"<.i>Bruce can you clarify again what goes where? There is a green wire from the O2 sensor to the ECU. It is connected to the O2 sensor via standard male/female solderless terminals.

If the disconnected terminal from the O2 sensor is put on the battery how is any signal transmitted to the ECU because the sensor wire has been disconnected?"

Ian,
Sorry this abbreviated version of my canned post wasn't clear. In both tests, the meter is monitoring the disconnected sensor lead, while the ECU lead is subjected to simulated (extreme) lean or rich faked O2 signals.

Here is the original write up...

O2 Sensor/ECU Rich-Lean Test

This test is described in the the Bosch FI & Engine Management manual (p 6-22, "Rich stop" and "Lean Stop"), for Continuous Injection (CI) K-jet, and is also described as being applicable to LH injection in the Volvo Problem Solver. I have used it on both systems, and offer it here as a way to verify the sensor/ECU responses.

O2 sensor/ECU interaction can be tested by sending simulated Full RICH and Full LEAN O2 sensor signals to the ECU, and watching for appropriate responses from the O2 sensor. This is done "Open Loop", (i.e., with the O2 sensor signal unplugged), and with Voltmeter connected to the O2 sensor lead. The engine and O2 sensor should be fully warmed up for this test.

Full Rich Test: Apply a + voltage potential to the ECU Green wire. Use either the + terminal of a grounded 1.5 volt (Flashlight) battery. Or, if you have Orangutan arms, hold the ECU (green wire) terminal with one hand and put the other hand on the Battery Positive terminal. The ECU should see this as a "Rich" O2 signal and respond by setting a very lean fuel mixture. The Idle should worsen (may even stall), and the O2 sensor should respond with a correspondingly low output (0.1 to 0.2 volts), as the ECU leans out what it believes to be a "rich" mixture.

Full Lean Test: Ground the Green wire going to the ECU (I use the braided ground on the valve cover). This simulated "O2 Lean" signal should result in very rich "corrective" mixture setting from the ECU . The RPMs should increase, and the O2 sensor output should rise to nearly a full 1.0 volt.


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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.