This is part of the bulletin for the 92, don't assume this is the cause on your vehicle, but it could be.
It is very important to read the last section marked "Important" especially the last 2 sentences. GM says it isn't a reliability problem. (if this is the cause of the noise on your truck)
FILE IN SECTION: 6 - Engine
BULLETIN NO.: 23-61-11
DATE: June, 1995
SUBJECT:
CPI Engine Noise (Install New Gears/New MEM-CALs)
MODELS:
1992 Chevrolet and GMC Truck S/T, M/L Models
1992 Oldsmobile Bravada
with 4.3L CPI Engine (VIN W - RPO L35)
This bulletin is being revised to update engine scrapping information. Previous divisional publication numbers were:
Chevrolet 92-244B-6
GM of Canada 93-6A-121
GMC Truck 92-6A-153A
Oldsmobile 92-T-168
CONDITION
Some 1992 model year 4.3L CPI engines may exhibit one or both of the following noises:
I. A tick or rattle noise at idle or low engine speeds up to 1300 RPM. The noise may occur hot or cold in Park/Neutral or in gear.
II. A detonation or rattling type noise under acceleration at engine speeds between 2000 - 2500 RPM. It is usually most noticeable at the shift points under moderate acceleration with the transmission torque converter unlocked. Premium grade fuel does not affect the noise.
III. If an engine has both noises (conditions "I" and "II"), follow condition "II" for cause and correction instructions and information.
CAUSE
I. The most probable cause for the idle tick or rattle (condition I) is due to zero or near zero lash between the balance shaft drive gears. Some gears may feel as if the lash is acceptable but there is most likely an area on one of the teeth which is not meshing properly with the other gear.
II. The source of the detonation or rattling type noise under acceleration between 2000 - 2500 RPM (condition II) is the rear balance shaft needle bearing. With some engines, the rear needle bearing is excited by a combination of factors (i.e., engine case, combustion events, balance shaft gear lash, valve train torque reversals, cam chain play, needle bearing clearance, etc.).
Important: If there is any question about the proper diagnosis of the noise, call Technical Assistance. The unnecessary customer inconvenience and/or replacement of parts must be avoided. It is important to note that neither noise is a reliability or dependability concern. The noises are a customer pleasability issue only. The life of the engine will not be shortened due to the above causes.
