Engine - Knock Diagnosis
89pontiac15Bulletin Number: 89-6-64
Reference Number: 936119R
Publish Date: 8/89
Subject: ENGINE KNOCK DIAGNOSIS (NOISES)
Models: 1988-89 6000, GRAND AM AND FIERO MODELS WITH 2.5L (VIN CODES U AND R) AND AUTO
Affected: TRANSMISSION
Customer comments may be received regarding engine knock or rattle noises on the following vehicles:
1988-89 Grand Am models with 2.5L engine (VIN Code U) 1988-89 6000 models with 2.5L engine (VIN Code R) 1988 Fiero models with 2.5L engine (VIN Code R)
Usually, this noise is evident only on vehicles equipped with automatic transmissions. This bulletin provides guidelines which may be used to distinguish between camshaft timing gear knock/rattle noise and force balancer gear knock/rattle noise. These noises sound very similar to one another under certain operating conditions and isolating the source may be difficult.
The chart below illustrates the engine and transmission operating conditions at which force balancer gear or the camshaft timing gear knock/rattle noise is noticeable.
ENGINE OIL TEMPERATURE
HOT COLD
TRANSMISSION FORCE BALANCER
IN GEAR CAM GEAR
CAM GEAR
TRANSMISSION CAM GEAR CAM GEAR
PARK/NEUTRAL
* If the knock/rattle noise occurs cold, it is not the force balancer.
* If the knock/rattle noise occurs with the transmission in park/neutral, it is not the force balancer.
In order to determine which system is causing the noise, shift the transmission into gear - if the knock/rattle noise becomes evident, the noise is most likely force balancer related.
IMPORTANT: IF THIS IS THE CASE, REPLACEMENT OF THE FORCE BALANCER AND/OR CRANKSHAFT WILL NOT CORRECT THE CONDITION.
The knock/rattle condition is caused by the particular way that the teeth of the large crankshaft gear and the small balancer intermediate gear mesh together. This noise will produce no detrimental effects to the engine.
If the knock/rattle noise is not force balancer related, further diagnosis per the Service Manual is recommended to correct the condition.