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LSU 4.9

injectordynamics

Hey there.

When using a Bosch LSU 4.9 does zp still represent nernst cell resistance resistance? If so is the target temp still 780C or a zp value of 300 ohms? Bosch claims an absolute maximum exhaust gas temp of 1030C which would be a zp value 90 ohms. At what point should we consider the sensor to be overheated and reporting incorrect lambda values?

Thanks

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10 comments

Date Votes
  • Martin

    How accurate does zp correlate to EGT? Could this be used as a measurement of EGT?

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  • injectordynamics

    As far as I know it is only an indication of the sensor element temperature. Not sure how closely it would match EGT.

    It is held at a minimum of 780C by the heater.

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  • Martin

    If you know the sensor element temp, and you know how much duty you have to pump into the heater element to get it to that temp, surely you can set up a table to give you a rough indication of EGT at the sensor? It would be a nice feature with anti lag setups where you want to keep an eye on EGT`s for safety reasons.

    Has anyone tried setting up a table for this?

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  • figgie

    You would be reading post turbo and do not know the heat losses from the turbo itself and the exhaust mani.

    For boost enhancement it might help in keeping the turbo from becoming a molten puddle but for EGT. That has to be as close to the head to be of any real significant value. Now with that said, you should be able to get a close approximation but that requires testing. :)

    Paul

    one thing to keep in mind. The nerct cell temp is 1030c. The number I would be more concerned with would be the hex temprature which is significantly lower.

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  • injectordynamics

    Good point.

    I guess what I'm really looking for is a guide to know when the sensor output is valid, and when it is too hot to provide accurate values. Anyone at Motec care to chime in?

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  • Martin

    Hi

    In groupN rally you are not allowed to add sensors to the engine, so an EGT would be out of the question. I think if you fit a Motec OEM board and you are capable of getting an aproximation of the EGT at the sensor, you would have the edge over the compitition. With testin you will know at what temp things start to get dangerous, although you`re not reading at the ideal place in the exhaust. With this data fed into the ECU you can either reduce the air bypass (new DBW subarus) or add a bit of fuel. I think Reducing air bypass will decrease temps dramatically.

    MoTec, will this be possible?

    Martin

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  • JamieA

    Ok, I cant really answer with the exact details for you, as we would suggest that if you use a supported sensor, connected to a motec device, it is all pre programmed to control the heater to an appropriate temperature, when it goes outside of that temp, high or lo, the sensor readings will stop, and an error state will be entered, until the sensor comes back within its range, then the readings will start again.

    As for you question in particular, although this isnt necessarily the way we would do it at MoTeC, I would sugget that you would need to keep your sensor within around 70 degrees from optimal operating temperature for the readings to be able to be considered valid, even then you would also have to use a compensation table to correct the lambda readings for its offset from normal temperature.

    As for exhaust temp measurement, you would realise that the sensor will not read exhast temp if the exhaust gasses are below the operating temp of the sensor, as the heaters will have the tip heated to keep it at temp. Above that temp, it may be a ballpark indication, but I would have thought that using a thermocouple on the dyno and during testing, and then setting the tune appropriately for the engine would be a more accurate way to do this, even if you couldnt look at the temps during the rally.

    -Jamie

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  • DavidC

    Just another note on using a lambda sensor as an EGT sensor,
    This is problematic while heater duty is related to EGT the flow rate of the exhaust gas also has bearing on the heater duty required. If you imagine your exhaust gas is 500 degrees C at idle and 500 degrees at high RPM and load an EGT sensor would always report 500c. If the lambda sensor needed to be maintained at 700 degrees in this exhaust, the heater current would have to be a lot higher at high rpm and load as the “cooling” exhaust gas is flowing past the sensor at a far higher rate, even if the EGT is the same. This is another reason why lambda sensors are not all that useful as EGT sensors

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  • Martin

    Thanks for the answers :) I now understand the difficulties and limitations.

    Another query ive got, what are the oppinions on Lambda sensors, (ntk, LSU4, LSU4.2 LSU4.9) regarding:

    Life with leaded fuel
    Life with unleaded fuel
    Reaction time
    accuracy
    handling of high EGT`s

    I have done work on a Porsche 956 twin turbo. The standard placement for the sensors are in the collectors just before the turbo. A very high pressure area and extremely high temps. I know that the sensor would read richer than it should when the EG pressure is increased and that motec provides a table to comp for that. The problem is that sensors dont last very long (is this because of the high EGT`s?). Placement of the sensor after the turbo is not really an option since from the turbo theres about 200mm till the exhaust exits. What is the ratio between EMAP and Lambda?

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  • MarkMc

    Just to answer part of this discussion. Bosch recommends that the LSUs are accurate up to 850degrees, above this the value can wander a bit and they do not guarantee the reading. Past 900 degrees you can damage the sensor.

    Someone probably just needs to put an EGT close to the lambda sensor and log the zp and see how linear it is with the EGT.

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