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2005 D3 4.4 v8 Pre Cat O2 Sensor Voltage Readings


v8Dougie
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Hi all,

Hoping someone can help. I have just bought a D3 4.4 v8 and runs well except for a lumpy idle. I have used my generic OBD2 scanner to check live data, and can see voltage for the post cat sensors, but not for the pre cat ones. The post cat sensors are reading 0.8v continually so it would lead me to believe that the engine is running rich. I cannot see the voltage for the pre cat ones, but I can see their amp draw. Is this correct, am I missing something?

Any help much appreciated.

Phil

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Yep, the sensors on this engine are 4 wire AFR sensors - NOT just 4 wire Zirconia or Titania sensors.You cannot read their output via a multimeter on volts as you would a conventional sensor.

I have only once had an emission fault on this type of engine and found it difficult to get any info on the sensors and how to check or monitor them. Even the tech chaps I met at a trade show could not answer my questions straight away as it was all a bit new then.That car was fixed by a software upgrade because it was just looking for outputs from the downstream sensors too quickly before the cats could get up to temp on short journeys.This was after I had bought a Chauvin Arnoux low amp clamp to run on my Picoscope etc...

For the life of me I can't remember any detail of what to look for in terms of sensor output. Can you see changes in short term fuel trims,and if you can are they much different bank to bank ? From memory I think you will gain more info from fuel trims than from the upstream sensor outputs. Are there any missfire codes ?

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Hi Phil,

Have you been to Disco3.co.uk? This forum is great for everything LR but Disco3 is a single focus as the name suggests.

Some fixes are scarery expensive, some are cheap. I'm not sure about lumpy idle but varing idle can be just a clean of the throttle body so it is worth a look. If you go to the forum and try to search it will requst a login, however if you search on google for the problem including the word Disco3 it will get you to the threads.

Glad to see another real engined Disco3.

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Yep, the sensors on this engine are 4 wire AFR sensors - NOT just 4 wire Zirconia or Titania sensors.You cannot read their output via a multimeter on volts as you would a conventional sensor...

...For the life of me I can't remember any detail of what to look for in terms of sensor output. Can you see changes in short term fuel trims,and if you can are they much different bank to bank ? From memory I think you will gain more info from fuel trims than from the upstream sensor outputs. Are there any missfire codes ?

Ally V8 - thanks!!! That is the information I have been after! After a quick Google, the info on this link explains it all very well indeed - https://en.m.wikipedia.org/wiki/AFR_sensor putting my scanner back on the car, I can clearly see that the upstream sensors are shown under EQ_RAT and should have a value of 1. I will do a test drive when possible and see what is going on. Also need to look at BARO readings as well.

Hi Phil,

Have you been to Disco3.co.uk? This forum is great for everything LR but Disco3 is a single focus as the name suggests.

Some fixes are scarery expensive, some are cheap. I'm not sure about lumpy idle but varing idle can be just a clean of the throttle body so it is worth a look. If you go to the forum and try to search it will requst a login, however if you search on google for the problem including the word Disco3 it will get you to the threads.

Glad to see another real engined Disco3.

Hi missingsid, yes have been on Disco3.co.uk, the have not been able to give me the seemingly simple information which Ally V8 did above.

I am holding out hope it might be a combination of a faulty O2 sensor and an air leak downstream of the MAF, but will be getting my compression testing kit ready nonetheless!

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