What's killing my O2 sensors?

[bigray327]

I'm tired of replacing front O2 sensors on my car. It's constantly running rich, lean, or both intermittently... sometimes while cruising at the same throttle. I know it's easy to say that it's a tune issue, but I don't see how that's possible. I have replaced the throttle position sensor, my wideband sensor, and have cleaned the throttle body and MAF more times than I care to think about, and nothing has ever fixed the problem except swapping out O2 sensors. It always comes back to that.

The question now is... why?

Here's the failure signature. One front always fails low or high, then it downmodes from using both sensors to just one.

 

[lito]

Using OEM or aftermarket?

Sure the harness is ok?

Is always the same side?

 

[Fullboogie]

Ray, I don't know what those pictures are from - so I can't tell if you're logging short term fuel trims. If so, how much are they deviating from 1.0? Rule of thumb is if you're consistently getting more than 10% deviation, you likely have a tune problem. I'd also check heater circuit voltage. If it's low, it could be causing sensor fouling.

MAKE SURE YOU CHECK THE SENSOR WIRES. THEY ARE PROBABLY BURNED AND HAVE BEEN CAUSING ALL YOUR PROBLEMS FOR THE LAST TWO YEARS.

 

[bigray327]

Lito, I forgot to mention that I am using only Motorcraft (i.e. expensive) sensors. The harness is OK, and it happens on both sides... no rhyme or reason.

Dave, I have logged all of those things and have not seen much of an issue. I'll take some screenshots on my fancy Android phone here in a minute.

You bring up a good point about the heater cycles. My tune has the heater wire on for longer than normal, to fight some cold start issues. Maybe that's nuking the sensors, over time.

 

[lito]

Fighting cold start issues with heater?

Haven't seen a sensor fail due to more heater use.

 

[bigray327]

Fighting cold start issues with heater?

Yeah, the car would run like dog shit after going closed loop, until the engine was fully warm, so my tuner extended the open loop period and kept the heater on longer. It worked.

 

[Swarzkopf]

I've had really good luck in other platforms running Denso O2 sensors. When other sensors would foul on me, the Densos just kept on going- the shield on them seems to help prevent fouling. I even ran them with leaded gas with success. I put a pair of Densos into my Mustang last fall as a preventative maintenance kind of thing.

You may want to give them a try- I know it's not a root cause fix, but if it works...

 

[KenB]

Ask him if the O2 heater duty cycle is raised to the max in the tune. May be killing the sensors.

 

[bigray327]

Lito wins. The O2 sensor connector on the harness side was all cracked, falling apart, and burned out. It was obviously showing symptoms long before it actually fell apart, so I guess the lesson learned is that the O2 sensors themselves are probably more robust than we give them credit for. That and hairline cracks can still let fluids in*.

I soldered a new one in ($35!!) and now it's running fine. Two years of troubleshooting complete!


* that's what she said.

 

[lito]

Where is my cookie?

Nice you found it.

 

[Fullboogie]

Told you! See post above, sucker.

 

[lito]

bigray327, please give Fullboogie the cookie, lol.

 

[bigray327]

Told you! See post above, sucker.

Ha, yeah, geee... that wasn't obvious at all. You both can have ONE Thin Mint, and I get the rest.

 

[bigray327]

I wonder if the longer heater cycle caused the burnt connector. Hmm.

 

[skwerl]

Who's got the thin mints?

 

[UNICORN]

another o2 sensors problem