For 1990-2009 cars

# ENGINE SHUDDER & LOSS OF POWER DIAGNOSTIC & REPAIR PROCEDURE

#### MODELS AFFECTED: 1985-1987 DE VILLES AND FLEETWOODS 1982-1987 ELDORADOS AND SEVILLES 1982-1985 RWD DE VILLES AND BROUGHAMS

This Bulletn supersedes T-86-23, Group 6E, Number 24, which should be destroyed. Some 1982-1987 HT4100-equipped Cadillacs may exhibit a shudder, vibration, and/or loss of power under slight acceleration or when climbing a hill. The shudder condition may be more apparent with TCC engaged. 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 DeVille and Fleetwood Service Information Manual and repair as necessary.

II. The following procedure is used to check for exhaust valves momentarily sticking open. Top Engine Cleaner (TEC) is used to clean engine deposits from exhaust valve stems. GM Part Numbers 1050002, 1052626 or their equivalents, may be used for this process.

Although TEC does not affect catalyst performance when used as directed, misuse of the product may result in appreciable losses in catalytic converter efficiency due to high temperatures caused by the extra rich mixture. For this reason TEC must be used according to its label with particular attention to the following:

1. Allow the engine to run at idle for 10 to 15 minutes before adding TEC.

#### NOTE: This will allow the converter to stabilize at a lower temperature and, thus, minimize the chance of thermal degradation upon introduction of TEC into the system.

2. Remove air cleaner assembly.

3. Divert the AIR from the converter in the following manner:

Longitudinal HT4100 Models: Open the set-timing connector.

Transverse HT4100 Models: Electrically disconnect the AIR divert solenoid (connector with two pink/black wires).

4. Pour half a can of TEC into throttle body at a slow, steady rate with engine idling.

5. Pour remaining half can of TEC into throttle body at a fast enough rate to stall engine. Let TEC soak in engine a minimum of six hours.

6. Start engine and idle 10 to 15 minutes. Increase engine speed to 2,000 rpm. Pour another can of TEC into throttle body at a slow, steady rate so that engine does not stall.

7. Restore AIR management system functions as follows:

Longitudinal Models: Reconnect the set-timing connector.

Transverse Models: Electrically reconnect the AIR divert solenoid (connector with two pink/black wires).

If the TEC cleaning procedure improves or eliminates the engine shudder/vibration condition, proceed to Step IV.

III. Review the listed Serviceman Bulletins and repair as necessary:

Number Group Title ------ ----- ----- T-83-25 6D Engine Performance Diagnosis - HEI Ignition System T-85-35 6E Poor Performance and/or Reduction of Power T-85-71 6D Intermittent Reduction of Power or Engine Stops Running T-86-22 6E Lack of Power, Engine Surge, Vibration or Roughness

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 Serviceman Bulletin T-85-73, Group 6A), replace the cylinder head guide pins with new stepped, tubular guide pins, P/N 1634935. If it is a late 1985, 1986 or 1987 with solid guide pins, they need not be replaced.

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

3. Replace exhaust valves with exhaust scraper valve kit, P/N 3634759, for standard size guides and P/N 3634760 for .003" oversize. The kit includes 8 exhaust valves and 16 keys.

4. Check the valve stem to guide clearance on all valves. They should not bind or stick. Repair or replace as necessary.

5. Lube the valve stems with camshaft pre-lube, P/N 1052365.

6. Reassemble the heads using new valve stem seals, P/N 1622249 for 1982-1986 vehicles, and P/N 1641440 for 1987 vehicles.

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 Serviceman Bulletins:

Number Group Title ------ ----- ----- T-83-104B 6A HT4100 Intake Manifold T-85-93 6A HT4100 Engine Revised Head Bolt Torque Procedure

For warranty purposes when performing the procedure in Step IV, use Labor Operation number T6137 for the applicable time allowances listed below:

#### Model Time ----- ---- 1982-1983 "C", 1984-1985 "D" 8.8 1982-1985 "E/K" 8.3 1985-1987 "C" 10.1 1986-1987 "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.