Wideband Issues
Turbo Mini Forums

I've been thinking about how widebands work and how they respond when fitted on an A-Series or other 5 port engine.

My testing of both carb and fuel injection with a wideband on each LCB leg has shown that the AFRs can be vary by as mush as 3 or 4:1. For example, a carb at idle will give 14:1 on the inner cylinders and 17:1 on the outers.

So what does the wideband tell you when fitted after the LCB Y piece or after the turbo?

Widebands work by first of all looking for oxygen in the gas with an integral narrowband sensor. If the narrowband measures oxygen, it thinks that the mixture must be lean and measures the %tage of oxygen (O2) in the gas and calculates the AFR.

If the narrowband cannot see any oxygen, it decides that the mixture must be rich and measures the %tage of unburnt hydrocarbons (HCs) in the gas and calculates the AFR.

So if the inner and outer cylinders are both running rich, the wideband will give an average value - yes?

Likewise if both cylinders are running lean.

But what does it do when the outers are running lean and the inners are running rich? It can't give an average because it will sense oxygen and therefore indicate a value above stoich.

Say the outer cylinders are running at 15.7:1. It will, presumably read 15.2:1 because the percentage of oxygen in the gas will be halved by the inner cylinders.

No matter how rich the inners are running, the wideband will still read lean.

Crap or what? Have I missed something?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Hi,
I didn't realise that the wideband worked like that. If it does then I would also see a problem where different cylinders are running different mixtures. I'm really surprised it is that complicated!
Cheers,
Gavin :)

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This is the best explanation of how a wideband sensor works.



Yes, it is very complicated.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Paul i can ask this on my supra club forum if you wish, we have many guys pushing 700bananas and a couple over 1000 that practical live on the dyno and also a guy called 'Ryan' who tunes race car engine all over the world i am sure one of them will know

Edit: i have cast the line... now lets reel them in

Edited by Brett on 12th Sep, 2008.

Yes i moved to the darkside

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Reading that made me feel sick.

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Wide bands do not measure raw fuel (hydrocarbons)

They measure oxygen.

when an engine is running rich it measures the oxgen content of the CO

no lambda sensor on earth measures hydrocarbons

Hydrocarbons are a result of no combustion( no spark, no flame no burn), carbon monoxide is a result of incomplete combustion ( not enough oxygen to completely convert the hydro carbons into H2O and CO2)

The lambda sensor will sense a rich missfire as a lean condition as it sees the oxygen, not the HCs

OK, the wideband does not measure hydrocarbons directly.

But the fact remains that the sensor makes a decision about whether it is measuring a lean or rich mixture from the presence of oxygen.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

There is quite a bit of information on the functioning of a wideband O2 sensor here: .

Jean

http://www.jbperf.com/

That confirms that the Nernst cell firstly determines if the mixture is lean or rich from the presence of free oxygen.

That then instructs the pump cell to suck in (rich) or out (lean) to measure the AFR.

So with free oxygen available from the outer cylinders, the wideband will report a lean mixture even if the inner cylinders are running very rich.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Doesnt matter what engine its on.

If you mount it in a collector, it can only report an average.

If you want individual cylinder AFR's, then you have to do just tat. Mount a sensor convenient to each cylinder.

Obviously that isnt always practical though. You just assume that each cylinder on most engines will be fairly close to each other.

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But that's the point: it's not an average. It will always be skewed towards the leanest cylinder AFR or show a false lean AFR in presence of misfires.

So you can't go blindly by the numbers reported by any WBO2 sensor.

Jean

http://www.jbperf.com/

It is true that it will show the leanest cylinder during a misfire, but it is still indicating that at least one cylinder is too lean.
If no mifiring is occuring the average AFR should be reasonably accurate.
A difference in max to min AFR when the WB is reading between 0.7 and 1.2 shouldn't be that bad.
I mapped mine on average AFR (with TBI) and the plugs look all pretty similar in colour - I know thats subjective but its much better than some other 8 ports heads I've had with Webers and at least as good as the twin SU's I had before it was boosted.

When the WB indicated a misfire (either steady state or under transients) I richened it up and the misfire, or hesitation, went away.

Hi,
This is the point, as Jean says it will "read" the leanest cylinder, which is all well and good when they're all reasonably close to one another. The excess O2 in the exhaust from 1 or 2 cylinders is going to throw out the readings from the other 2.
Paul, I think you'll need to get all cylinders AFR balanced before you start measuring post turbo/collector.
Cheers,
Gavin :)

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No A good WBL will read cylinder up to about 3000rpm at which time exhaust slugs will be coming quicker than the sensor can cycle the problem here is the fleshy bit reading the gauges we aren’t capable of reading a lambda sensor at 40Ms intervals however connect an oscilloscope you will happily see the sensor go rich lean rich lean until you get + 3000rpm at which point it will start to lean closet to average of the 4 cylinders and the harder you rev the engine the closer it will get to average

Hi,
Now there's a good idea!
Either some serious data aquisition (sp) software will be needed or a lot of hard work reading the scope!
Cheers,
Gavin :)

VEMs Authorised Installer / Re-seller. K head kits now available!

WB/EGT gauges. Click here for customers write-up

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PaulH.... Very interesting point.

I make the maths 10msecs per exhaust pulse at 3000RPM but I've just read up on the Innovate site and they claim the LC-1 can achieve response times of 4-10msecs despite the limitations of the Bosch sensor because they operate the heater in a different manner to others.

Have you actually seen this in practice on a scope ???

I feel some experimenting coming on...

btw, Paul (S) they also state on their site that a misfire will definately show as extreme lean on the wideband because it reads the oxygen that didn't get used. Considering your thread of a week or so ago, this is very different from an MOT gas analyser that will show the misfire as high HC by reading the unburnt fuel.

Schrödinger's cat - so which one am I ???

I was pondering this subject because of the Blown HG thread by Andy500.

He had taken it to the rollers at Emerald. They told him that the fueling was fine, but when he took the head off it was definately running very rich on the inner cylinders.

Presumably the wideband was reading around stoich.

The fact that a wideband would not pick this up is something to be aware of.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Paul,

This is all interesting stuff - I've had this issue before with what i know was 'false' readings - but recognised that it always seemed to give readings on the 'safe' side - ie it never appeared to read ok when it was lean.

Do you reckon that those CHT sensors that folks use on the VW's will provide any info worthwhile?
eg:
http://www.germansupply.com/xcart/customer...t_install_2.tpl

You mean like these:





So far the readings I get do not seem to mean very much. They are also very slow to react on an iron head.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

is there much difference in the colour of the inner and outer plugs?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

"He had taken it to the rollers at Emerald. They told him that the fueling was fine, but when he took the head off it was definately running very rich on the inner cylinders

Presumably the wideband was reading around stoich.

The fact that a wideband would not pick this up is something to be aware of"

Hi Paul, When i looked at my plugs they are all identical in colour and have a very light brownish dusting on them like yours which indicates they are all running around stoich.

There was however as you noted quite a difference in the build up on the top of the pistons with pots 2 and 3having quite a bit more on them.

From my RR printout you can see that AFR remains between 12.5 and 14 through the rev range. It starts to lean off when held at consistantly high revs (around 6k) as the fuel pump doesnt seem to be able to deliver the capacity.

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Forgot to add that Dave used his own wideband in the y piece for all the mapping/rr work as he doesnt have that much confidence in the Innovate gear!