EGT vs Wideband sensor

[ropadopa]

Hey guys, Been putting in some work on my eco diesel,  Maintenance / Mods and i thought that why is it that EGT  sensors seem to be favored in diesel applications?

Im familiar with both and understand how they work, Please share your thoughts

[745 turbogreasel]

What is a dangerous AFR for a diesel?

[ropadopa]

the run lean, It seams the like 18.0 ish  at WOT.  and 75.0 at idle  , Remember on diesels which im sure most of you more fuel more power more rich more heat.

so 10.0 would be really rich and heat up. You have to read it the opposite of how a gas engine works.

[vanbcguy]

AFRs have value on diesels but they only come in to play at full power.  The rest of the time the AFR will be so lean it will barely register. 

EGTs are reasonably cheap to test and will let you see the safe limits of your engine.  If the EGTs are safe you're all good (provided a few other key things like exhaust manifold pressure are safe too).  On a gasser 'unsafe' AFRs cause detonation - you have a fairly narrow band of safe AFRs you can work with.  Since detonation isn't a problem on diesels the AFR is less important.  If it's running at 18:1, 20:1 or 150:1 it doesn't really matter but if your EGTs are too hot you're going to start melting things.

Having an AFR gauge on a performance diesel WILL help you find your ultimate maximum power output but still only in conjunction with an EGT gauge.  Peak safe performance is going to come with an AFR at around 18:1, an exhuast manifold pressure : intake mainfold pressure ratio less than 1.2 or so and EGTs at a safe value for your valves and turbo.  An 18:1 AFR is no guarantee of safe EGT values any more than a 16:1 AFR is a guarantee of dangerous EGT values. 

[ropadopa]

I some what get it,  We use the brand Innovative wide bands on gassers with good luck and what they can do for the price is awesome and affordable,  Even has eon a wood burning stove  lol  I just feel that t use to be more economical to go with EGT but wide bands for under 150 bucks these days and i  cant help to wonder.

[libbydiesel]

There is some value to O2 sensing (about as valuable as looking in your mirror to see how much smoke you are blowing), but it is not nearly as important as EGT monitoring which actually tells you when integral internal components are getting dangerously hot.  There are a couple very good choices for complete EGT setups (gauge and probe) for considerably less than $150.  How would you know how long to idle down using a wideband?   

[ropadopa]

 I have been giving this some thought,  i have been working on more modern EFI turbo gasser set ups lately and i have to remember that my Jetta is a little more of a crude set  up.  If i think back to my carburetor days it seems to help.

I would have to agree that the EGT would be more important than the wideband , but it would be usefull to help with fine tuning and tuning of the EGT.S

 Where would be the common placement of the EGT sensor for the 1.6 motor at hand.

[vanbcguy]

The best place for the EGT probe is the closest place to the engine where the exhaust ports join together.  On a turbo engine right the best place is the exhaust manifold right before the turbo.

The further downstream you go the lower the measured temperature will be.  You want the probe as close to the exhaust ports of the head as possible while still measuring the combined temperature (unless you want one EGT probe per cylinder!)

[theman53]

I don't see much of a value of the afr gauge for a diesel. It may tell you when your air filter is needing changed or if cooler days yield more oxygen than hot ones or that you are indeed running 20:1 at a certain spot. In a tuning standpoint I don't see a need for one, where an EGT gauge is very important.

V guy stated it great for placement.