Chip-tuning and Oxygen sensor (Lambda sensor) 2

[zimbali]

Hi,

New engines usually use 6 or 7 different modes for fuel injection and spark ignition timing (Start, warm up, open loop, closed loop, hard acceleration, deceleration). There is one map in the ECU that contains the open loop data, this is the one that always all people talking about; a 3-D map. There are several 2-D tables to correct the values of the 3-D map depending on the mode which engine works in. Besides an engine is usually in its closed loop mode, i.e. Oxygen sensor(s) gives feedback to the ECU to adjust the A/F ration at 14.7. On the other hand A/F ratio is in a range of [12,12.5] for acceleration mode for Wide Open Throttle(WOT) where ECU ignores the Oxygen sensor to achieve the best performance.

Now the question is, how these electronic chip tuners manage to change the fuel map (so the amount of injected fuel)? I mean if they change the map to have say A/F ratio of 12.5 for normal loads, then anyway Oxygen sensor will adjust this map until it gets 14.7(a transition in sensor output happens in A/F=14.7), because engine is not in WOT mode and works in partial load (closed loop).

If you say that in partial load this chip-tuning stuff doesn't make any difference but it adds more fuel just in WOT and hard acceleration, There would be this problem that in WOT, engine already works in the best A/F ratio to generate the best torque and any more fuel will decrease the performance ( A/F <12 will decrease the torque output). So please let me know if you can solve my contradiction.

Thanks for any help in advance.

Cheers


If you share what you know, you'll never forget it.

Cheers
Zimbali

 

[evotech]

Usually you dont have to change the part throttle closed loop fuel maps. Most ecus up till now worked open loop at full throttle and most didnt have optimised a/f ratio for power. Very common to see a 11.5 a/f and even 10 a/f on a turbocharged stock car. The reason for this rich mixtures is reliability at worst case scenarios. So most of the time on a vehicle with small modifications you have make the a/f leaner.
Regards

 

[CDC]

Speaking from experience (I run a tuning center with chassis dyno and modify A/F ratio's and ignition/injection timing as needed on gasolina and diesel engines using a series of piggy back computers made by Dastek in South Africa) I can say that changing the mixture in the closed loop range is fighting the lambda control and it is simply not done. There is no point to it either as this range is in all but a few cars only in action up to about half power at any rpm. You can gain economy on some cars by adjusting the timing in this area though. You tune for performace outside the closed loop range, mostly from 70% throttle upwards.

If you ,for any special reason, want to change a car that runs closed loop all the time you have to change the actual output of the lambda sensor at the operating points you want to change, there are piggy back intercepter computers that can do it.

Hope this answers your question.

 

[zimbali]

thanks,
this was what I was looking for. After some investigations I came up to the same conclusion. Could you please tell me how much (percentage of max bhp) is the improvement of a remapped fuel and ignition map ECU (just for full throttle and hard acceleration), is 10% for a non-turbo car a good estimate?

Cheers

If you share what you know, you'll never forget it.

Cheers
Zimbali

 

[CDC]

It all depends on the mixture and timing the car is running at before you modify it. If the mixture is close to perfect at full throttle (My experience is that this is 13.5:1 +/- 0.2) the chance that you will be gaining anything worth mentioning is small, it would have to come from the timing being too conservative. Late model BMWs for example are perfectly tuned from the factory and any claims of the pre programmed chip makers should just be laughed at. Hyundais are a disaster, they can go all the way up to 10:1 and in such circumstances you can gain up to 12%. To gain anything it is almost essential to tune on a loading dyno and having a wideband lambda sensor, measuring in real time, if you don't it can take a loooooong time and you may have many near misses or worse in the process...

Don't forget that every a/f ratio has it's own timing. Mixtures burn slower as they get further away from 13.5:1 so when you enrich a leaner mixture or lean out a rich mixture the consequence is automatically that the combustion speeds up, same effect as an ignition advance..

