G420E/G424E
Tier
LP Engine
Test And Adjustments
82
Ignition Timing Adjustment
With the MI-04 system both mechanical and vacuum
advance are no longer inside the distributor. All
ignition timing advance is controlled by the SECM.
The only timing adjustment that can be made by a
technician is the mechanical alignment of the
distributor. The SECM uses a 40-degree timing
window from –5 degrees BTDC to 35 degrees BTDC.
Because of this an accurate adjustment cannot be
made with a standard timing light since the SECM will
maintain the correct timing even if the distributor is
moved (as long as the distributor setting remains
within the 40-degree window). Therefore the ignition
timing setting of the distributor becomes very
important and is described in the following steps.
1.
Using the timing indicator on the crankshaft pulley,
set the engine on 0 degrees Top Dead Center
(TDC) of number 1 cylinder (Figure G1).
2.
Remove the distributor rotor cap and verify that
the
distributor rotor is lined up with number 1
cylinder on the distributor cap (Figure G2).
3.
Remove the distributor rotor and dust cover so
that the internal VR sensor and signal rotor gear
are visible (Figure G3). The internal VR sensor
inside the distributor is not used by the SECM for
a speed reference with the G420E/G424E engine
and it’s wiring harness does not connect to the
system. The distributors internal VR sensor is only
used as an alignment reference point for setting
the correct distributor position.
Figure G1
Figure G2
Timing Wheel at 0
degrees TDC
View of Distributor Rotor Cap
#1 Cylinder
Distributor with Rotor Cap Removed
Firing Order
1-3-4-2
Distributor View of Internal VR Sensor
Internal
VR Sensor
Signal
Rotor
