From the AMC-list
MShumaker 
Matt in AZ. 

Yesterday, I offered to scan the appropriate 1983 TSM pages for the
peculiar method of setting the timing on the 1983 (and probably later)
258 engines. I got enough requests to warrant posting it. (Besides, I'll
be away for a while after surgery in the morning.) Rather than scan it,
the text that follows is transcribed from the 1983 TSM Supplement. Note
that the text refers to some supproting devices in the engine management
system, like the 4 inch Hg switch. 


The TSM Supplement text: 
  Ignition timing -- Six Cylinder Engine 
Primary Timing Procedure 
1. Set parking brake. Shift automatic transmission to Park, manual
transmission to Neutral. 
2. Start engine and allow to attain normal operating temperature. Ensure
that A/C is turned Off (if equipped). 
3. With ignition switch off, connect ignition timing light and properly
calibrated tachometer. 

NOTE: If the timing light has an adjustable advance control feature, 
turn the control to the OFF position. 

4. Disconnect vacuum switch assembly wire connector. 
5. Disconnect and plug distributor vacuum advance hose. 

WARNING: Use extreme caution when engine is operating. Do not stand in 
direct line with fan. Do not put hands near pulleys, belts, or fan. Do
not wear loose clothing. 

6. Start engine. 
7. Increase engine speed to 1600 rpm and check timing. If necessary,
adjust timing to specification listed on emission control information label. 
8. Tighten distributor holddown clamp and verify that ignition timing is correct. 
9. Turn off engine and remove timing light and tachometer. Connect No. 1
spark plug wire, if disconnected. Connect hose to distributor vacuum
advance mechanism. Connect wire connector to vacuum switch assembly. 

Alternate Timing Procedure 

This procedure does not require the engine speed to be increased to 1600 rpm. 
1. Set parking brake. Shift automatic transmission to Park, manual
transmission to Neutral. 
2. Start engine and allow to attain normal operating temperature. 
3. With ignition switch off, connect ignition timing light and properly
calibrated tachometer. 
NOTE: If the timing light has an adjustable advance control feature, 
turn the control to the OFF position. 
4. Disconnect the 4 in. Hg vacuum switch hose and plug opening. 

NOTE: The 4 in. Hg vacuum switch has black and red wires connected to it. 

5. Disconnect distributor vacuum hose and connect hose to 4 in. Hg
vacuum switch. 
6. Disconnect knock sensor wire connector and connect wire to cylinder
block (ground) with jumper wire. 

NOTE: Grounding the knock sensor wire prevents electromagnetic 
interference (EMI) from causing erroneous reactions by the
microprocessor unit (MCU). 

7. Start engine. 
WARNING: Use extreme caution when engine is operating. Do not stand in 
direct line with fan. Do not put hands near pulleys, belts, or fan. Do
not wear loose clothing. 
8. With engine at idle speed check timing. If necessary adjust timing
one (1) degree higher than specification listed on emission control
information label. 

NOTE: With the alternate timing procedure the basic timing must be one 
(1) engine degree higher than the specification listed on the emission
control information label. For example, if the timing specification is
listed as 6 deg. +/- 2 deg. at 1600 rpm, the alternate timing procedure
requires 7 deg. +/- 2 deg. at idle speed. 

************************************* 
JimBlair, Seattle,WA '83 Cher 4dr, '84 J10
**************************************