Oxygen sensor and chip-tuning 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

 

[GregLocock]

No, production car open loop air fuel ratio is set by a compromise, not just MBT.

Reasons why production OL tune may be lean at a particular speed and load:

some parts of economy/emissions drive cycle may use OL map at some point.

problems with oil washdown

Reasons why it may be rich:

to reduce egt

to reduce cat temp

I'm sure there are others, it is a long time since I played with EECs, and I never did fuelling stratetgy.

At WOT, high rpm, I'd expect a production EEC to be running richer than MBT for cat cooling.

I have to say I am extremely dubious that re-chipped cars will get enormous increases in power unless physical changes are made to the engine/car, or the red line is increased.

It would of course be trivially easy to change the throttle response curve in a drive by wire car, which may give the appearance of better pickup.



Cheers

Greg Locock

 

[zimbali]

Thanks Greg,
In fact, The power for a chipped car is upto 10% more than a normal car with the same rev limit (some 7-11 hp is normal and realistic with no rev-limit change). In some cars as you said engine runs very lean due to some emission legislations. Whenever Mechanical guys cannot improve the engine Geometry with a low cost, electronics guys just limit the fuel in that region of load and rpm. You've defenitly experienced that some engines don't have a good torque in some rpms and it MIGHT get better after that, which is normally is not possible (I know some VVT stuff and Variable intake lenght do that, but I mean in a normal street car, which is supposed to have one Torque peak).

And please let me know, what you play with apart of fuel and ignition maps with an ECU? I'm interested to have any other idea about that. The throttle one was a good idae, for partial load though.

Anyway, my question is still here, how can you change the injected fuel and Oxygen sensor does NOT interrupt you to do so? Philosiphy of Lambda sensor is adjusting the A/F to 14.7, and it is annoying enough and will take the control of closed loop control, if A/F is not 14.7 +- 0.05. If I'm somewhere wrong please let me know.

Cheers

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

Cheers
Zimbali

 

[evotech]

10% is not common and very unlikely.Most of the time the improvement is around 5% or less.In most ecus it is not possible to change the target a/f ratio from 14.7/1, that is because the standard oxygen sensor is designed for precision at 14.7/1 and the ecu correction algorithms are designed with this purpose also. In the latest ecus like Bosch ME7 which usually have wide band oxygen sensors you can set any a/f ratio you want at any rpm and load.The latest cars with Bosch ME7 are not capable of more than 1-2% improvement due to the correct a/f ratio at full throttle of 12.8/1 nd the sophisticated knock control.
Regards.

 

[zimbali]

Hi evotech,

Thanks for the reply. Actually my data for power improvement is from some different chip-tuning sites. All of them quote more or less the same improvement. For example for a Peugeot 206, 1.4 Gasoline: some of them say 5-7 hp improvement the others say 6-8. This is 9-12 for a 206 2.0 GTi. It is almost 10%. I think if it was something very far from real, tehre should have been different quotes from different companies.

If you take a look at the cars they can re-chip, you'll find the list covers almost every car, new and old. For some cars they provided dyno-test results as well. You can check it at

http://www.superchips.co.uk

or

http://www.obdtuning.com.

Also, I found some people on the net, describing their happiness with their chiped car, they were personal sites. some of them described it as the same power as A/C takes from your engine.

Even if it is near 5%, I'm still interested where this power comes from. As you said Oxygen sensors don't let you have more fuel and the CPU will correct the map regarding to the signal coming from the Oxygen sensor. Advanced is not possible that much due to knock sensor.

So, what's happenning here in this big buisiness(chip tuning)? Is it all fake and wrong? Or is there a trick somewhere?

Cheers

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

Cheers
Zimbali

 

[GregLocock]

I think you need to find out whether the car in question is running open loop or closed loop at full throttle.

If it is running CL then the only options are to either bias the centrepoint away from stoich, and I have no idea if that is feasible, or to put it into open loop.

If it is open loop then the AF ratio is set in a lookup table and the O2 sensor is irrelevant.

Our cars run OL at WOT. The new Euro emissions requirement may force manufacturers to run CL at WOT.


