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EXPERTEC TSB (92-7A-102)

Publication date: 1992-06-22
Reference number: 92-7A-102

EXPERTEC TSB

EXPERTEC TSB

TECHNICAL SERVICE BULLETIN

Reference Number(s): 92-7A-102, Date of Issue:  06/22/92

LACK OF POWER/TRANS HOT MODE - INST MEMCAL/CHECK THERMAC DOOR

Model(s): 1991-92 Trucks with 4.3, 5.7, 7.4L Engines

Bulletin No.: GMC 92-7A-102

Date: 06/22/1992

CONDITION

Some owners of 1991-92 trucks with 4.3, 5.7, 7.4L engines and 4-speed automatic transmission (4L80E) may comment on the following conditions:

4.3L (RPO LB4 with MT1 transmission)

5.7L (RPO L05 with MT1 transmission)

  1. Transmission converter clutch (TCC) is locking too early in 2nd, 3rd, and 4th gears and may be perceived as lack of power at highway speeds.

    7.4L (RPO L19 with MT1 transmission)

  2. Tach needle flutters on decelerations.
  3. Catalytic converter odor.

CAUSE

4.3/5.7L with MT1 transmission

  1. Transmission hot mode, which causes TCC lock-up in 2nd, 3rd, and 4th gears, entry temperature is too low.
  2. Thermac door in air cleaner may not be fully opening. This may cause the engine to operate on warm air, lowering power.
  3. Engine fuel calibration is not optimal.
  4. At idle, the engine goes into an open loop condition which does not provide precise fuel control, possibly leading to catalytic converter odor.

7.4L with MT1 transmission

SERVICE PROCEDURE

4.3/5.7L with MT1 transmission

  1. Transmission hot mode entry temperature raised from 252 degrees Fahrenheit to 270 degrees Fahrenheit. Install MEMCAL per attached charts.
  2. Check Thermac door in air cleaner for correct operation. Door must open and close freely with no sticking or binding.

    7.4L with MT1 transmission

    Install MEMCAL per attached charts for corrections 1-3.

  3. Engine decel fuel calibration revised.
  4. Engine idle revised from open loop to closed loop.

SERVICE PARTS INFORMATION

In case of limited inventory, parts will be placed on 400 control to waive VIP surcharges. Only verifiable emergency VIP orders will be accepted. GMSPO will make every effort to obtain parts. However, the part will be shipped premium transportation at dealer's expense and all other order types will be placed on backorder until the 400 control is removed.

WARRANTY INFORMATION

Labor Operation: T0500 - MEMCAL

Labor Time: 0.6 Hr. on C/K, RN, and P models

0.5 Hr. on G models

Fig 1: 1991-4.3L / RPO LB4
GB0039440
Fig 2: 1992-4.3L / RPO LB4
GB0039441
Fig 3: 1991-7.4L / RPO L19
GB0039442
Fig 4: 1991-7.4L / RPO L19
GB0039443
Fig 5: 1992-7.4L / RPO L19
GB0039444
Fig 6: 1991-92-5.7L / RPO L05
GB0039445
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