Hope this helps

 

[zimbali]

Thanks very much,
There is another threat named the same in &quot;automotive general topics&quot;, some friends say that engines often run very rich at WOT, like 10 or 11 for best emission. Do you have the same experience for normal cars in the market?
I think it is worth it to take a look at the other thread I said, and then let me know what I can do with that situation described in the last posts.

Thanks for your help.
Cheers

 

[CDC]

I don't know what they mean by best emission, it is well documented that emissions get worse as you move further away from lambda 1 (14.7:1). I own a couple of chevys as only reference for american cars I tuned, and they didn't have lambda control as it was not needed in the country I bought them at the time. Yes, these were running rich and I could gain about 10% performance with them and more economy too by advancing the ignition under part load. Economy is hard to say but consider I run an Impala LT1 on cruise control at 140 km/h for a few hunred km in one trip and loaded with 4 people and luggage use 12.5 litres per 100 km. Compared to a lot of smaller engines this is not bad at all.

The best way to know if your car runs rich under WOT is to visit a dyno center, preferably with a loading dyno, and have the a/f measured at various loads. This will also tell you that your engine is up to spec and that under part load lambda control functions as intended, cooling circuit works ok under full load etc. From there you can decide if you should have it programmed or not. Stay away from pre- programmed chips as their benefit is like playing russian roulette, there are just too many variables involved and many have been programmed on cars that had bad sensors or something wrong to start with, hence the claims for 'standard' gains...

Regards

 

[andyv8]

Normally post on the engine forum, but thought I'd throw my penny in.....
Most modern cars run very rich at WOT (11-12:1) to keep the close coupled catalyst cool.
Most modern ceramic starter cats are so close to the engine for reduced warm up times, that if the engine was to run anywhere near stoichiometric at WOt, then the resultent 950°C exhaust gas temperatures would just start eroding the cat bricks and reducing the durability.
Most cat manufacturers that I've worked with say that 850°C is the max continuous running temp with only very small & infrequent excursions allowed to 900°C.
You also need to measure these temps in the cat brick, measuring gas temps will not give the full picture.

It does make me cry when I see modern cars being leaned off at WOT to increase power. The customer doesn't normally get told that he'll be lucky to get through his next emmisions test after some hard use......
(although I admit that a few manufacturers do leave a bit of leeway, but this is reducing now)

Andy

 

[zimbali]

Now fuel injection is a bit clear to me, go a bit lean to go a bit faster! (at WOT).
does anybody have any idea about Advanced angle? Is it true to say Advance more until you detect a knock? Is there any general rule?



Cheers


You can live in your car, but you can't drive your House!

 

[andyv8]

Basically yes.
Can't give any real guidelines because it depends on a lot of engine parameters such as:
compression ratio,
volumetric efficiency,
heat rejection,
fuel,
hot spots in/around the combustion chamber.

An modern 4v aluminium engine would be able to stand a lot more advance than an old iron 2v engine.

Most modern engine management systems count knock signals through the knock sensors and start to back off the ignition when a given threshold is reached. They then slowly advance the ignition again until the threshold is reached. In this way, they effectively actively calibrate the ignition every few rpm to get the maximum ignition advance. This is why putting higher octane fuel in modern cars can give a significant performance increase due to the EMS &quot;learning&quot; that it can increase the ignition advance.

Andy

 

[zimbali]

Thanks Andy,
So you mean cars (try to) adjust the advanced angle in its best possible (most possible advanced) condition. As you know NOx goes high dramatically with advancing the ignition angle (NOx emission is 2-2.5 times more in 50 advanced angle comparing to 20 degree for a normal engine; from SAE Automotive Handbook,2000 Ed.).
Is there again any emission or economy considerations that manufacturers take to account and spend some performance to gain some cleaner combustion or economy?

That's why I think there might be again some possible changes to re-map the ignition, without reaching that threshold and gain more torque, in the expense of more NOx. Do you have any idea of WOT ignition advanced and if I'm true in my argument?