Cheers

Greg Locock

 

[zimbali]

As far as I know, they still work in Open-loop at WOT condition. And at WOT the A/F ratio is something that gives the best performance itself, so there is no point to change it. In some other parts, Evotech says that some cars run very richer than 12.8 (like 10-11) just to be on the safe side and for the worst scenario. I don't know how it is true in new cars. If you look at the Torque- A/F graph you see that it peaks at somewhere 12.2-12.9. I think at WOT engine is already in its best condition to generate torque.

Chip-tuning companies can't change part-load condition (as engine works in Closed-Loop) and WOT seems to be already optimised . So what do they do for improvement?

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

Cheers
Zimbali

 

[GregLocock]

Please re-read my first post. It identifies some reasons why a manufacturer might not use MBT (mixture for best torque) when in open loop.

We, definitely, run richer than optimum, so, a chipper could lean out the mixture and get higher power.

We could not do this as it would overheat the cat. The chipper can, because he doesn't have to pass the same tests as we do.




Cheers

Greg Locock

 

[patprimmer]

From what I have seen, they change something else like the exhaust system or camshaft, so that the original factory settings are no longer ideal, then they correct their chip to optimise the modified motor, not the std motor.

Regards
pat

 

[zimbali]

Thanks Greg,
It helped a lot. So you mean they just change the WOT setting. It seems reasonable, logical and true to me.

There is a link at diy-efi (this is one of the dezens) shows how to remap. I don't know how expert the author is, but sounds quite experienced , here is the link:

http://www.diy-efi.org/gmecm/papers/tunetip.html

There is a part describing about part throttle tuning as well. As the result of this discussion, it is useless to do part-load fuel re-mapping. Any idea?

cheers

 

[evotech]

Hi Zimbali,
The data I have is from my own experience. I have tuned more than 400 cars on a dyno. I can tell you that most of the claims of most of the chip tuning companies are exaggerated. Especially in the newest cars there is no improvement to be made unless the engine configuration has been changed( camshafts,capacity etc).Part throttle tuning depends on the situation and the ecu you are working on. It will always be at 14.7/1 except from a racecar. You will need to change it if you have made big modifications to the engine, againg to help the ecu maintain 14.7/1 with the smallest correction possible.
Regards

 

[zimbali]

What do you think about this idea?

Feeding ECU with a voltage (I think A/F=14.7 gives some 400mv, if I'm not mistaken) that ecu thinks everything is all right. Then you can change fuel-maps and set them for best torque not least emission. ECU doesn't force any correction factor as it thinks it is 14.7.

Any suggestion?

Cheers

 

[GregLocock]

Why are you messing with the part throttle map? It won't affect the full throttle performance of your car, all you are likely to do is to ruin your cat.

Cheers

Greg Locock

 

[zimbali]

Yep you're true, but I know that Greg, just for argue and imagine that I'm living in a country that Cats are already ruined due to leaded fuel!!! (I do live there, don't ask me where ).

And for WOT, do you suggest to make the fuel map a bit leaner? Are you sure that all cars introduce more fuel in WOT and higher rpms to make the exhaust gas colder?

Won't it cause a bad effect on Volumetric Efficiency? Because when the mixture is richer than it should be, it vaporizes and makes the inlet manifold cooler that rises the Vol. Eff. If I make it a bit leaner, the inlet temperature goes a bit higher and lowers the Vol. Eff. How do you see this trade-off? Which is more important?

Thanks for any help again.

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

Cheers
Zimbali

 

[GregLocock]

No, I am not sure that all engines are rich at WOT. Ours are, at high rpm anyway.

I don't think VE will be much affected, but I've got no figures to support that.




Cheers

Greg Locock

 

[patprimmer]

Zimbali

If you know beforehand you are going to ruin your cat, why not remove it first and replace it with a pice of open pipe, then retune the ecu to optimise the fuel supply for maximum economy at part throttle and maximum power at full throttle.

That way you can at least sell the cat to recover some, if not more than all of the costs of the project.

Regards
pat

 

[zimbali]

Let me tell you the scenario:

Some car manufacturers in my country started to produce (actually assemble) some new cars. When you are not an expert and expert people are expensive and you just want to go through the production for more money, you prefer not to change anything and do it the same way the actual manufacturer does (by using the CKD parts coming from that manufacturer).
As far as I know,and for that reason, they didn't touch the ECU and its software, but they removed the cat. It's funny if I tell you they didn't remove oxygen sensor ... because ECU needs its signal to work properly, or because the main company wanted to sell its O2 sensors . Now I want to re-chip these new cars that for no reason are not running for the best performance. (Max torque and power released form the company publications are the same as the cars sold in Europe).

