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ENGINE ELECTRICAL
6D-29
temperature is above approximately 1 15°F. and full manifold
vacuum is applied to the distributor. The TVS also controls
the secondary vacuum break on California and High Altitude
Certified Vehicles and is called a SVB/BS-TVS. Service of the
secondary vacuum break portion of the valve is in Section 6C.
L4-15 1 Engine
The L4-151 engine is equipped with a vacuum delay
valve, VDV, to maintain vacuum advance during quick
throttle openings when the engine coolant temperature is
below approximately 120°F. This feature improves engine
response during cold engine operation. The VDV is by-passed
thru distributor spark TVS when the engine coolant
temperature is above approximately 120°F. Above 120°F.
coolant temperature full manifold vacuum is used for
distributor spark except for L4-151 engine with air
conditioning and automatic transmission, which uses ported
vacuum.
V6-231 Engine
V6-231 Engines, except California, use full manifold
vacuum for distributor spark with no vacuum conttols. V6
231 California engines with automated transmissions use
ported vacuum for distributor spark, with no vacuum
controls. V6 23 1 California engines with manual transmission
use ported vacuum with Transmission Controlled Spark,
TCS. TCS applies vacuum to the distributor in 3rd gear on
A, F and X Series and 4th and 5th gear on HM Series.
V8-301 Engine
V8-301 engines with manual transmission use ported
vacuum for distributor spark. No vacuum controls are used.
V8-301 engines with automatic transmission without air
conditioning use full manifold vacuum for distributor spark.
No vacuum controls are used.
V8-301 engines with automatic transmission and air
conditioning use a full time vacuum modulator valve, VMV,
with a vacuum delay valve, VDV, to maintain vacuum
advance during quick throttle openings when the engine
coolant temperature is below approximately 120°F. This
feature improves engine response during cold engine
operation. The VDV is by-passed thru the distributor spark
TVS when the engine coolant temperature is above
approximately 120°F., and the distributor spark vacuum is
regulated only by the VMV. The VMV limits the distributor
spark vacuum to a calibrated value until ported vacuum
applied to the control port of the VMV is greater than the
calibration valve. When ported vacuum is greater than the
calibration value, the distributor spark vacuum is equal to
ported vacuum.
V8-350 and 4 0 0 Engine, VIN Code P &
Z
V8-400 engines with manual transmission use port
vacuum for distributor spark with a coolant overheat TVS
which provides full manifold vacuum to the distributor when
the engine coolant temperature is above approximately 225°F.
V8-350 and 400 engines, VIN Codes P &
Z,
with
automatic transmission, are equipped with a spark retard
delay orifice to maintain vacuum advance during quick
throttle openings when the engine coolant temperature is
below approximately 120°F. This feature improves engine
response during cold engine operation. The spark retard delay
orifice is by-passed thru the distributor spark TVS when the
engine coolant temperature is above approximately 120°F.
and full manifold vacuum is applied to the distributor.
V8-350 and 4 0 3 Engines, VIN Codes R & K
Low Altitude Certified Vehicles
Low altitude certified V8-350 and 403 engines, used in
early production B cars only, use full manifold vacuum for
distributor spark. The engines are equipped with a distributor
spark vacuum reducer valve, DS-VRV, which reduces the
vacuum applied to the distributor by 1.5 inches of mercury
when engine coolant temperature is above approximately
220°F. The DS-VRV is by-passed by the distributor spark
TVS
when
engine
coolant
temperature
is
below
approximately 220°F.
California Certified Vehicles
California certified V8-350 and 403 engines use ported
vacuum for distributor spark. The ported vacuum is
controlled by an EGRIDS-TVS, DS-TVS, and a distributor
spark VDV. The EGR/DS-TVS prevents any vacuum
advance when the engine coolant temperature is below
approximately 120°F. The DS-TVS applies full manifold
vacuum to the distributor when the engine coolant
temperature is above approximately 220"F., for engine
overheat protection. The DS-VDV delays the application of
vacuum to the distributor when throttle opening is reduced,
such as after vehicle acceleration. The DS-VDV is unaffected
by DS-TVS operation.
High Altitude Certified Vehicles
High altitude certified V8-350 and 403 engines use
ported vacuum for distributor spark. The engine is equipped
with a DS-TVS which applies full manifold vacuum to the
distributor when the engine coolant temperature is above
approximately 220°F., for engine overheat protection.
DIAGNOSIS
H.E.I. DISTRIBUTOR
Use Figure 6D-38 for H.E.I. Diagnosis. This diagnosis
will cover both H.E.I. ignition systems, either internal or
external coil.
SPARK PLUGS
Worn or dirty plugs may give satisfactory operation at
idling speed, but under operating conditions they frequently
fail. Faulty plugs are indicated in a number of ways: poor fuel
economy, power loss, loss of speed, hard starting and general
poor engine performance.
Spark plug failure, in addition to normal wear, may be
due to carbon fouled plugs, excessive gap or broken insulator.
Fouled plugs may be indicated by checking for black
carbon deposits. The black deposits are usually the result of
slow-speed driving and short runs where sufficient engine
operating temperature is seldom reached. Worn pistons,
rings, faulty ignition, over-rich carburetion and spark plugs
which are too cold will also result in carbon deposits.
Excessive gap wear, on plugs of low mileage, usually
indicates the engine is operating at high speeds or loads that
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