Two distinct phases are involved in a complete prelubrication cycle. The two phases are:
1. Prelubrication Phase- Begins when the key switch is held in the START position. A circuit is provided to
ground through the normally closed pressure switch. The circuit is interrupted upon opening of the pressure
switch when the prelube pressure reaches 2.5 psi (17.2 kPa).
2. Delay and Crank Phase- Begins when the pressure switch opens. A 3 second delay precedes the crank
mode.
• Starter prelubricates only. Does not delay or crank. Indicates oil pressure is not sufficient to open the pres-
sure switch.
a. No oil or low oil in engine. The pump can not
build sufficient pressure to open switch.
b. Pump failure.
c. Pressure switch has failed (closed) and is
grounding circuit.
d. Oil pressure switch wire chafed and shorting to
block.
• Starter prelubricates continuously regardless of
key switch position.
Indicates Prelube Timer Solenoid contacts have
welded.
a. Low voltage can cause relay failure.
b. Jump starting of the vehicle with a voltage that
is higher than was designed for the system,
can cause solenoid contacts to weld.
• Starter delays and cranks. No prelubrication mode. If an operator indicates the ignition is totally dead,
make certain the key is being held in the crank position
for 3 to 4 seconds. If the engine cranks after a short
delay, this indicates that a ground connection to the
pressure switch has been broken. Without a ground
path, the prelubrication unit will proceed to delay and
crank.
a. Check the wire to the pressure switch. If the
wire is removed or cut, replace it.
b. Check the ground strap to engine block. If the
ground strap is missing the block is not
grounded.
c. Check the pressure switch for an open circuit.
Remove the wire, then check for an open cir-
cuit between the switch terminal and the
switch base. If open, replace the pressure
switch.
Problem Probable Cause
• Starting circuit is irregular when in crank mode. a. Check for low or dead batteries.
b. Check alternator output.
c. Check ground connection at “G” terminal of
starter bendix solenoid.
d. Check for defective starter safety relays.
e. If everything checks OK, replace batteries.
NOTE: Maximum allowable voltage drop is - 2
volts for starter control circuit.
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