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zimbali (Automotive) (OP)
26 Aug 03 16:35

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.

Helpful Member!  GregLocock (Automotive)
26 Aug 03 20:15
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.


Greg Locock

zimbali (Automotive) (OP)
27 Aug 03 9:22
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.


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


evotech (Automotive)
28 Aug 03 18:27
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.
zimbali (Automotive) (OP)
28 Aug 03 21:43
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 or 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?


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


GregLocock (Automotive)
28 Aug 03 21:56
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.


Greg Locock

zimbali (Automotive) (OP)
28 Aug 03 22:05
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.


GregLocock (Automotive)
28 Aug 03 22:51
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.


Greg Locock

patprimmer (Publican)
28 Aug 03 22:53
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.


zimbali (Automotive) (OP)
28 Aug 03 23:06
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:

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?

evotech (Automotive)
29 Aug 03 5:50
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.
zimbali (Automotive) (OP)
29 Aug 03 8:03
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?

GregLocock (Automotive)
29 Aug 03 20:04
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.


Greg Locock

zimbali (Automotive) (OP)
29 Aug 03 20:45
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.


GregLocock (Automotive)
29 Aug 03 20:51
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.


Greg Locock

patprimmer (Publican)
29 Aug 03 22:31

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.


zimbali (Automotive) (OP)
30 Aug 03 11:46
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.


Retracnic (Automotive)
2 Sep 03 2:18

I have spent the last several years trying to "fool" 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 (Automotive) (OP)
2 Sep 03 8:36
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 "money back guarantee" 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.


stevo440 (Mechanical)
5 Sep 03 12:54
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?

zimbali (Automotive) (OP)
5 Sep 03 16:24
Hi Steve,
O2 sensor is simply a switch that has high output for rich mixtures (A/F < 14.7) and low output for lean ones. Transition is very fast between low and high. So, for narrow band O2 sensors, you cannot shift the output voltage of O2 sensor. It is possible for wide band sensors, thoungh. But as far as I know they cost some $800 and are not popular in production cars.
The solution I thought is feeding the ecu with a square wave with equal on and off time with a frequency like 80-100 Hz. When the pulse is high, ECU leans the mixture A BIT, and waits for the next pulse from O2 sensor. If my pulse is fast enough then ECU doesn't change the mixture that much and thinks that the mixture is somewhere very near to stoic. Then I can change the maps for Part Load.  

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


Rob45 (Automotive)
16 Sep 03 16:35
Why not fool your ECU into thinking the engine isn't warmed-up yet (e.g., by putting in a very low-temperature thermostat,  or simply by fooling with the coolant temp sensor) and then modifying the cold-start map?
Then you'll always be running open-loop,  in the region you've modified.
zimbali (Automotive) (OP)
16 Sep 03 18:58

It MIGHT be possible to do that, depending on the car and model. Most cars (as far as I've found out) use a run-time error, i.e. if the warm-up time exceeds some predefined time, ECU switches into the closed loop mode.


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

Retracnic (Automotive)
17 Sep 03 0:31
Rob45 asked:

Why not fool your ECU into thinking the engine isn't warmed-up yet (e.g., by putting in a very low-temperature thermostat,  or simply by fooling with the coolant temp sensor) and then modifying the cold-start map?

That's because many ECUs have a cold rev limitter. This rev limit is usually signifcantly lower than the vehicle's normal operational limit. Also the ECU will never close idle air control valve if it's constantly seeing the engine in a cold temperature state.

Bryan Carter
framorgal (Automotive)
1 Dec 03 14:16
Usually the transition between closed loop and open loop is made by the trottle angle or position of the acceleration pedal, around 80-85% trottle, so if you can acces to the ECU parameters, you can modify this parameter and fix it at for example 25% in order to have a good Idle.

Don't forget to adjust the fuel and ignition tables to avoid discontinuitis in the transition point.


maverickgt (Automotive)
5 Jan 05 17:52
Hi I was just wondering why you couldn't add a diode on the oxygen sensor? Germanium diodes have a forward voltage drop of around .3v. This would show a lean condition at the computer and it would add more fuel to the engine. The computer would operate as if the air/fuel ratio is 14.7 but would actually be lower. I have been working on this idea for a speed density computer, this may work for your mass airflow setup also. Or maybe the MAF sensor is what you want to add it to. Let me know what you think.
IRstuff (Aerospace)
5 Jan 05 18:45
If you already have a computer, you can do whatever you want.

