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How wide is factory λ on a diesel

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Hey guys,

Often I hear you talk about wideband lambda sensor, and it's necessity for a controlled tuning. I understand that lambda sensor on a petrol engine is quite narrow, from factory. How narrow is lambda on a modern day diesel?

I'm looking at my BMW 2.0d lambda map, and by looking at the numbers, I'd say it's a fair more wider than on a petrol. Map contains values of 20:1 afr easy. How wrong am I?



Your not wrong. On petrol most of the time a controller is used that can only read from 20 to 9 AFR for example. On diesel and lean burn gas engines a 20 AFR dos not work well to get a o2 reading. So read this to get some idea.

Cheers Ruud,

Let me see if I got your message, you're telling me that lambda on a diesel is optimised to measure lean conditions, and is not suited to measure richer than stoich, for an example 10:1 or thereabouts?


Better stop talking about lean and richer as it’s so confusing. A diesel dos not have sparkplugs and dos not run a ideal mixture to make things combustible. AFR or lambda is absolute so loads of o2 hi AFR numbers and a diesel can have loads of o2 left after combustion on lo load for example when EGR is not active so most ECU will read these o2 numbers. Get it?

Thanks for your input Ruud. "one man's trash, other man's treasure", meaning, what's confusing to you may not be to me, and what's not to you, may well be confusing to me. I just don't get your lingo. :)

I'd appreciate if someone from HPA could answer my first post, please. :)


Usually a diesel can use the same Lambda sensor (such as a Bosch LSU 4.9) as a gasoline engine can as a Diesel will not typically go as rich as a gasoline engine (unless you are rolling coal) but will go much leaner.

Like the others have hinted, the times where I find it important to know lambda would be when it's between 1.0 and 1.25. Usually if lambda is above 1.25 the system is pretty happy and there's little risk of excessive soot, EGT, or even DPF issues. When you start to head towards 1.15 the You start to find your system limitations. Lower than that is reserved for competition use only. I've never found the need to measure lambda lower than 1.0 on a diesel. Does this help?

Cheers for pitching in Nick.

I understand the concept of lambda measurements on a diesel, that had been clear all along. What I was rather trying to find out, for academic purposes, if it's common for a factory diesel engine to come with a sensor of a wider sensing capability. I'll just look up through some manufacturers catalogue, that should clear things for me.

Thank you All for participating

None of the factory diesels I've ever tuned have come with an oxygen sensor. If you find one let us know.

Nobody likes the wiseguy, and today I get to be that guy.

My car has a λ sensor and they're pretty common in Europe. I don't know if you're blessed, or cursed, by not having Munich manufactured cars, with diesel engines, over in the USA :)

Rikko, all the VAG, BMW and Mercedes diesel vehicles I have been involved in modifying and tuning have run standard LSU 4.2, 4.9 and ADV sensors with their specific connectors on the end. So identical to a petrol car.

The only unique item you will find in the exhaust system on a diesel vehicle is a Nox sensor and controller unit (usually continental)

I have attached a screenshot of some logging from a LSU 4.9 on a diesel project running on a Motec GPR diesel project.

Attached Files

Cheers Nathan, this helps.

*thumbs up*

Thanks Nathan and Rikko for the education. I think I'd prefer a factory sensor, save me the trouble of installing one :)