Cheers


You can live in your car, but you can't drive your House!

 

[CDC]

About Cat temperatures and A/F ratio.

Well, I thought this was an engineering forum..

For information directly available on the web read

http://www.randomtechnology.com/technical.html

For other, even more authoritive, publicized info about his subject read for instance 'Gasoline Engine Management' by Robert Bosch GmbH, ISBN 0-7680-0510-8 pages 26-31 and the table on page 226 for exhaust gas temperatures and pressures, maybe contradicting earlier info about 'normal' exhaust gas temperatures.

There is always a lot more, if you're still in doubt, and I suppose the SAE Automitive Handbook Zimbali is referring to will also have something to say about the subject.

The message is clear, rich A/F mixtures kill 3 way (modern) cats. The oxydation process generates a lot of heat, the richer the mixture, the more heat. Bosch goes so far as to state that &quot;when operated under favorable conditions a catalytic converter can last for up to 100,000 km. On the other hand, engine malfunctions such as misfiring can raise the catalyst temperatures beyond 1400 degr C&quot;. To me that means a cat is a consumable with limited lifespan.

In practice you may find that a car like a typical Hyundai FX Coupe 1600, MY 2000, running at 10/11:1 under WOT and being driven quite hard regularly, with the only cat being incorporated in the manifold, shows no visible internal damage after 20.000 km of useage. To me a big surprise. I did not test the cat as I don't have the right equipment nor the time for it, so maybe the effectiveness of the coating was already significantly down.

Let's stick to the facts, time is valuable and confusing people because you have not even spent the slightest effort to learn about a subject chases away people who might have valuable input.

 

[zimbali]

CDC,

I don't have the book you said to check the grapghs and stuff. I didn't find anything about relationship of Ex. Temp. and A/F ratio in the SAE Handbook, but NOx comes down for richer mixtures that could be an indicator of less temperature (?). I heared that richer mixture cools down the total temperature because the excess fuel (that is not burnt and does not generate more heat) vaporizes and absorbs some energy for that.

Any idea about this issue is highly appretiated.



Cheers


You can live in your car, but you can't drive your House!

 

[CDC]

Zimbali,

I believe we are straying from the original question: chiptuning, which I would prefer to call re-programming of ignition and a/f ratios, in the closed loop area and beyond, how it works and what results to expect. I believe the question has been answered.

Yes, in general NOx increases with increased combustion temperatures and/or pressures. Manufacturers may respect that and program a few degrees less advance at WOT than would be best for power output. Exhaust gas temperatures also come down with getting nearer to the perfect ignition point (getting max efficiency from that operating point for continuous safe operation) for the mixture in question. If you have a pyrometer and want to see this just advance and retard your car's ignition a few degrees at idle and measure exhaust temperatures under each condition.

I don't know of any countries that already test private cars under full power for emissions and if manufacturers are still allowed to release their cars to the market with whatever A/F they feel is suitable then why worry about it?

I want to make clear that we were talking about normally aspirated (NA) cars here. Evotech already pointed out that in turbo cars mixtures can be very rich and that this is for safeguarding the engine, basically against detonation and/or too high exhaust gas temperatures. The combustion chamber in those cars at those pressures running those sparkplugs and CWT has to be cooled further by means of additional fuel which doesn't find oxygen to burn in the process. Expensive but true, there are other ways of achieving the same effect but that's another topic. Search the 'aquamist' web site and it's links for that subject as one option. Search also about the new PT cruiser turbo release and the 14.7:1 a/f mixture required under WOT and the consequences for the engine design.

For the consequences of mixture on an engine w/o changing any other parameters you need an environment where this can be tested, a good engine dyno with a lot of recorders would be ideal. I don't have any and I haven't found detailed research by engine dyno operators on the web yet, nor in public literature. It is rather explicitly described in the earlier mentioned Bosch book and if you really want to get in depth on the subject you should order it. It is thus far the best and clearest written book on the subject I have found.

