Dead O2 Sensor

[anupaum]

I'm writing this from Williams Lake, which is roughly a five hour drive north of where I live. (I'm staying up here this week to meet with students I teach online.) After recalibrating my O2 sensor a couple of weeks ago, the truck wasn't running quite right and I thought I'd need to re-tune my VE tables. My intention to re-tune didn't pan out because I simply had no time to work on it. Although the truck ran well on the trip up here, for the last few days it's been struggling to idle and just doesn't seem to run like it should.

Yesterday I plugged my laptop into the Megasquirt and discovered, to my dismay, that my O2 sensor readings are fluctuating between the two extremes as I drive. I KNOW that my VE tables are tuned well enough for factory-like driveability and emissions, and the Megasquirt is properly set up for the wideband sensor, so this makes NO sense! If I give the O2 controller authority over my A/F ratio, the injector pulses and duty cycles bounce in direct proportion. If I shut off the O2 controller authority, the injector pulses and duty cycles run smoothly as I work through the gears. This makes me think that my expensive, wideband O2 sensor has gone south . . .

Does anyone here have any experience with diagnosing this kind of problem? How can I tell it's my O2 sensor and NOT my LC-1 wideband controller?

Your advice will be appreciated!

robert

 

[TireIron]

Well the first thing to do is check over all the wiring for the wideband and the LC-1 for any damage just in case it got rub frayed or melted by accident.

If that all checks out it may not be a bad idea to pull the sensor again and make sure its not all caked up or plugged up by carbon from when it was running poorly. If it is I've heard that you can clean the probe by using a propane torch a little bit on it to burn away the carbon deposits.

If it looks like its relatively clean and the wiring is all set you can try for the heck of it to do a fresh air recalibration and see if it cleans out anything.

worst case if there is an issue with the actual wideband sensor itself it is a bosch part with a bosch part number so you SHOULD be able to get one at parts store just by giving them the part number. If they have a decent return policy you could get a new sensor and test it in the truck (doing a fresh air calibration on it first) to see if it exibits the same symptoms the old one did. If not then the old O2 sensor had gone bad or gotten damaged at some point. If the new sensor has the same activity that the old one did then there may be something wrong with the LC-1 or the wiring somewhere between the sensor and the megasquirt...

 

[anupaum]

I got back from my trip today, so this is the first opportunity I've had to respond.

Well the first thing to do is check over all the wiring for the wideband and the LC-1 for any damage just in case it got rub frayed or melted by accident.

That was the first thing I checked. The wiring hangs BELOW the exhaust pipe, just like the factory installation, and everything looks ok.

If that all checks out it may not be a bad idea to pull the sensor again and make sure its not all caked up or plugged up by carbon from when it was running poorly. If it is I've heard that you can clean the probe by using a propane torch a little bit on it to burn away the carbon deposits.

I guess that all depends on what you mean by "caked up" or "plugged." There IS a bit of a crust on the sensor, but it doesn't look any worse than the factory one I replaced when first installing the LC-1.

If it looks like its relatively clean and the wiring is all set you can try for the heck of it to do a fresh air recalibration and see if it cleans out anything.

That's what I did to "solve" the hard starting issue. It made NO sense to me that simply recalibrating the O2 sensor would make a difference, given that I've got my computer set up to run on the warm-up tables when it's first fired up, AND to ignore the O2 correction below 1 500 rpm.

worst case if there is an issue with the actual wideband sensor itself it is a bosch part with a bosch part number so you SHOULD be able to get one at parts store just by giving them the part number. If they have a decent return policy you could get a new sensor and test it in the truck (doing a fresh air calibration on it first) to see if it exibits the same symptoms the old one did. If not then the old O2 sensor had gone bad or gotten damaged at some point. If the new sensor has the same activity that the old one did then there may be something wrong with the LC-1 or the wiring somewhere between the sensor and the megasquirt...

I sure HOPE there's nothing wrong with the LC-1. The sensors themselves aren't cheap, though, and it makes little sense to me that I'd have to replace the sensor after 18 months of driving. I know they're supposed to be recalibrated every 3 months in boosted applications (which is a pain!), but I would expect the sensor to last longer than that . . .

Sigh . . .

Thanks for the advice. I'll let you know what transpires . . .

robert