Help: O2 sensor resistance reading
04-02-2017, 06:35 PM
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Help: O2 sensor resistance reading
Hey All,
I will start this by being very upfront: I have no idea what I'm doing with a multimeter. At all.
I have been getting very bad gas mileage and am thinking it might be my O2 sensor that the guy I bought this truck from had replaced (pretty much everything else seems in order, this is my last guess). I have the '93 FSM and it says I should get 5.1-6.2 ohms resistance at 68º F (it's probably 60º now). My multimeter has three positions for resistance: 10x, 100, 1Kx. At 10x it read exactly .5, on 100 and 1K it was 0. Does that check out fine? Pictures attached.
Also attached are pictures of the O2 sensor (curious if anyone can identify it as original or not), as well as the plug at the end of the wire. The number 1 and 2 wires have some slightly melted plastic around the despite being nowhere near the exhaust pipe, which makes me suspicious that it's no good. Opinions? I'll try to get to a voltage reading tomorrow.
Thanks!
I will start this by being very upfront: I have no idea what I'm doing with a multimeter. At all.
I have been getting very bad gas mileage and am thinking it might be my O2 sensor that the guy I bought this truck from had replaced (pretty much everything else seems in order, this is my last guess). I have the '93 FSM and it says I should get 5.1-6.2 ohms resistance at 68º F (it's probably 60º now). My multimeter has three positions for resistance: 10x, 100, 1Kx. At 10x it read exactly .5, on 100 and 1K it was 0. Does that check out fine? Pictures attached.
Also attached are pictures of the O2 sensor (curious if anyone can identify it as original or not), as well as the plug at the end of the wire. The number 1 and 2 wires have some slightly melted plastic around the despite being nowhere near the exhaust pipe, which makes me suspicious that it's no good. Opinions? I'll try to get to a voltage reading tomorrow.
Thanks!
Last edited by adamk; 04-02-2017 at 06:36 PM.
04-02-2017, 07:47 PM
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What you are testing is only the heater circuit, and ...
Wait, it's my phone. "Hello? Antiques Road Show? Yeah, he's got a genuine GE 2527. It's worth HOW much? Whoo-Hoo! I'll have to tell him."
Uh, bad news. It isn't worth anything. Get yourself a "real" multimeter. http://www.harborfreight.com/7-funct...ter-90899.html
Okay, that was harsh. Your swinging-needle meter seems to be giving the right answer. 10x 0.5 is 5 ohms. On the 100x scale 0.5 is 50 ohms, so the actual value of something near 5 ohms would be 1/2 of the tiny division away from the zero. You can't read that. This would all be a lot easier with a $6 21st Century meter.
But all you are measuring is the heater coil (which you care about if it runs roughly for a long time on very cold mornings). Instead, keep reading in the FSM to the part about measuring the voltage on VF1 with TE1 and E1 shorted. That voltage is the "conditioned" O2 sensor voltage, so it swings from 0 to 5 volts (the O2 sensor itself swings from about 0.3 to 0.9 volts; hard to measure with lots of multimeters). In fact, looking for the voltage "swing" is easier with your swinging-needle meter, so go ahead and use it.
Wait, it's my phone. "Hello? Antiques Road Show? Yeah, he's got a genuine GE 2527. It's worth HOW much? Whoo-Hoo! I'll have to tell him."
Uh, bad news. It isn't worth anything. Get yourself a "real" multimeter. http://www.harborfreight.com/7-funct...ter-90899.html
Okay, that was harsh. Your swinging-needle meter seems to be giving the right answer. 10x 0.5 is 5 ohms. On the 100x scale 0.5 is 50 ohms, so the actual value of something near 5 ohms would be 1/2 of the tiny division away from the zero. You can't read that. This would all be a lot easier with a $6 21st Century meter.
But all you are measuring is the heater coil (which you care about if it runs roughly for a long time on very cold mornings). Instead, keep reading in the FSM to the part about measuring the voltage on VF1 with TE1 and E1 shorted. That voltage is the "conditioned" O2 sensor voltage, so it swings from 0 to 5 volts (the O2 sensor itself swings from about 0.3 to 0.9 volts; hard to measure with lots of multimeters). In fact, looking for the voltage "swing" is easier with your swinging-needle meter, so go ahead and use it.
04-03-2017, 06:06 AM
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Yeah I knew that meter was a piece of junk, but it was the only option on hand at the time and I rarely need one, so it's still hanging around.
Good to know the heater circuit is working. I guess I shouldn't be concerned about the slightly melted plastic around those wires? Just seems like, you know, a fire hazard if it's getting that hot.
So if I set Ye Olde "Needle-Based" Multimetere on the DCV 10 position I should look for a max reading of 5v on the lower row of black numbers going from 0-10? And then of course count the number of fluctuations per the FSM.
Good to know the heater circuit is working. I guess I shouldn't be concerned about the slightly melted plastic around those wires? Just seems like, you know, a fire hazard if it's getting that hot.
So if I set Ye Olde "Needle-Based" Multimetere on the DCV 10 position I should look for a max reading of 5v on the lower row of black numbers going from 0-10? And then of course count the number of fluctuations per the FSM.