A germanium diode, particularly in a hot engine environment will behave quite differently than in the lab.  There might also be temperature issues during cold startups as well as possible issues with cold temperatures during operation.


Helpful Member!  Aquaduct (Automotive)
6 Jan 05 0:45
It's been quite a while since I've been involved in this, so maybe I'm dead wrong, but I seem to recall that the systems I worked with (US Big 3 EEC-IV) weren't really concerned about O2 sensor voltages. The actual parameter that was a concern was the switching frequency, not voltage.

A 3 way cat requires constant switching between O2 rich exhaust gases to oxidize HC and CO and and O2 deprived exhaust gases to reduce NOx. Fueling is then adjusted not in response to sensor voltage, but switching frequency in order to dither about stoich. The ECU will learn fuel offsets to account for system drift, but then, when you hit the limits of it's control range, you light the MIL and go into HLOS (Hardware Limited Operating Strategy- i.e., limp home) Consequently, you can mess with sensor offsets all day long and the ECU will drive fueling until it gets the switching it wants or fails. Which would be consistent with what Retracnic reported.

Changing the way all of that works would mean changing the actual control algorithms and not just some table or curve values. I can't imagine that you'd want to touch that. It would be akin reprogramming Microsoft Word only if you screwed up the interfaces (our strategy books were 6 inches thick with interwoven background and foreground loop routines), you could blow up your engine or worse.

The best suggestion I see here would be to change the throttle tip in value so it goes open loop sooner, assuming that's a single value that you could identify and change. If you could do that, you'd automatically go to WOT OL fueling and spark which would give you best power. The cold rev limiter is probably an algorithm change that couldn't be removed easily. Don't see any other suggestions that will overcome the return to swiching frequency problem.

But then again, I'm not sure I really know what I'm talking about.
Aquaduct (Automotive)
6 Jan 05 2:21
Ooh, ooh! It's all coming back to me now (dang, I really need my sleep too so I can go to work in the morning. Curse you guys). Although I can't recall exact numbers, this is how it works directionally.

There are really only 2 operating modes when it comes to fueling, closed loop and open loop (well, technically there are 3 more while you're spinning the engine hoping it'll catch, ramping to idle speed when it does catch, and warming up. That amounts to the first 15 or 20 seconds after you turn the key). Since you need to limit processor horsepower required and generate numbers as fast as you can, you can't afford real complicated math, and this routine is elegeantly simple.

Most of the time you're running CL. You've got an O2 sensor in the exhaust switching between +0.5V and -0.5V around stoich exhaust O2. You can measure the time between up edges and down edges (I'll call them UD switch time) and between down and up edges (DU switch time). When you are actually at stoich, the switch times are the same. As you drift one way or the other, the ratio between them changes. That ratio is what you are measuring.

Now you have a main injection duration time speed/load lookup table that is filled with injection pulsewidth values will keep you at stoich based on the engine configuration. This is the table that you can actually change if you do anything mechanically to the engine.

You also have short term fuel trim value called lambda that varies in inverse proportion to the switch time ratio.

The actual injection duration for each event is simply the lookup table value plus lambda.

Then there is a long term fuel trim value that is a rolling average of lambda and can be used to adjust lambda to accomodate fuel system drift. If either lambda or the long term fuel trim exceed the control system limits, you're HLOS.

And then, at a certain throttle angle, the system kicks out into WOT OL and uses another speed/load table calibrated to generating max power. Where (or if) that kick out happens will depend on the emissions certification cycle. You want to stay closed loop during all the accelerations in the cycle. As standards get tighter or if cycles get tougher, your ability to go OL will be either curtailed or eliminated and the throttle angle threshold will be raised until you reach 100%.

So if you want to tune it from the fueling side after the fact, it's virtually impossible to get much improvement from anything other than mechanical changes and accompanying fuel table adjustments or somehow getting into OL sooner.

Now spark is another matter, but staying at stoich is by definition a fueling problem and that's what the O2 sensors are primarily doing. Once you've got the right mixture, spark is adjusted to get the most efficient burn and get the pressure peak where you want it. I have my doubts you could get much in the way of tuning spark either, but, again, I can't remember that much.

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