Chevrolet 10 Series 1970, Руководство по обслуживанию

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ENGINE 6-11
m echanical drag in engine.
Uneven cranking speed—Uneven com pression,
d e fective sta rte r to s ta rte r d riv e .
Ignition Switch
W ith vo ltm e te r connected as d escrib ed fo r the Cranking
V oltage T e s t, turn ignition switch to ON. V oltage should
drop to 5 to 7 vo lts as current is now passing through
high resista n ce w ire connected between ignition switch
and (+) p o sitive term in al o f co il. If battery voltage o f
12 v o lts is obtained, the sta rte r solenoid is by-passing
the high resistan ce w ire connected between ignition
switch and (+) p o s itiv e term in al o f co il, thus the sta rter
solen ois is not functioning p ro p e rly to by-p ass the ig n i­
tion resista n ce w ire o r the ignition c ircu it is in c o rre c tly
w ired .
NOTE: The voltage drop (12 to 5-7 v o lts) w ill
only take place when the points a re closed. If
the points a re open, the path through the r e s is t­
ance w ire w ill not be com pleted.
Distributor Resistance
Use equipment as d irected by m anufacturer. E x cessive
resista n ce in p rim a ry circ u it must be elim inated b efo re
continuing with test p rocedu re.
Secondary Resistance
Use equipment as d irected by m anufacturer.
• U n iform “ norm al readings” as sp ecified by manu­
fa ctu rer indicate a ll secondary c ircu it components
a re in good condition.
• If all readings a re “ below n o rm a l/ ’ check fo r c o r ­
roded c o il lo w e r term in a l, p o o rly connected or
broken c o il w ire , center cap e lectro d e o r ro to r tip
burned, o r an open secondary in co il.
• If readings a re “ higher than n orm al” at two o r m ore
plugs adjacent in firin g o rd e r, c ro s s firin g is o c c u r­
rin g in distribu tor cap o r between spark plug cables
concerned.
• If m eter reads o ff scale to le ft, the c o il p o la rity is
re v e rs e d . Check fo r r e v e rs e d c o il p rim a ry w ire s ,
w rong c o il o r re v e rs e d veh icle battery connections.
Ignition O utput and Secondary Leakage
Use equipment as d irected by m anufacturer.
• GOOD readings indicate both ignition output and
secondary insulation a re good.
• If all readings a re BAD o r if ignition test ca lib ra to r
cannot be adjusted to Set Lin e, check fo r high r e s is ­
tance in p rim a ry circu it, d efective distribu tor points,
c o il o r condenser.
• If readings a re BAD when certain plug w ire s a re
lifte d off, check fo r crack s o r carbon tracks in d is ­
tribu tor cap o r d efective insulation on those plug
w ire s being lifte d off.
Carburetor
R e fe r to Section 6M to p e rfo rm adjustments such as
id le vent, float le v e l, pump rod and vacuum break.
Fuel Pump
If the owner has com plained o f poor high speed p e r ­
form an ce, the fuel pump may be at fault. T oo low a
pump p ressu re o r volum e w ill cause a high speed “ m is s ”
because o f lack o f fuel d e liv e re d to the carb u retor,
w hile too high a p ressu re w ill cause carbu retor flooding.
Check fuel pump as outlined in Section 6M.
Cooling System
The follow in g test may be p erfo rm ed with p ressu re
testing equipment availab le c o m m e rc ia lly fo r this pu r­
pose. T h is test p ro v id e s an excellen t means o f detecting
internal o r extern al leaks within the cooling system .
1. Rem ove rad iator cap.
F ig . 2 0 —Testing C ra n k in g V o lta g e F ig . 2 1 —C o o lin g System Pressure Test
CHEVROLET TRUCK SERVICE MANUAL