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As a follow-on to my post below questioning that new O2 sensor, here is a "canned post" I drag out now and then...
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).
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 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.
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