how to temporarily run lean

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#21

10-10-2018, 03:36 AM

warrjon

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Quote:

Originally Posted by J_C_R

Glad to hear that answer warjon since it saves me a lot of money! I don't plan on any tuning so I'll just go with a 3 wire replacement.

My Fluke has the min/max feature, so I'll try that when a get new O2 sensors.

By the way, what performance change should I notice since I have at least one O2 sensor that doesn't work at all? Does the ECU fall back on the other sensor if one fails?

Thanks,
John

Bad O2 sensors will zero effect on outright performance because as soon as you mash the throttle the ECU goes into open loop and ignores the O2 sensors. They will effect fuel consumption on light throttle cruising.

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#22

10-10-2018, 03:45 AM

warrjon

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Quote:

Originally Posted by Fla Steve

warrjon can you tell me how to test the 02 sensors? I believe they are the original sensors; the car has 70K miles (MY 1990, V12). I'm still sorting things out, but am disappointed in my MPG. Wouldn't inoperative sensors effect gas mileage poorly?

Yes bad O2 sensors can effect fuel consumption.

Best way to test them is with a scope insitu, The waveform should oscillate from about 100 to 900mV (0.1-0.9 volts). Next best way is with a multimeter on DC and a min/max function, set max and measure the sensor with engine running the meter should peak hold around 800-900mV. Then switch to min and meter should read about 100mV.

Failing both of these you could measure the sensor with a multimeter on AC volts it should read about 500-600mV AC. Bear in mind this is not a fool proof method as you are only measuring the RMS value of the AC signal and if the engine is running rich the AC voltage will be higher and lower if its running lean. But it does you an idea that the sensor is reading and not completely dead.

Remember to ensure the engine is completely warmed up before testing O2 senors

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#23

10-10-2018, 04:30 PM

J_C_R

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I replaced the bad O2 sensor with a new one today, performed EZrider's test, and got the expected results (voltage dropped as I moved the sensor further out of the exhaust stream).

Tomorrow I'll put it on a 'scope and see what it looks like.

warrjon, concerning your comment about that such a device may not be all that useful giving how fast the voltage fluctuates. I can alter the code to have the program average over any set period, so I don't think that will be a problem. As I said, I just want some indication when I have my foot into it that I can see it's running lean.

Thanks for all the comments! I'll post again when the device is actually in the vehicle.

John

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#24

10-11-2018, 10:42 AM

Fla Steve

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Warrjon: so in order to measure anything I need some sort of adapter to give me pigtails to take readings?...Correct?
Or should I back-pin test at the ECU? Please make suggestions. Oh and which of the 3 wires am I taking readings from?
Do you have some sort of schematic/test set-up diagram? I know I'm asking a lot.

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