i am testing the functionality of my o2 in 91 740wgn non turbo.according to the process in the brickboard .when key is set to start position (engine off)it should read battery voltage at heater power wire(red).i don't see any voltage drop until the car is running.it does the same in my 93 940 sedan.also when probing the signal wire(white) and sig return(green) the voltage fluctuate
between .01 and 1.1V,but when i remove the vaccum line to FPR or create a vaccum leak the reading stays always the same.does any one have a detailed info on how to test o2 sensor?i am doing this because i am getting bad gas miles(16 to 17mil/gal)(10%ethanol in gas) here in new england.all tune up is done,tire presure,gas filter,new breaks and calipers.cleaned and adjusted throtel and intake (no vaccum leaks),still need to clean injectors,and probably try another temp sensor.thanks

sorry for the confusion.both the 940 and 740 have the regina system.the black
wire from the O2 is connected to the Green wire in the car harness(and thats what i was refering to).i have the 740 for 3 years now,i never changed the O2.
i am using a voltmeter so the fluctuation is fast but not sure I need to use
an asciloscope but do have one.my main concern is why there is no change in the reading when i pull the vaccum to the fpr and also when i cause a vaccum leake in the system.thanks

"...my main concern is why there is no change in the reading when i pull the vaccum to the fpr and also when i cause a vaccum leake in the system.thanks"

• OK then. I did notice that your voltage readings match what's specified for the Titania sensor.

But I question that vacuum test. Sure it causes an air leak, but also lets the FPR "see" atmospheric pressure, as with Wide Open Throttle—so it raises the fuel pressure about 9 psi, which tends to richen the mixture.

I don't know if that rise in pressure is enough to offset the induced vacuum leak. But if that test is from the same source that thought you could test the 02 heater with the engine off, it's grain of salt time.

As long as your 02 is switching rapidly between thos voltage levels, I'd say it's doing the job.

It's possible to "force" stronger rich and lean signals to the ECU, and watch the (unplugged) sensor to see if it responds accordingly. Post back if you want my canned blurb on that.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

thanks bruce for all.yes if you know of a better way to test O2 i would like to try it.thanks

Here it is, with two caveats:

1) I don't believe I've done it on the Regina FI, but see no reason it should be any different in operation or in any way hurt the system.

2) It's just a test of sensor/ECU responses to extreme rich and lean ECU inputs. It doesn't test the sensor's ability to respond to normal, rapid mixture variations.

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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).

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.[Higher for Regina]

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

"i am testing the functionality of my o2 in 91 740wgn non turbo.according to the process in the brickboard .when key is set to start position (engine off)it should read battery voltage at heater power wire(red).i don't see any voltage drop until the car is running."

• The heater voltage is applied from.by the Fuel Relay. Except for the brief pump run at Key On, the Fuel relay os only energized during cranking and running. So what you see on the heater wires is normal.

But I am interested (read confused) when you say:
"...it does the same in my 93 940 sedan.also when probing the signal wire(white) and sig return(green) the voltage fluctuate
between .01 and 1.1V..."

• In my experience here, the non-turbo '91 740 (and '93 940 like mine) would have the Regina FI system. That means a unique (non-Bosch) O2 sensor would be required. That Titania-based sensor has no green wire at all, and has the following wire (color) assignments:

Black Connection: Signal out ("return")
Red Heat + (positive)
White Heat - (negative) and Signal feed

Till now I know of only one brand of Titania O2 sensor, the NTK at Sparkplugs.com .

Could you give us more info on your O2 sensor brand/type, where purchased etc.



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

How quickly does the meter swing back and forth across the 0.45 volt point? That is the critical test that determines whether the sensor is good or bad. Minumum 8 cycles per 10 seconds. Anything less and the sensor is sluggish. An exhaust analysis would show this right up as slightly high CO with way high NOx.