LACK OF POWER, ENGINE SURGE, VIBRATION OR ROUGHNESS

MODELS AFFECTED: 1982-96 ELDORADOS, SEVILLES, DE VILLES, BROUGHAMS AND FLEETWOODS EQUIPPED WITH AN HT4100 ENGINE

Some Cadillac vehicles equipped with HT4100 engines may experience a lack of power condition and/or other driveability conditions (engine surge, vibration or roughness) due to an out-of-time camshaft. A simplified test procedure has been developed to check for a misindexed camshaft. This procedure eliminates the need to remove the front cover to examine the cam sprocket to crank sprocket relationship.

If a misindexed cam is suspected, the following steps should be performed:

1. Remove the left rocker arm cover.

2. Remove the Left Rocker Pivot Support Bar assembly following recommended Service Manual procedures.

3. Turn the engine over in a clockwise direction by hand (removing the spark plugs may make it easier to turn the engine over) until the No. 1 piston is beginning the exhaust stroke. The piston will be near BDC and both valves will be closed. At this time, the front crankshaft pulley timing notch will be approximately 180 DEG from the front cover timing indicator.

4. Install a dial indicator at the top of the intake push rod as shown in Figure 1. Zero the dial indicator.

5. Turn the engine over slowly by hand until a dial indicator reading of .004" is obtained.

6. Examine the crankshaft pulley timing notch. The notch should read 20 DEG BTDC (refer to Figure 2). If any variation greater than +/- 2 DEG is observed, the camshaft may be misindexed. Remove the front timing chain cover and cam sprocket and inspect for the following items (refer to Figure 3):

- Worn cam sprocket dowel pin hole. - Worn cam or crank sprocket teeth or timing chain. - Proper cam sprocket to crank sprocket relationship. - Loose cam sprocket bolt. - Loose or missing cam dowel pin. - Worn or missing crankshaft key.

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.