Coupe L4-1.9L DOHC VIN 7 (1994)
Technical Service Bulletin # 91-T-36B
Date: 931101
Vehicles Affected and Defect Description
NO.: 91-T-36B
DATE: November, 1993
GROUP: Engine
CORP. NO.: 180106R
SUBJECT:
Excessive Vehicle Noise and/or Vibration (Check Powertrain Mounts, Exhaust, and/or Cooling System)
Due to the following revisions, this bulletin supercedes bulletin 91-T-36A, which should be discarded.
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Addition of 1993 and 1994 vehicles.
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Revisions to affected model years under "CAUSE".
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Addition of a new step in ENGINE STRUT CRADLE BRACKET.
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Revised part number in step 4 of INTERMEDIATE EXHAUST PIPE ISOLATOR and under "PART REQUIREMENTS".
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Revisions to model years throughout bulletin.
MODELS AFFECTED:
1991-1994 Saturns
CONDITION:
Some owners of 1991-1994 Saturns may comment on objectionable vehicle noise and/or vibration levels observed in the steering wheel, seat and/or floor
pan.
CAUSE:
Objectionable vehicle noise and/or vibration may be caused by:
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Preloaded powertrain mounts (1991 vehicles)
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Preloaded engine strut cradle bracket or cradle misaligned to body (1992-1994 vehicles)
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improperly positioned/worn exhaust system isolators and muffler band clamp/block (1991-1994 vehicles)
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Lower cooling module grommets, improper positioning of wiring harnesses and upper cooling system module grommets (1991-1994 vehicles)
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Improper routing of A/C hoses or deaeration hoses, hood release cable and air inlet snorkel (1991-1993 vehicles)
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Debris in accessory drive belt pulleys (1991 vehicles)
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Improper adjustment of hood stop(s) (1991-1994 vehicles)
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PCV or brake booster check valve noise (1991 vehicles)
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DOHC (LLO) automatic transaxle mount assembly replacement (1991 vehicles)
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Malfunction of engine electrical/fuel system (1991-1994 vehicles)
CORRECTION:
Before attempting repairs, please review the following vehicle noise and vibration information.
VEHICLE NOISE AND VIBRATION
Four-cycle engines have a second-order firing frequency. This means that it takes two, complete crankshaft revolutions to fire all cylinders or one
crankshaft revolution to fire one-half of the cylinders. Because of the way the cylinders are fired, an engine disturbance is created due to cylinder
pressures or pulses. Most engine disturbances are absorbed by the powertrain rubber isolation mounts. Depending on the isolation package, some of this
disturbance may be transmitted into the body structure and felt inside the vehicle when stopped, with the engine running and/or under certain driving
conditions. These conditions are natural in most vehicles.
Vibrations are normally felt in the steering wheel, lower seat cushion, seat back or floor pan. Vibrations are diagnosed with the vehicle stopped and the
transaxle in (D) Drive and/or (R) Reverse for automatic transaxles, and in Neutral for manual transaxles. If the vehicle is equipped with A/C, the A/C
should be On or Off depending on the instruction given in the diagnosis step.
IMPORTANT:
Before performing the following procedures, the vehicle should be road tested and the complaint verified with the engine at operating temperature.
Engine misfire complaints are usually easy to detect during a short road test and must be corrected prior to evaluating a vibration and/or noise
concern.
NOTE:
Minimum Idle Speed (TBI-MFI) adjustments are set at the factory and MUST NOT be tampered with to alter minimum or maximum engine idle
speed. Improper adjustment of the idle speed screw can cause false PCM codes, idle instability and automatic transaxle shift concerns, etc.
Perform the following steps in order to decrease vehicle noise and/or vibration.
