O2 Sensor Questions (1 Viewer)
- Thread starter Eicca
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IIRC they are extremely inexpensive. Like a few bucks or something. Cdan could give you an exact quote.
They usually throw an CEL code when they go bad.
People don't usually see a big difference after changing them.
They usually throw an CEL code when they go bad.
People don't usually see a big difference after changing them.
What just happened? Did I miss a joke?
O2 sensors wear out slowly, and can degrade performance and MPG long before they throw a CEL. On a former F150 I gained 3 MPG just by replacing O2 sensors at 80k. They are not cheap, through CDan they were around $150 each for my FJ80, with two required.
O2 sensors wear out slowly, and can degrade performance and MPG long before they throw a CEL. On a former F150 I gained 3 MPG just by replacing O2 sensors at 80k. They are not cheap, through CDan they were around $150 each for my FJ80, with two required.
Hmm, I guess I was thinking of something else that was cheap. List price shows $175.16 per O2 sensor, ouch.
That being said, I have seen several reports of people changing O2 sensors and seeing no difference. I have seen several reports of people changing O2 sensors and seeing an MPG increase....but to have that increase go away relatively quickly.
There's a little diagnostic box under the hood. Open that box, you should see several terminals. The two largest terminals come from the O2 sensors.
With the engine running at operating temp, take your voltmeter, place the red lead on an O2 terminal and the black lead on a known good ground. You should see anywhere between .3 to .8 volts. It will vary.
Are you high or something?
scottm
SILVER Star
A laptop-based OBDII scanner is nice for analyzing O2 sensors, I posted some screenshots in these threads:
https://forum.ih8mud.com/80-series-te...look-like.html
https://forum.ih8mud.com/80-series-te...ncrease-3.html
https://forum.ih8mud.com/80-series-te...rs-better.html
https://forum.ih8mud.com/80-series-te...look-like.html
https://forum.ih8mud.com/80-series-te...ncrease-3.html
https://forum.ih8mud.com/80-series-te...rs-better.html
- Thread starter
- #9
Yeah I'm pretty sure my O2 sensors are my gas mileage issue. Hear that when they start to go the ECU starts using way too much gasoline. Evidence certainly points to this; my truck runs totally awesome.
As a newbie, I'm still getting up to speed on the various foibles of the 80. I first came across the O2 issue in the "19.5 mpg" thread:
https://forum.ih8mud.com/80-series-tech/302452-solid-19-5-mpg-am-i-doing-something-wrong-3.html
Personally, I have no expectation of my gas engine 80 getting 19.5 mpg. If it was a diesel, yeah, but that's an entirely different set of facts. As I commented in that thread, my first full tank of around town, short trips was 10.3 mpg. As part of catching up with PO-deferred maintenance, I had the plugs and wires replaced and am hoping that helps some.
Reading that the O2 sensors may not generate codes until long after they cause reduced mileage raises the issue of exactly how does one determine when they should be replaced? At $175 a piece, does the FSM provide a clearcut procedure for checking if this is an issue with my '97?
Will the OBDII/Scangauge II that can be applied on the '97 vintage 80 yield a good indication of a failing O2 sensor or is the issue of no codes for a mileage-sucking O2 sensor a problem for all years and engine models of 80s?
I presume that the check engine light will come on for a complete O2 failure, but will not indicate the mileage-losing partial failure one might want to fix before that occurs.
Perhaps it's best to consider these O2 sensors to be a mileage replacement item, rather than a replace on failure item? With fuel prices creeping back up, inquiring minds want to know more.
https://forum.ih8mud.com/80-series-tech/302452-solid-19-5-mpg-am-i-doing-something-wrong-3.html
Personally, I have no expectation of my gas engine 80 getting 19.5 mpg. If it was a diesel, yeah, but that's an entirely different set of facts. As I commented in that thread, my first full tank of around town, short trips was 10.3 mpg. As part of catching up with PO-deferred maintenance, I had the plugs and wires replaced and am hoping that helps some.
Reading that the O2 sensors may not generate codes until long after they cause reduced mileage raises the issue of exactly how does one determine when they should be replaced? At $175 a piece, does the FSM provide a clearcut procedure for checking if this is an issue with my '97?
Will the OBDII/Scangauge II that can be applied on the '97 vintage 80 yield a good indication of a failing O2 sensor or is the issue of no codes for a mileage-sucking O2 sensor a problem for all years and engine models of 80s?
I presume that the check engine light will come on for a complete O2 failure, but will not indicate the mileage-losing partial failure one might want to fix before that occurs.
Perhaps it's best to consider these O2 sensors to be a mileage replacement item, rather than a replace on failure item? With fuel prices creeping back up, inquiring minds want to know more.
- Thread starter
- #11
I've heard that it's a good idea to replace them every 60k miles. And yes, they can cause mileage issues long before they throw a CEL.
In the factory service manual there should be a section or two explaining diagnosis of O2 sensors and where to connect a voltage meter. At idle, the voltage should be reading somewhere above .45v. If the voltage is below .45v, either there's way too much oxygen in your exhaust or the sensors are failing. The more oxygen, the less voltage. The ECU uses the voltages to coordinate with the EFI and regulate the air/fuel mixture. When the voltages are low due to sensor failure, it always thinks the mixture is too lean and thus uses too much fuel.
