Emissions - Driveablity, Restricted Exhaust/Plugged Cat

Bulletin No. 85-35
File In Group 6E
Number 12
Date Dec. '84
SUBJECT: POOR PERFORMANCE AND/OR REDUCTION OF POWER

MODELS AFFECTED: 1982-1983 CADILLAC DFI HT4100 VEHICLES EQUIPPED WITH FEDERAL EMISSION SYSTEMS 1982-1984 CADILLAC DFI HT4100 VEHICLES EQUIPPED WITH CALIFORNIA EMISSION SYSTEMS

A condition of poor performance and/or reduction of power, possibly accompanied by delayed shift points, may be caused by a restricted exhaust system or plugged catalytic converter.

The following procedure can be used to detect an exhaust restriction and/or a plugged catalytic converter:

IMPORTANT: This procedure applies only to HT4100 engine vehicles equipped with beaded type catalytic converters. Using this procedure on other vehicles may result in an incorrect diagnosis.

1. Remove oxygen sensor and install a back-pressure tap #J35314 or equivalent into the manifold in place of the sensor. Connect a suitable 0-15 PSI pressure gage (J-29658 or equivalent).

2. Start the engine, enter diagnostics and observe engine data parameter .0.4 (coolant temperature). Allow engine to warm-up until engine coolant temperature reaches 85~C. Disable the A/C compressor by pushing the "outside temperature" button.

3. Display engine data parameter .1.1 (engine RPM). Block the drive wheels, firmly apply the brakes, place the vehicle in drive, load the engine against the brakes to obtain a steady 1600 RPM.

NOTICE: Total time during which engine is loaded against brake must not exceed 20 seconds.

CAUTION: Brakes must be applied at all times.

4. Holding a steady 1600 RPM, record the exhaust back pressure. Allow the throttle to close and idle to stabilize, place vehicle in park, and turn ignition key off.

5. If the pressure recorded in step #4 is 2.5 PSI (17.2 kPa) or greater, check for restricted exhaust and/or catalytic converter. Refer to step #7 below.

In the case of an advanced exhaust restriction, it is possible that a steady 1600 RPM is unobtainable. This is characterized by RPM and back pressure surging in unison, while holding a steady throttle position. Refer to Cadillac Service Information Manual to continue diagnosis of conditions not caused by an exhaust restriction.

If the pressure recorded in step #4 is less than 2.5 PSI (17.2 kPa), the condition is not caused by a restricted exhaust.

6. Remove pressure gage and back-pressure tap, apply high temperature anti-seize compound to the threads of the oxygen sensor (P/N 5613695 or equivalent), and reinstall the sensor.
7. If step #5 of this procedure indicates a restricted exhaust, the following are possible locations of the restriction:

^ EFE valve (if so equipped) not opening.

^ Restricted muffler.

^ Plugged catalytic converter.

^ Collapsed inner or outer exhaust pipe.

In order to isolate and correct the restriction, proceed as follows:

1. Inspect the EFE valve and verify that the valve is opening. If not, correct as necessary and retest.

2. Inspect the exhaust pipes for dented, kinked, or collapsed sections; replace as needed.

3. Remove the intermediate pipe to catalytic converter flange bolts and relocate the muffler and pipe assembly to one side. Test drive vehicle and determine if owner complaint has been eliminated; if so, replace the muffler. If the condition still exists, proceed to step 4.

4. Remove the catalytic converter and again test drive the vehicle. If the driveability condition has been eliminated, replace the catalytic converter.

5. If the previous tests fail to resolve the condition, replace the restricted section of exhaust pipe between the exhaust manifold and the catalytic converter.

If the catalytic converter is found to be restricted, this failure may be due to one of the following. To prevent the possibility of repeated failures, these possibilities should be thoroughly investigated.

1. Rich operation due to fuel system control problems or misfiring spark plugs.

2. Improper operation of the Air Injection Reaction (AIR) System.

3. Oil or coolant consumption due to broken or aligned piston rings, leaking intake manifold gasket or valve guide seals, or other mechanical causes.

4. Use of leaded fuel.