why dont we see diesels with A/F gauges?

[DleclairObs]

I spent a long time doing research and writing this for my auto tech class because I my teacher couldent answer it and I have always been curious. he said that if I wrote a paper on it I could get extra credit. so here:
Wideband sensors are used to determine whether a vehicle is running lean or rich. The way it works is the exhaust works its way through a diffusion gap into the pump cell of the wideband sensor. The sensor uses that to determine how much air is in the exhaust and how much fuel the motor needs. The sensor gives off between 100 and 900 millivolts. At the perfect fuel ratio for a gas motor (14.7:1) the sensor will give off about 450mV. The optimal fuel ratio differs from fuel to fuel.
Now its not very common to see these in diesel motors even in the mild aftermarket. This is because diesel engines are more and more often getting boxed tunes or already made tunes. And it is not something that needs to be constantly monitored on a diesel motor. These sensors can also be prone to getting clogged up with the soot of a diesel motor.
So some people don't understand how a diesel motor can run without one since new gasoline motors need them to operate properly. But this is because diesels don't have a throttle body. A diesel motor accelerates by simply adding fuel. This is why diesels smoke because air and fuel are not added at the same time fuel is added and the turbo is expected to provide the needed air. This is also why diesels don't need blow off valves because the turbo (if tuned properly) will only provide as much fuel as is needed.
So why would a diesel need a wideband? they are still very useful in tuning electronically and adjusting fuel pressure(especially for 7.3 and 6.0 fuel pressure). Optimally it can help you achieve proper tuning for mileage and power.
that's it if I'm wrong tell me this is what I have gathered from other forums, videos, and talking to other people.

 

[cbrown]

Since when is 289 words considered a paper? LOLLOL
Just messing with you.

 

[sootie]

So now turbos provide fuel?

 

[Kxc]

Perhaps some research into the combustion process of a Diesel engine will shed some light on ur question. In short , a Diesel engines afr would be off the charts compared to a gasoline engine. Like you already found diesels change afr to accelerate. It would be much simpler to understand if you imagine a non turbo diesel. They used to be used all over in all types of applications. The only way to increase rpm or power is to add fuel thus making the mixture extremely rich. With proper design smoke will be minimal.

In modern engines they use a table to limit smoke as compared to manifold pressure , temperature and the MAF sensor reading. Fuel pressure has very little to do with afr in the engines you mentioned above 6.0 and 7.3 . Hope this helps !


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[DleclairObs]

So now turbos provide fuel?

that was bad punctuation on my part I meant
" This is why diesels smoke because air and fuel are not added at the same time and the turbo is expected to provide the needed air" somehow I missed that.

 

[DleclairObs]

Since when is 289 words considered a paper? LOLLOL
Just messing with you.

haha it looks a lot larger handwritten on paper

 

[DleclairObs]

Perhaps some research into the combustion process of a Diesel engine will shed some light on ur question. In short , a Diesel engines afr would be off the charts compared to a gasoline engine. Like you already found diesels change afr to accelerate. It would be much simpler to understand if you imagine a non turbo diesel. They used to be used all over in all types of applications. The only way to increase rpm or power is to add fuel thus making the mixture extremely rich. With proper design smoke will be minimal.

In modern engines they use a table to limit smoke as compared to manifold pressure , temperature and the MAF sensor reading. Fuel pressure has very little to do with afr in the engines you mentioned above 6.0 and 7.3 . Hope this helps !


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that's what I was thinking with the tables but I didn't have any info to back that up before it does make sense.
I wasn't sure about the 7.3 and 6.0 statement but that's how I was told when I was trying to figure out what fuel psi to run my 7.3 with regulated return. Thanks!

 

[sootie]

The fuel pressure for your regulated return has nothing to do with how it would affect the reading of the sensor you speak of. Low pressure fuel supply and injection pressure are entirely different.

 

[DleclairObs]

The fuel pressure for your regulated return has nothing to do with how it would affect the reading of the sensor you speak of. Low pressure fuel supply and injection pressure are entirely different.

you're right I feel really stupid I had a bad concept of heui injection I get it now so my fuel pressure is not very relevant to my injection pressure as long as it is enough to consistently supply my injectors?

 

[sootie]

Correct

 

[dmd]

Diesels dont need the 14:1 ration of gas engines. They can run very rich or very lean, just depending on the fuel added.

 

[gwunter]

My experience is that you mainly see a/f ratio gauges in diesels when someone is really trying to make it run as clean as possible. I first noticed diesel guys measuring a/f ratio when I was reading about 4bt Cummins conversions. Several guys on the 4btswaps forum run them. It is mostly for tuning purposes, although could give you a heads up on a leaky injector. I have one to install on my 4bt expedition, but it's still sitting in the box, in the basement. When buying one, you have to make sure the gauge will cover the wide range of ratio a diesel will go through, as opposed to the gasser.

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[sootie]

Diesels dont need the 14:1 ration of gas engines. They can run very rich or very lean, just depending on the fuel added.

well said. Also you dont have the same consequences running outside of the optimal range on a diesel. With a gas, you run it too rich and it puts the fire out-you run a diesel too rich and it smokes a little until the turbo spools. With a gas, you run it too lean there is a risk of detonating-you run a diesel too lean and it just doesnt make as much power.

Whoever suggested researching non turbo diesels was very wise. The amount the a/f ratio changes with a turbo is phenomenal. (throttle position, load, boost, rpm etc)

 

[bruce]

So what’s for sale?