Benefits of a lambda sensor

[keybaud]

MY engine doesn't have a lambda sensor and is old enough not to have to meet the emissions tests; however there is a boss for the sensor on the exhaust. As I'm about to upgrade from carbs to an Omex 600 with 48mm throttle bodies, is there any benefit to fitting a lambda sensor at the same time?

 

Edited by - keybaud on 15 Jun 2012 10:10:14

[TomB]

Similarly, Im wondering whether I should get a boss welded on my 4-1 collector to allow a wide band lambda to be fitted (I dont have one) to help with mapping on my recently installed Emerald/ TB combo. Id be interested in any replies to Keybaud

[gundersen]

If you use the lambda sensor in the conventional way (only in the band between WOT and idle) my understanding is that you gain improved fuel consumption at cruising speeds.

I don't know if that is relevant to you, or how long it takes to pay back the cost of the lambda probe

 

Last time I was at the rollers I had a talk with the operator, and he said that on new ECU's they also use the lambda reading as a target at WOT. But this setup is quite different as opposed to the conventional setup used by for example Emerald.

[TomB]

WOT?

[gundersen]

Wide open throttle

[skydragon]

KB - You are going to have to get your car's ECU mapped and the Rolling Road you go to, to do this, will use their own wide-band lambda probe to measure AFR and map the car. The only benefit of fitting of you fitting a wide-band lambda probe yourself is if you want to try and do the mapping yourself (see my note below). This is not about emissions really, although that is obviously a side-result, but about getting the car mapped so you know it is running correctly.

 

TomB - I'm guessing you have a base map already in your Emerald ECU which works 'OK' and you are looking to try and improve on this? If so, I'd suggest you visit a decent Rolling Road and get it mapped there, at least you know the job is 100% ok then. As an example, I ran my Emerald ECU with a base map to get it started up, but found that this map was way out on certain throttle settings and we only really saw this when on the RR. Every car will be different.

 

I've used a wide band lambda and controller on my car and although useful for seeing AFR and injector mapping, it doesn't really replace a proper RR session where they can hold the car running stable at certain RPMs for a long time whilst altering mapping (Injector and ignition). It's nigh-on impossible to do this properly on the open road. Don't forget it's not just about AFR and injector timing but also about ignition timing...

 

It's worth noting that if your base map is way out at some rpm, you risk engine damage, such as running very rich at low rpm and having bore wash and glazed bores, or running lean and melting pistons/valves at high rpm etc.

 

If you fit a wide band lambda, it's good as a sanity check that the AFR is within sensible limits at tickover and high rpm, but IMHO it doesn't replace a RR session.

 

Hope this helps

 

Chris

 

 

 

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[charlie_pank]

A narrowband (normal bog-standard one) isn't a great deal of use except under some very specific circumstances.

 

Widebands however can be used to read the AFR. Any RR you go to will have a wideband, so you don't need one of your own if you're going to get them to map it.

 

There are 2 schools of thought though, one says, as above that you must go to an RR to get the fueling right. The other says that you can map it on the road if you have a wideband and use the Emerald's (or other ECU's) self-mapping function - with this function all you do is set the target AFR and the ECU makes the appropriate adjustments all the time to reach the AFR values.

[Myles]

I bought a wide-band many years ago as part of a bulk-buy. The Emerald of the time could read the info., but wasn't then at the point of being able to do anything other than closed-loop running to optimise fuelling in a cruise situation - it hadn't got the AFR-target functionality (and I've never had it upgraded).

 

As part of the bulk-buy, I was given FOC a live digital readout gauge which has been mounted ever-since on the corner of the scuttle. Basically, it's just another 'worry gauge' - but it's nice to glance down and build up a picture over time of the normal envelope the engine runs in.

 

I certainly don't miss this in my other 7 (the Blackbird BEC-engined Westie) - but then Mr. Honda built that one and I pretty-much take it as read that it will diligently perform day-in, day-out without the kind of worry associated with an ageing, modified k-series with dubious wiring!

[skydragon]

kind of worry associated with an ageing, modified k-series with dubious wiring!

 

Oh dear, my, my

 

Sound nearly as bad as some BB's tendency to let go on No3 piston when pushed hard 😶‍🌫️

[skydragon]

....back on topic

 

Unless you know the target AFR Vs rpm table you want (do you?) and can drive the car on a constant throttle at most of the load sites for a sensible period of time, you are never going to be able to map the engine anywhere near as well as a RR session.

 

Having a wide-band lambda also doesn't solve the issue of what ignition mapping to use, whereas a RR session will sort this out too.

[charlie_pank]

How long do you think the lambda probe needs to get a reliable reading?

 

here they reckon the lc-1 can read in 0.005s

 

At 7000 rpm, you're doing 116.66 rps

So you're doing 0.583 revolutions each 0.005s

Half a revolution is one cylinder firing (in a normal IL4)

So at 7000 rpm the lc-1 can read individual cylinders firing.

 

But it takes some time for the gas to get to the probe...

Rover 1600 cylinder has a volume of 400cc.