Any idea about the principle and practice of how to do this with all these descriptions? How to deal with O2 sensor in part load? anybody had any PRACTICAL experience?

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

Cheers
Zimbali

 

[Retracnic]

Zimbali,

I have spent the last several years trying to &quot;fool&quot; factory ECU/ECMs with both homemade gadgets and aftermarket systems. In the end, it's a near hopeless struggle.

Here's the scenario: during CL (closed loop) operation the ECU will try it's best to maintain it's target AFR, which is usually some point near stoich for a naturally aspirated engine. So the computer reads the voltage from the O2 sensor then makes corrections to reach its target AFR. It can do this by adjusting injector pulse width (and sometimes ignition advance). In any case, the ECU is only allowed to change the injector cycle buy a few milliseconds. How much correction the ECU can employ varies from vendor to vendor.

So let's throw a clamp circuit on the O2 sensor and trick the ECU into thinking that we're leaning out. So the ECU richens the mixture. It reads the O2 sensor. Still lean? It richens it some more. Soon it hits the limit of the enrichment that it can add. Guess what happens now? We have a CEL (Check Engine Light), the ECU is in limp mode, and the show is over.

So that didn't work, let's try to fool the other end. Now we install a device between the MAF/MAP sensor and the ECU to make the ECU think that we are getting more air than we really are. So once again the ECU richens things up. But now the O2 readings are all out of whack. So it leans things up again. Soon it hits the lower limit of injector tweaking and we get a CEL again.

Ok, so now we trick both the O2 sensor and the MAF/MAP sensor. The ECU is happy, and the mix is now tuned for best torque. Let's rev it to redline, shall we? Oh no! What's this? Sense the injectors have a longer duty cycle all throughout the rev range, we hit 100% duty cycle before we get to redline. So now we have to go to a larger injector. But now our idle and low rpm has gone to pot, because our ECU/Injector Driver can't lower the duty cycle enough to maintain a decent idle.

So what's the solution? There are several. 1. Accept the fact that the factory ECU is good at what it was intended to do, and not much is to be gained from fooling it. 2. Understand that most performance bolt-on parts don't make significant enough change, that ECU reprogramming is required. 3 Realized that once you've reached the limit of what the factory ECU is capable of, upgrade to an aftermarket fully programmable unit.

Good Luck
Bryan Carter

 

[zimbali]

Thanks Bryan,
It was exactly the path I pass every time I think about fooling the ECU , no result at the end! But there are lots of people out there, happy with their chip-tuned car. Some people say the the result is not that significant, some others say that it's upto 10% improvement. I'm looking for the way they change the fuel maps and ignition maps to acheive this performance on their customers' cars. Almost all of them have at least one week &quot;money back guarantee&quot; that shows you'll be happy with changes, so they are confident on what they do.
I've some software to find the maps on ECU eproms. I have the sources on the net that you can have EPROM codes on different ECUs for not a big money (20-30$). Then I can use my software to find the fuel and ignition maps in that 2-3 thousands program lines. I've done it and now I've got ignition and injection maps for a honda civic. There is an option in this software that I can see the codes in the 3-D view and I can scale it to whatever I want. I also have enough enough hardware to re-program the EPROM, So what else do I need?

I need to know HOW to change fuel and ignition maps for WOT and (part load, which needs tricking the O2 sensor or something else as well). Some friends say that make it leaner as engine works in a rich mixture in WOT and high rpm, some others say richer mixture will cool down the manifold and increse the volumetric eff. You may say, take your car and experience it with both methods to see the results, and I've gotta say I won't have a car for the next 3-4 months and I don't want to blow up a friend's car engine!

So, please let me know about any suggestion.
Thanks for any help in advance.



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

Cheers
Zimbali

 

[stevo440]

To All

Instead of clamping the voltage from the O2 sensor to the ECU why not offset it X up or down to affect the rich or lean condition. So now the ECU sees stoic as (rich) or stoic as (lean). Now the ECU is happy and so are you. Now you can deal with your cat converter problems how you see fit, remove, inject water to cool, etc. Ofcourse this only works for CL operation (part throttle, idle, and cruise).

So whudayathink?

Steve