General Motors — Determining the Master/Slave Engine Positions
Operation · Sync/Cruise system
From a General Motors owner's manual covering: Carb 5.7L, MP 5.0L, MP 5.7L, MP 6.0L. Check it applies to your exact model before use.
Procedure
- Ensure the Syn/Cru Mode switch is in the OFF position.
- Perform the engine starting procedure for both engines; idle in neutral.
- Press the Syn/Cru Mode switch to ON; the Sync Lamp should blink or be steady ON.
- Starting with the Port engine, slowly push each throttle forward one at a time and note which throttle increases engine RPM.
- Place the throttle that does NOT increase RPM in the wide-open-throttle position.
- Move the throttle that does increase RPM forward slowly and observe that both engines increase in RPM; this engine is the Master.
- Return the throttle handles to Idle/Start, then place the Syn/Cru Mode Switch to OFF.
Source: General Motors owner's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.