For 1990-2009 cars

# ENGINE SHUDDER/LOSS OF POWER DIAGNOSTIC & REPAIR PROCEDURE

#### VEHICLES AFFECTED: 1982-1985 Cadillacs Equipped With HT4100 Engines

Some 1982-1985 HT4100-equipped Cadillacs may exhibit a shudder and loss of power under slight acceleration or when climbing a hill. The service procedure outlined in this bulletin summarizes the diagnostic and repair information for this condition.

I. Perform the DFI System Check listed in Section 6E of the 1985 FWD-C Service Information Manual and repair as necessary.

II. Perform the 'Lack of Power, Sluggish, or Spongy' checks listed in section 6E of the 1985 FWD-C Service Information Manual and repair as necessary.

III. Review the listed Product Service Bulletins and repair as necessary.

#### Number Title

84-6-263 Poor Performance and/or Reduction of Power

85-6-191 Intermittent Reduction of Power or Engine Stops Running

Only after steps I through III have been reviewed, proceed to step IV.

IV. Engine mechanical repairs.

A. Remove cylinder heads and perform the following operations:

1. If the vehicle is a 1982-1984, or early 1985 with slotted cylinder head guide pins (refer to Product Service Bulletin 85-6-186, Group 6), replace the cylinder head guide pins with new stepped, tubular guide pins, (P/N 1634935). If it is a late 1981 with solid guide pins, they need not be replaced,

2. Remove and clean all valves; thoroughly clean the seats, guides, and cylinder heads. Do not remachine the valves or seats unless wear is evident.

3. Check the fit of the cleaned valves in the guides. They should not bind or stick.

4. Lube the valve stems with camshift pre-lube (P/N 992704).

5. Replace the valve stem seals and reassemble the heads.

B. Clean the intake manifold EGR passages.

C. Using new gaskets, reinstall the cylinder heads and intake manifold and reassemble the engine. Refer to the following Product Service Bulletins:

#### Number Title

83-6-198 HT4100 Intake Manifold 85-6-228 HT4100 Engine Revised Head Bolt Torque Procedure

D. Flush cooling system and add Cooling System Supplement (P/N 3634621).

E. Change engine oil and filter.

F. Start engine and warm to normal engine operating temperature. Run one can of Top Engine Cleaner through the throttle body per the instructions on the can (refer to Product Service Bulletin 85-6-137 in Group 6 to avoid catallitic converter damage), followed by one gallon of water according to the following instructions

1. Drill two 1.5mm (1/16 inch) holes in the bottom of an empty catalytic converter bead container (or equivalent) 60mm (2-1/2 inches) apart to correspond with the injector locations in the throttle body.

2. Fill the container with water.

3. Position the container over the throttle body and, while running the engine at 1500-2000 RPM, allow the contents of the battle to run into the throttle body bores.

G. Perform the ECR Valve Functional Test listed in the Service Information Manual.

For warranty purposes, when performing the procedure in step IV, use most applicable labour operation and time allowance as listed below.

#### Model Time ----- ---- 1982-1983 'C', 1984-85 'D' 8.8 1982-1985 'E/K' 8.3 1985-1986 'C' 10.1 1966 'E/K' 9.5

Add 1.0 hour if remachining the valves and valve seats.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.