There are some very interesting reports from aviation web sites though, also a perfect environment to test and record subtle changes you make to mixture and ignition. The throttle position can be fixed, it is a constant temperature up there and you are normally with a number of people who can participate in obtaining data.

One website to read would be

http://www.avweb.com/news/columns/182104-1.html#series

Other things to read up would be the GDI engine and the OCP 'Air Assist' way of direct injection, look for 'OCP DI engine' on

http://www.orbeng.com.au

to see how relatively lean mixtures can work in normal piston engines under partial load conditions.

Good reading!

 

[zimbali]

Thanks CDC for all the effort you did to make the problem clear. I realy have to get that Bosch Book. Thanx again.


Cheers


You can live in your car, but you can't drive your House!

 

[speedy100]

Zimbali Hi

As I am new here I just read Your question in the beginning.
About the clamed output from the various tuners the story is as follows. You are right about the ECU correcting the mixture in CL. BUT in chip tuning the job is done on a dyno and as You know the engine on the dyno is measured at WOT where most ECUs run OL.
In the tuning procedure about mixtures the tuner usually for NASP standard engines adds about 1-2% of mixture to the hole range above about 2500 RPM just to be in the safe side and lets the CL do the work up until WOT. The trick is that in mid range the engine runs as standard, emission and performance wise under steady speed, but because it takes some time to correct the ratio during acceleration, the driver feels a stronger acceleration and is happy... while at WOT the tuned map takes care of the fueling.
Now if You add the mod. in the Advance map, this helps with torque and adds more acceleration feeling and actual performance so there You have Your answer.
If the factory margins allow we have an average 8% gain as shown in the dyno charts at WOT.
Of course One must use 98+ gasoline or the knock sensor, if used, will do its miracle and there goes the performance gain... in most chip tuned cars.

Take care
Speedy100



You think knowledge is expensive?
Try ignorance...

 

[zimbali]

Hi Speedy100 ,

Thanx for the reply, it was a very practical one. The only issue is that some friends here say you've gotta shift the injection maps a bit lower. If you take a look at the whole topic here, they say some cars use more fuel (A/F = 10.5-11) to make the combustion and exhaust gas cooler in WOT to help the 3-way CAT working better. Best torque is achieved somewhere near 12.5, so you need to LEAN the mixture in the map if you're looking for better torque. What you said about riching the mixture a bit, sounds graet when you're not in WOT and accelerating. But if you rich the map then it will be richer than 10.5-11 in WOT and the car looses torque.

Do you have an idea about this issue?



Cheers


You can live in your car, but you can't drive your House!

 

[speedy100]

Hi Zimbali,

As You know in chip tuning, all the tuner is trying to do is to optimize the fueling and ignition for best performance trying to discover the least possible margin left over from the factory programming.
In the factories the people who do the mapping are instructed to leave margins on these parameters because the same cars go to different markets-countries where the quality and octane number of the gasoline is not the same.
This means that more than 95% of the cars that are coming out of the production lines are in some stage intentionally &quot;detuned&quot;.

Now about some cars having rich mixtures from standard.
For me there are two reasons for this. One is that intentionally they have gone out of the right way in order to cover up for a design mistake... or the people who did the programming they have hit the target of consumption and emissions and they did not have the time or the will or the knowledge to improve further towards performance... not to mention that the life of the cat is shortened very much by rich mixtures... So something is &quot;suspicious&quot; in these cases.
If something like that happens, (very rare), the tuner has to do its job and optimize the fuel again towards performance. If He has to cut down on fuel He does that in order to get the best performance possible while He stays within the pollution standards since We are talking about every day cars and not racing cars. This is very easy to do by monitoring Lambda and Ex.Temperature while on the dyno.

Best Regards

Speedy100



You think knowledge is expensive?
Try ignorance...