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I've previously had a 4.2 Bosch wideband that lasted ~9 months, street driving including a few trackdays.
Then went to the 4.9 sensor, which only lasted a month.
Thinking about the possible causes for the short lifespan, I cant help but think that ignition or fuel cuts are probably what caused it to fail. As I'd been doing a lot of WOT tuning right up to the limiter (rather than shift light...)
One of the main things that are mentioned as reducing sensor lifespan is thermal shock.
So thinking about this...
Lets say my engine is running up to redline, gets to 8000+rpm full throttle and the limiter cuts in (whether fuel or ignition)
It's suddenly going from EGTs of say ~5-600 degrees, then if I had (naturally aspirated) inlet temps of say 30 degrees, heated to maybe 80-100 by time it gets to the exhaust. As well as having a big load of fuel dumped directly onto it, if using an ignition cut. When excessive rich conditions also make them pack up.
Seems like a pretty major source of thermal shock? Same goes for using fuel or ignition cuts for traction control etc.
Has anyone who's using EGT sensors, seen anything which confirms this?
For now I'm going to completely avoid using any of the above, and have my limiter set somewhere above the rpm of an E-throttle ramp down.
It's not something I've seen an issue with, nor have I given it much consideration. I doubt however this would be the cause of your issue. Let me explain:
While an ignition cut will result in a cylinder's worth of unburnt fuel/air passing into the exhaust, depending on the cut percentage you'll still have several cylinders continuing to fire and hence the actual exhaust temp probably won't be influenced as much as you're expecting. The other aspect is that with the exception of 2 step launch control, the ignition cut is very brief (nobody typically sits on a limiter for extended periods of time). I've not seen the EGT affected dramatically by a limiter, however the EGT sensors typically don't respond that quick and again you'd need an extended period of cut to really see the net result.
I've also used ignition cuts in multiple cars for gear change control and haven't seen adverse sensor life from this. Aggressive ignition retard on a 2 step limiter can damage the sensor but this is from the shock waves of the fuel/air combustion rather than any unburnt fuel.
Thanks for the feedback.
My only other thoughts are that my idle strategy was too aggressive on cold start. I datalogged idle speed vs engine temp from my daily driver, and used this as the basis for idle control on the other car.
On a cold morning it would start out at 2400rpm (I'm assuming for x-tau related reasons) and then ramp down pretty quickly by the time it got to 50 degrees or so. Which is maybe good for emissions but not so good for a wideband.
However I've now amended it to start at 1200rpm instead then drop to 900 when warm.
Or, maybe I just got unlucky with a dead sensor.
Fingers crossed I have more luck this time around!
2400 rpm is a pretty high cold idle speed. I'm not sure this would relate to your sensor issue but it's certainly not necessary. A lot of late model factory cars do what could only be considered to be some strange things on cold start with the intention of building heat in the catalytic converter. I normally aim for around 1200 rpm when cold dropping off to 800-900 (provided the engine is happy idling at these sort of rpms) so what you're planning sounds sensible.
As you say, it may be a bad sensor. Good luck for your next one.