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Unnaceptable Bosch LSU 4.9 Sensor failures

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I wonder if anyone can help - I've been using the Bosch LSU 4.9 wideband sensor with a Syvecs S6Plus since the end of last year - the guys at Syvecs set up the sensor calibration for the sensor for me - as its been completely trouble free until last week where I had my first LSU 4.9 fail on me (output went high / lean AFR - it was something like 12 months old so I wasn't really too concerned)

Then weather got much colder (UK) and I saw the first real issue with my fuelling cal - ie way too much fuel fuel correction for low ECT - and way too much preliminary fuel injection - managed to flood the engine and in the process potentially destroyed the second LSU4.9 - in actual fact initially it seemed OK but it died maybe 10 minutes of light load running later after I'd resolved the flooding condition / startup fueling calibration.

Number 3 LSU 4.9 initially looked good - got 40 minutes out of that in the morning - checked it was functioning (just a free air check) around midday and then it failed maybe one minute into my journey home (engine not even up to running temp).

Now I'm in something of a fix - having used my entire stock of new LSU 4.9s in a couple of days I'm hesitant to just throw in another and have it fail immediately - these things aren't the cheapest!

Initial ideas I have:

- Sensor isn't reaching operating temp fast enough in the colder weather (problem with the sensor cal / problem with the S6Plus LSU4.9 control itself)

- Wiring issue - using a JT Innovations supplied cable - so decent quality - but the connection to the LSU 4.9 is under the car up by the side of the gearbox - no obvious muck on it but I guess water ingress into the connector *is* possible though unlikely.

- Position of sensor - its at around 11 oclock but would be protruding very slightly into the gas flow - also it *is* further than might be optimal from the turbine housing (approx 90cm).

- Batch of duff sensors - unlikely

I'd be interested if anyone else has experienced similar or might have any further ideas what on earth could be causing this....

What fuel are you running?

Are they genuine Bosch sensors?

Any tuning changes recently?

Positioning sounds good.

What about the plastic cable enclosure? It draws reference air through there. Is that free in the air without anything blocking air through the pipe-thingy to the actual O2 sensor?

Fuel is nothing out of the ordinary - 99 RON Super-Unleaded and the sensors are the genuine Bosch items. No tuning changes recently (other than pulling a heap of fuel out of the cold start from around 10 degrees and down to remedy that previous flooding issue.

Re reference air - that was a LSU 4.2 thing (but tbh I wasn't aware it drew any air in through the plastic enclosure) - These are all LSU 4.9 sensors which rely on a "reference pumping current equivalent to the stoic reference air, but without having any physical air in the cell". In any event the entire sensor attached cable is in free air.

I've personally had reasonably good luck with the 4.9 sensors. It's interesting that you've only recently seen this sort of issue after previously getting good life from them. I'd start by confirming the electrical connections are in fact sound at both the ECU and the LSU connector. Beyond this it may be worth running the issue past Syvecs and see if they have any ideas they can contribute.

Thanks Andre - I'm doing exactly that.

ejonsey are you making any progress on this? Has Syvecs come back with an explanation for why you're going through sensors?

Digging up an old thread, I've been through a few sensors, but I seem to be having a hard time identifying if my sensor has failed this time around. Was idling at Lambda 1 but I started the car today and readings were erratic getting a reading of lambda 3 at idle. Surely the car wouldn't run at all this lean?

These sensors can fail due to moisture cracking the element. What happens is you crank the engine over while the heater is powering up the sensor, and the droplets of moisture cause the cracking. Part of it has to do with position of the sensor and another part has to do with how you have your heater powered.

For our purposes A gasoline engine won't run at lambda 3. What wideband controller do you have? Did you try replacing the sensor? Where is the sensor positioned in the exhaust.

Running E85, using a Link Thunder with the on board controller. Haven't got a chance to get another sensor yet, sensor is positioned at 2 o'clock, 1m away from the turbo. This was the first time starting the car in a few days and it's been a bit colder so I dare say there was plenty of moisture in the exhaust.

Here's a great tech article from a local NZ company that addresses the common failure modes of the Bosch LSU sensors: http://www.nzefi.com/bosch-lsu-wide-band-airfuel-ratio-lambda-sensors-fail-often-aftermarket-performance-applications/

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