In the factory service manual there should be a section or two explaining diagnosis of O2 sensors and where to connect a voltage meter. At idle, the voltage should be reading somewhere above .45v. If the voltage is below .45v, either there's way too much oxygen in your exhaust or the sensors are failing. The more oxygen, the less voltage. The ECU uses the voltages to coordinate with the EFI and regulate the air/fuel mixture. When the voltages are low due to sensor failure, it always thinks the mixture is too lean and thus uses too much fuel.
I replaced my muffler and soon after got a CEL code of P0130. Why would replacing the muffler cause the O2 sensor failure and will it happen again if I replace the sensor? Is there another root cause I need to be looking at?
Thanks Dennis
Thanks Dennis
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I just wrapped up the front axle rebuild on my '94 and the motor is now running rough and the check engine moniker is coming and going. I've been tolerating a lower than normal idle for this truck, 600 rpm versus 700 (air off) and its just low enough to run rougher than normal. I realize the roughness may or may not be tied to the idle speed. Here's my question - if you guys are indicating that O2 replacement should happen every 60K, I've had them changed once in 245K miles, is it a foolhardy move to just go ahead and change them since I know I've gotten my money out of them? I haven't yet searched (this is my first thread on the topic) for how to check them and how to read the codes, and thought you guys might be able to point me to a hread like you did on the inner front axle seal. That single thread I was pointed to allowed me to go from a leaking seal and being broken down to fully repaired (did it myself). I am
hoping to find a similar thread(s) on the low idle/check engine light issue. Any advice?
hoping to find a similar thread(s) on the low idle/check engine light issue. Any advice?- Thread starter
- #14
My first guess would be that you jiggled the pipe enough while replacing the muffler you killed one or both of the sensors. The dang things are really sensitive to kinetic damage. My second guess would be that, out of freak coincidence, they chose that moment to die completely.
Replace them. Can't possibly go wrong. Do a search on testing them, I've heard it's not too hard, but I'm trying to find that out myself.
I cracked my FSM open while my 
was in the post office today to see what was involved in testing the O2 sensors. Mind you, this info specifically applies to the '97, but is so simple I suspect it likely applies to other model years. Maybe someone else can confirm this?
You unplug the lead coming from the sensor from the harness. It appears that there are four terminals on the sensor lead. You want to place an ohmmeter across the +B and HT terminals of that plug. You should get a reading of between 11 and 16 ohms at 68 degrees fahrenheit. If not as specified, R&R.
It's that simple, except that a new sensor is ~$175 per CDan, so be sure and test first. I do know from reading around that the sensors vary over the different model runs, most likely between the FJ80 and FZJ80 models at the least.
In another thread, folks have mentioned chasing the threads and using lots of PBlaster to ensure easy R&R. YMMV, depending on mileage and how much salt on the roads your 80 has traveled.
was in the post office today to see what was involved in testing the O2 sensors. Mind you, this info specifically applies to the '97, but is so simple I suspect it likely applies to other model years. Maybe someone else can confirm this?You unplug the lead coming from the sensor from the harness. It appears that there are four terminals on the sensor lead. You want to place an ohmmeter across the +B and HT terminals of that plug. You should get a reading of between 11 and 16 ohms at 68 degrees fahrenheit. If not as specified, R&R.
It's that simple, except that a new sensor is ~$175 per CDan, so be sure and test first. I do know from reading around that the sensors vary over the different model runs, most likely between the FJ80 and FZJ80 models at the least.
In another thread, folks have mentioned chasing the threads and using lots of PBlaster to ensure easy R&R. YMMV, depending on mileage and how much salt on the roads your 80 has traveled.
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Look in the front of the manual under maintenance and you will also find a running test for them. I am about to do that very test in the morning. If you need me to look it up, let me know.
- Thread starter
- #17
Got mine tested. They are indeed dead. I've heard that testing for ohms can damage the sensors so checking the voltage while they're running is the best bet. They should fluctuate between .3 and .8 volts while the engine is at 2500rpm. Mine only put out .2 at the most. Definitely dead.
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Your testing specs for the '92 feedback voltage must differ from the '94. The '94 FSR calls for a 2500 rpm hold and to test the VF1/VF2 and E1 and any feedback over 0 volts calls for the O2's to be replaced. Funny, mine both passed the ohms test within spec, but the feedback is hovering between 1.08 and 1.12 volts +/- .20 volts. Are you using an FSM for your testing?
I got the CEL earlier this year, turns out it was from a failed 02 sensor. My 95 has 2 of them so I replaced both, took care of the light and the rough idle. No diff in MPG though.
The only thing that makes this job a PITA is the nuts were so corroded that they looked more like a cone. Lots of pb blaster and cursing took place that day (spray a couple days ahead and it'll help). Make sure you anti seize the nuts going on. You may never need to replace but will make for an easier job for the next guy.
The only thing that makes this job a PITA is the nuts were so corroded that they looked more like a cone. Lots of pb blaster and cursing took place that day (spray a couple days ahead and it'll help). Make sure you anti seize the nuts going on. You may never need to replace but will make for an easier job for the next guy.
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Are you using nan FSM to conduct your testing by or did you take it to someone to test them for you?
