CISreadings

Whacked-Out Duty Cycle Readings?

The two tables below contain readings on a 1986 CIS Cabriolet. The initial test readings in attempts 1 and 2 point to a possible control unit issue and/or meter issue (one reason a new meter was bought). However, tests 3-5 prove that while the readings are bizarre, the idle changed as did the meter readings, which indicates the control unit is good as well as the meters (meters were double-checked using the green/white Hall generator wire). The thermoswitch was proven good after conducting a resistance test. The frequency valve buzzes every time the engine runs and the engine purrs like a kitten. The components as well as the meters all indicated, if not proved to be good. So, in the name of science...

Hypothesis: Test port is faulty, which was suspected at the very start.

Experiment: The OEM probe harness was cut off and spade terminals were crimped onto the wires in order to provide a better contact using alligator clip adapters on the meter probes. The tests were then conducted for a third time.

Result: As can be seen in the Attempt #3 table, the test port was indeed faulty (not providing good enough probe contact).

Conclusion: The OEM probe test port is garbage!

Attempt #1 (dwell meter)
Test	Oxygen Sensor	Full-throttle Switch	Oxygen Sensor Thermoswitch	Running Condition/Stage	Dwell Reading Should Be...	Your Reading
Warm-up	Connected	Connected	Connected	cold-running enrichment	72° ±2°	84°
Operating Temp	Connected	Connected	Connected	closed-loop	45° ±7°	84°
1	Connected or Disconnected	Connected	Disconnected	open-loop	45° ±2°	84°
2	Connected	Connected & actuated	Disconnected	full-throttle enrichment	58.5° ±2°	84°
3	Connected	Connected	Disconnected, leads bridged w/ jumper wire	cold-running enrichment	72° ±2°	84° w/ slight idle drop
4	Disconnected, ECU lead grounded	Connected	Disconnected	lean condition, rich correction (closed loop)	78.3° and increasing	65° & decreasing
5	Disconnected, +1.5V applied to ECU lead, -1.5V grounded	Connected	Disconnected	rich condition, lean correction (closed loop)	18° and decreasing	42° & decreasing w/ slight idle drop

Attempt #2 (brand new duty cycle meter)
Test	Oxygen Sensor	Full-throttle Switch	Oxygen Sensor Thermoswitch	Running Condition/Stage	Duty Cycle Reading Should Be...	Your Reading
Warm-up	Connected	Connected	Connected	cold-running enrichment	80% ±2%	76-98%, fluctuating
Operating Temp	Connected	Connected	Connected	closed-loop	50% ±8%	76-98%, fluctuating
1	Connected or Disconnected	Connected	Disconnected	open-loop	50% ±2%	70-98%, fluctuating; 58% avg. high after fan cycled
2	Connected	Connected & actuated	Disconnected	full-throttle enrichment	65% ±2%	90-98%, fluctuating
3	Connected	Connected	Disconnected, leads bridged w/ jumper wire	cold-running enrichment	80% ±2%	89-98%, fluctuating w/ slight idle drop
4	Disconnected, ECU lead grounded	Connected	Disconnected	lean condition, rich correction (closed loop)	87% and increasing	rose to 53.7% and stopped
5	Disconnected, +1.5V applied to ECU lead, -1.5V grounded	Connected	Disconnected	rich condition, lean correction (closed loop)	20% and decreasing	dropped to 91.2% w/ slight idle drop

Attempt #3 (using new spade test terminals)
Test	Oxygen Sensor	Full-throttle Switch	Oxygen Sensor Thermoswitch	Dwell Reading Should Be...	Your Reading	Duty Cycle Reading Should Be...	Your Reading
Warm-up	Connected	Connected	Connected	72° ±2°	67.8°	80% ±2%	50% (car is in a warm climate)
Operating Temp	Connected	Connected	Connected	45° ±7°	(measured & adjusted using duty cycle)	50% ±8%	15% (running rich)
1	Connected or Disconnected	Connected	Disconnected	45° ±2°	42°	50% ±2%	50%
2	Connected	Connected & actuated	Disconnected	58.5° ±2°	55°	65% ±2%	65%
3	Connected	Connected	Disconnected, leads bridged	72° ±2°	67.8°	80% ±2%	80%
4	Disconnected, ECU lead grounded	Connected	Disconnected	78.3° and increasing	78.3°+	87% and increasing	80%+
5	Disconnected, +1.5V applied to ECU lead, -1.5V grounded	Connected	Disconnected	18° and decreasing	(ground connection unavailable)	20% and decreasing	(ground connection unavailable)