lack of fuel control. All performed only one repair, as these vehicles were not their first attempt at repairing low Altitude Honda Accords. All four used a gas analyzer to baseline the vehicle. Three used a labscope to view the oxygen sensor during road tests and verify fuel control. Two oxygen sensors were replaced initially while the modifications were needed to achieve fuel control during loaded conditions. All four technicians had attended various emissions training in the last 3 years. Four technicians had attended Colorado State University I/M 240 courses and three had attended EDGE training. All repairs were completed in one day with costs ranging from $140.00 to $1,500.00, with the expensive repairs consisting mostly of parts to install a high altitude compensator.

Results:

After interviewing the technicians and customers it was decided that more information was needed. A representative of American Honda contacted DTEC with concerns that vehicle modifications using the air bleed enlargement method were not acceptable. The concern was the possibility of the owner moving to a low altitude area causing a very lean condition and the difficulty in returning the jet to stock size. Interviews with many other technicians, including factory-trained technicians, made it very apparent that most technicians did not have a complete understanding of the operation of this system. Further review of the data identified a large number of vehicles that could pass the test without the use of modifications or high altitude compensators. American Honda was confident their system could pass any I/M 240 test if operating as designed. 

DTEC, therefore, gained access to a candidate prior to the start of validation testing to determine what diagnostic and repair strategy was required. The vehicle was a 1985 low altitude-certified Accord with 94,280 miles. The vehicle had several failed attempts with CO output of 74 grams per mile (gpm), HC output of 1.8 gpm and NOx output of 0.2 gpm. The vehicle had several repair attempts made with a tune up and carburetor adjustment being made unsuccessfully. The owner was complaining about marginal clutch slippage. DTEC replaced the clutch assembly and retested the vehicle with passing CO output of 23 gpm, HC output of 0.7 gpm and NOx output of 0.3 gpm. Fuel control was observed to be marginal during the preconditioning trip to the I/M 240 test lane.

The vehicle was returned to the repair facility and the EDGE chart was applied to determine the cause of marginal control. The oxygen sensor was found to be lazy and was replaced. During a road test the fuel control was viewed as normal and the vehicle was returned to the lane for testing. Results were CO output of 15 gpm, HC output of 0.4 gpm, and NOx output of 0.4 gpm. The vehicle was then returned to the repair facility and all components of the fuel control system were interrogated to determine the proper operating parameters of a low altitude-certified system. These results are included in the curriculum (see documentation note below) developed during this study. It was concluded that the proper application of EDGE strategies and a thorough understanding of the Honda CFS system would result in the proper repair of the low altitude-certified Accord without modification.

Recruitment

All of the study candidates were acquired through the State Technical Centers or the Air Care Colorado Technical Assistance Program. A University of Denver college student owns the first candidate vehicle. He had experienced much frustration at not being able to successfully get his vehicle to pass the test. The second candidate vehicle is owned by a woman from Boulder. She had experienced difficulty in getting the vehicle repaired properly. The third candidate vehicle is owned by a University of Colorado medical student who had unacceptable results with a Honda dealer. All were very willing to offer their vehicles in exchange for free repairs and a passing emissions certificate. All vehicle owners were very satisfied with the results of the study and the repairs made to their vehicles. Each vehicle was returned to the owner with a full tank of gas and a basic detail.

Validation

See the included documentation for further information on the diagnosis, repair and validation of the three Honda candidates. The EDGE strategy was applied to all three candidates with success. Candidate #1 required repair of vacuum lines and grounds damaged during a clutch repair. Candidate #2 required the replacement of the oxygen sensor while candidate #3 required the repair of vacuum lines, replacement of a vacuum switch, the adjustment of the float levels, and a new catalytic converter. The cost of repairs for each candidate was under the waiver limit of $450.00. The results indicate returning 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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