Pontiac Fiero 1988 Service Manual page 415

6D4-2 IGNITION SYSTEM
(EST) HEI DISTRIBUTOR
Fig. 1 HEI (EST) Distributor
the crankshaft reluctor ring. Notches in the crankshaft
reluctor ring tigger the magnetic pickup sensor to
provide timing information to the ECM. The magnetic
pickup sensor provides a cam signal to identify correct
firing sequence, and crank signals to trigger each coil
at the proper time.
This system uses EST and control wires from the
ECM, as with distributor systems. The ECM controls
timing using crankshaft position, engine rpm, engine
temperature, and manifold absolute pressure (MAP)
sensing.
Further EST information is found in Sections
6E2 and 8A.
Ignition T i m i n g
Timing specifications for each engine are listed in
Section 6E. When using a timing light, connect an
adapter between the No. 1 spark plug and the No. 1
spark plug wire, or use an inductive type pick-up. Do
n o t p i e r c e t h e p l u g l e a d .
Once the insulation of the
spark plug cable has been broken, voltage will jump to
the nearest ground, and the spark plug will not fire
properly.
A l w a y s f o l l o w t h e t u n e - u p l a b e l
p r o c e d u r e s w h e n a d j u s t i n g t i m i n g .
Some engines will incorporate a magnetic timing
probe hole for use with special electronic timing
equipment. Fig. 1A shows a typical magnetic probe
hole. Consult manufacturer's instructions for use of
this equipment.
520003-6D
Fig. 1A Magnetic Timing Probe Hole
Secondary Wiring
The spark plug wiring used with ignition systems
is a carbon impregnated cord conductor, encased in an
8MM (5/16") diameter silicone rubber jacket. The
silicone jacket withstands very high temperatures and
also provides an excellent insulator for the higher
voltage of the HEI system. Silicone spark plug boots
form a tight seal on the plug.
The boot should be
twisted 1/2 turn before removing.
Care should
also be exercised when connecting a timing light or
other pick-up equipment. Do not force anything
between the boot and wiring, or through the silicone
jacket. Connections should be made in parallel using