Connecting Dwell Meter
- A dwell meter set on "6-cylinder" scale for all engines is used to measure ECM output and M/C dwell (duty cycle). A green connector located in wiring harness near carburetor is the dwell meter connection point.
Courtesy of GENERAL MOTORS COMPANY
- When dwell meter is connected, do not allow terminal to touch any ground source, including hoses. This could damage ECM. On a normal operating engine, dwell at both idle and part throttle should read between 10-50° and will be varying. "Varying" means needle will continually move up and down the scale. The amount of variation does not matter, only fact that it does move.
- This variation of needle indicates system is in closed loop and ECM is responding to signals from oxygen sensor. At wide open throttle or cold engine operation, dwell will be fixed (needle steady). This indicates open loop and that ECM is ignoring oxygen sensor signals.
- If there is doubt whether engine is in closed loop or open loop, richen or lean mixture (choke carburetor or cause air leak). This action will cause dwell to change if engine is in closed loop.