Each revolution has 2 cylinders blowing out gas = 800cc

At 7000 rpm it is blowing out 7000 x 800cc of gas = 5,600,000 cc of gas per min

This is is 5.6 m^3 per min or 0.0833m^3 per sec

I reckon my exhaust has a 3cm radius so the cross sectional area is .002827 m sq

At that area, 0.0833m^3 would occupy .0833/.002827 = 31 m

Therefore the gas is moving at 31m/s

 

The distance between my lambda boss and the cylinder must be about a metre so it takes .0322s to get there

 

.0322 + .005 = .0372s

At 116.66 rps that's 4.3 revolutions or 8.6 sparks between a squirt and a reading - is that too much of a delay for your ECU to map on the fly? What if it built that delay into its calculations?

 

 

When you do your fastest 0-60 run you'll go from 2500 to 7000 rpm in 5 seconds

I know it's not linear, but let's assume it is...

In 5 seconds you'll get 1000 points on your AFR / rpm graph is that insufficient? How many points would an RR map in a session and how many would they interpolate?

 

Please someone check my arithmetic, I normally make a silly mistake somewhere!

 

 

Edited by - charlie_pank on 15 Jun 2012 17:08:33

[The Pikey]

I heard that all the lambda does on our ECUs (MBE, Omex Emerald etc) is work up to about 2700 revs or so. It's only a narrow band type and is only there to get it through the IVA/ MOT. At higher revs the ecu switches the lambda control off and fuelling is then working on the map.

 

jason

[Pezky]

I have a lambda on my Zetec / Omex 600 ecu & TB's

 

It can be set in the ecu software when the lambda is used, mine uses the lambda upto 4k rpm & 50% load. Car feels sluggish but can get decent fuel range.

[Phil B]

Keybaud,

As has been previously stated the RR operator will use a wideband lambda sensor to read AFR when defining the injection and ignition maps.

The Omex 600 unit cannot read a wideband output to adjust fuelling, you need the 700 to have that level of sophistication.

However, the 600 can read a narrow band signal and can trim fuel up/down in response. This function can be set to operate up to a max rpm and throttle position (engine loads). Outside these limits it is ignored and the power map runs unchanged.

I had my Zetec on 45 Tbs and Omex set up by the 2 Steves ( ) and they activated this narrowband lambda trim function. I have to say that I very pleased with the results and it seems to me that the fuel consumption is improved when cruising or just bumbling along on light throttle, which is so easy to do with the Zetec engine.

 

Phil

[6speedmanual]

Charlie

Interesting attempt at the maths. However, that is for an engine just pumping air at 100% volumetric efficiency.

Actually the huge thing missing is the combustion of fuel which produces vast volumes of gas as the fuel chemically breaks down and changes into exhaust. A chemist can work out the numbers.

Then there's the issue of volumetric efficiency whereby there will be less than 200cc of air introduced if below 100% or if lucky and some ramcharging/pulse effect could be 100% or more.

Combine those with gas being compressible and cooling very fast as it goes down the tube.........

 

.......means that.....

 

.....quite honestly I have no idea how far out your sums are. Just reckon a long way out.

 

Any chemists and rocket science thermodynamicists in the house?

😬

 

Peter

[charlie_pank]

Yeah, I know it's not going to fill 100%, which would mean there's a smaller volume of gas, which will reduce the velocity I calculated. The fuel is going to burn and make gas which wasn't there before which will mean the gas is traveling faster down the pipe than I calculated.

 

Surely we must be in the right ball-park with my calculations - I'd be interested to learn more.

 

Even without them we can know that if 0-60 takes 5 seconds, if you were at max revs throughout then you'd have 1000 datapoints 5ms apart...

[6speedmanual]

It is possible to calculate exactly (if you are good at physical chemistry), but I believe the expsnsion from liquid petrol combusted with gaseous air results in exhaust gases in the order of 500 to 600 times the volume of the inlet mixture. This massively outguns any calc error due to volumetric efficiency.

 

Where ve is important in the valc is because if ve was only 80% (quite possible) then only 80% of the exhaust gas will be made. This could have a significant effect on the calculated vol of exhsust going down the pipe.

 

Now I'm going to watch the end of the footy with a take away curry.

 

P

[keybaud]

Quoting Phil B: 

However, the 600 can read a narrow band signal and can trim fuel up/down in response. This function can be set to operate up to a max rpm and throttle position (engine loads). Outside these limits it is ignored and the power map runs unchanged.

I had my Zetec on 45 Tbs and Omex set up by the 2 Steves ( ) and they activated this narrowband lambda trim function. I have to say that I very pleased with the results and it seems to me that the fuel consumption is improved when cruising or just bumbling along on light throttle, which is so easy to do with the Zetec engine.

Phil

 

Thanks, I'll have a chat with my local rolling road guy, to see if he thinks it's worth fitting the narrow band one for economical driving at specified revs.

[Rich N]

Very interesting discussion, but I do wonder if the ecu (emerald, in my case!) is capable of sampling AFR values anything Like as fast as you're hoping....

[charlie_pank]

Rich, if the limiting factor is how fast the ecu can react to inputs (eg. Afr, tps, rpm), we really shouldn't be worrying about whether the map was created by man or machine, we should be worrying about whether the ECU can get to the right bit of the map in time!

[gundersen]

Quoting Rich N: 

Very interesting discussion, but I do wonder if the ecu (emerald, in my case!) is capable of sampling AFR values anything Like as fast as you're hoping....

The emerald has an option to limit AFR sampling to 12 times pr. second (and slower), so it seems that in normal mode it can sample it quite fast.