CANADIAN SERVICE MANUAL SUPPLEMENT REVISION

VEHICLES AFFECTED: 1985 'B' And 'G' Series Vehicles Equipped With 3.8L (VIN Code A) Engine

Attached is a revision to Pg. 6E2-14 of the 1985 Canadian Service Manual Supplement concerning changes to Spark/EGR/TCC T.V.S. parameters including activation temperature and port connections. Please affix the attached copy over Pg. 6E2-14 to update your manual.

Spark/EGR/T.C.C. T.V.S. Part Number 14079534

This thermal vacuum switch is used to control the vacuum signal to the Distributor, EGR and T.C.C. controls. The T.V.S. aids cold driveability by routing the vacuum signal through the distributor vacuum delay valve while blocking vacuum to the EGR and TCC controls below the activation temperature (43 DEG C/110 DEG F - EGR And TCC and 60 DEG C/140 DEG F - Distributor.

When the engine coolant reaches the TVS activation temperaure (60 DEG C/140 DEG F - Distributor) ports 3 to 4 open, allowing a direct manifold vacuum signal to pass through the TVS to the Distributor via the Distributor Vacuum Regulator Valve. Vacuum advance is not maintained during quick throttle openings thus reducing the possibility of ignition knock.

Blocked vacuum signal to the EGR valve ensures, during cold operation the combustion chamber receives complete charges of fresh air and fuel. When the activation temperature is reached, exhaust gases are recirculated through the combustion chamber to reduce emissions.

Port Connections:

Port 2 to carburetor ported vacuum source. Port 1 "leed" to EGR valve & TCC controls Port 3 to port 3 of Vac. Del valve Port 4 to port 2 of Vac. Del valve

Functional Tests:

1. Apply vacuum to port 1

a. Below 38 DEG C (100 DEG F) vacuum should hold (Port 1 to 2 closed)

b. At and above vacuum should pass unrestricted to port 2.

2. Apply vacuum to port 4

a. Below 54 DEG C (130 DEG F) vacuum should pass to vent (Ports 3 to 4 closed)

b. At and above 60 DEG C (140 DEG F) vacuum should pass unrestricted to port 3.

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.