Safari Van M V6-262 4.3L VIN W CPI (1992)
Technical Service Bulletin # 926A153
Date: 930401
PROM - Tick At Idle or Low Speeds/Detonation On Accel
BULLETIN NUMBER: 92-6A-153
SECTION: 6A
NUMBER: 3
CORPORATE REFERENCE NUMBER: 236111R
DATE: April 1993
SUBJECT:
CPI ENGINE NOISE (INSTALL NEW GEARS/NEW MEMCALS)
MODELS:
1992 S/T AND M/L VEHICLES WITH 4.3L ENGINE (RPO L35)
THIS BULLETIN CANCELS AND REPLACES GMC TRUCK SERVICE BULLETINS 92-6A-26 (CORP. # 176004) DATED DEC. 1991 AND
92-6A-101 (CORP. # 236111) DATED JULY 1992. THIS BULLETIN PROVIDES NOTICE OF THE 4.3L L35 ENGINE EXCHANGE PROGRAM
ENDING FOR 1992 MODEL YEAR VEHICLES, AS WELL AS ADDING AND REVISING GMSPO PART NUMBERS TO THE BULLETIN.
CHANGES HAVE BEEN MADE TO THE WARRANTY INFORMATION IN CONDITION 2. ALL COPIES OF GMC TRUCK SERVICE
BULLETINS 92-6A-26 AND 92-6A-101 SHOULD BE DISCARDED.
The 1992 model year 4.3L (L35) Engine Exchange Program is discontinued effective the end of December, 1992.
Condition and Cause of Noise
CONDITION
Some 1992 4.3L CPI engines may exhibit one or both of the following noises:
1.
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.
2.
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.
3.
If an engine has both noises (conditions "1" and "2"), follow condition "2" for cause and correction instructions and information.
CAUSE
1.
The most probable cause for the idle tick or rattle (condition # 1) 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.
2.
The source of the detonation or rattling type noise under acceleration between 2000-2500 rpm (condition # 2) 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 the Technical Assistance Center (TAC). 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.
Correction For Condition # 1
CORRECTION
1.
The following steps should be followed to correct an idle tick noise (condition # 1).
a.
Remove the accessory drive belt.
b.
Start the engine and note the noise. If it is still present proceed to step "c"; if not, proceed with diagnosis of accessory drive per the service
manual procedures.
NOTE:
Do not allow the engine to operate for an extended period of time with the accessory drive belt off. Remember the water pump and fan are
