Hummer H1 Service Manual page 131

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2-94 Engine
REPROGRAMMING TDC OFFSET
TDC offset must be reprogrammed whenever the PCM, front
cover, timing gears, timing chain, crankshaft position sensor,
or other components affecting timing are replaced. The proce-
dure for reprogramming TDC offset is as follows:
1. Verify that vehicle batteries are fully charged.
2. Start and run engine at curb idle speed.
3. Continue running engine at curb idle speed until coolant
reaches normal operating temperature.
4. Connect Tech 1 scan tool to data link/diagnostic
connector.
5. Select FO: OUTPUT TESTS from Miscellaneous Test
menu.
6. Select FO: INJ PUMP.
7. Select TDC OFFSET LEARN.
8. Press Up Arrow key and PCM will learn engine top dead
center offset value. This requires approximately 20
seconds.
9. Correct learned TDC Offset value should be between
minus 0.25 and minus 0.75. If value is not within specified
range, loosen injection pump and rotate it to correct value
as follows:
• If value is between plus 1.0 and minus 0.25, rotate pump
toward driver side to achieve specified value.
• If value is between minus 0.75 and minus 2.0, rotate
pump toward passenger to achieve specified value.
NOTE: 1 mm pump movement in either direction results in
approximately 2 degrees change.
+1.0 +.5 0 -.25
When the timing is in
this region, rotate pump
toward driver side to
achieve target zone.
-.75 -1.0 -1.5 -2.0
When the timing is in this
Target
region, rotate pump toward
Zone
passenger side to achieve
target zone.
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