Basic Engine Tuning 101
#47
Nordschleife Master
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Some of your questions are difficult to answer, for example, the acceleration enrichment is complex. The first time you snap open the throttle, you get the enrichment over shoot (oly at lower Temp 2 with stock maps) , if you repeat quickly on the throttle next time a bit less and then again there's no further overshoot. Wait a little while and you get it again. The code is pretty difficult to work out. We've done what we can, brought out parameters which could be useful to have access to and adjust.
I think I understand what the LH designers were after. It's approximating the "tau," fuel stuck on the port walls. Your description is certainly consistent with that.
Here's hopefully a simple question that I haven't however been able to figure out: What changes if I change the "Base setting" on the fuel parameters screen.
When I first started messing with these parameters, I found it useful to set them to something very large or very small, then observe the effects. For example, when fully warmed up, setting the 72deg acceleration enrichment +100, when I would try to start going from a stop, the car died immediately. Basically the LH was dumping a huge amount of fuel when the throttle was opened and killed the engine. I suggest you play around with the settings to see what works best for you configuration, just be careful (i.e. don't be boosting when doing this or something like that).
For example, tonight I'll be experimenting with the "acceleration enrichment map." However, for this to be really useful, I need to know how the parameters on the fuel parameters page relate to the use of the map. In particular, what is the "Base setting?" Once I know that, I know where to look for the changes.
#48
Rennlist Member
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The Base setting is as it says - where Porsche mapped the acceleration enrichment. Incrementing base setting + or - moves the four settings up or down together. Alternatively you can edit the settings individually.
#49
Nordschleife Master
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I still don't understand exactly what the "base setting" does, whether it's additive or multiplicative and how does it use the WOT enrichment maps, but I decided to just flip the coin and try it. I increased the "base setting" to +3 and moved the WOT enrichment map around 2000 rpm to +7.
Now, when I floor it from min load at 2000 rpm on fifth gear, no hesitation.
After I was happy with the behavior, I did a back to back test comparing it to a newer car. My '06 997 hesitates / stumbles more when I floor it suddenly on top gear at 2000-2200 rpm than the 928 with these new settings. Above 2200 rpm, they behave the same.
I guess it was the "tau."
Now, when I floor it from min load at 2000 rpm on fifth gear, no hesitation.
After I was happy with the behavior, I did a back to back test comparing it to a newer car. My '06 997 hesitates / stumbles more when I floor it suddenly on top gear at 2000-2200 rpm than the 928 with these new settings. Above 2200 rpm, they behave the same.
I guess it was the "tau."
Last edited by ptuomov; 08-19-2010 at 11:22 PM.
#50
Nordschleife Master
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First, please describe the concept of load and/or MAF voltage, absolute or whatever it is. To me load sounds like work as in no load would be revving in neutral, light load going down hill, heavy load going up hill full throttle. However, as I understand MAF, it’s the measure of air entering the engine… is that the same as load (or lineally proportional)?
Voltage SuperMAF kg/h Regular MAF kg/h SuperMAF %
2.20 13.17 13.74 1.02
2.50 15.04 15.00 2.05
2.81 38.90 30.00 3.32
3.18 97.28 60.00 5.26
3.62 226.13 120.01 8.32
4.30 576.15 280.01 15.24
4.90 1043.73 480.02 24.53
5.40 1459.12 720.05 35.80
5.72 1748.60 930.06 45.62
6.00 1999.86 1051.58 55.72
6.13 2130.79 1126.22 61.31
6.33 2343.26 1239.34 70.70
6.55 2595.58 1363.77 82.33
6.78 2897.96 1500.74 96.91
7.03 3263.95 1651.61 115.44
7.30 3711.66 1817.46 139.34
7.59 4265.64 2000.00 170.64
MAF [%] is a non-linear function of the MAF sensor voltage. MAF [%] is ballpark proportional to the air flow per unit of time. The MAF signal in ST2 logs is approximately equal to a constant times MAF [%] divided rpm. Thus, MAF signal is ballpark proportional to air flow per engine revolution. Thus, it makes sense to use it as the "load" variable in the maps.
#51
Nordschleife Master
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Here's a question:
Why would one cut off fueling at deceleration, a Sharktuner option? Is it emissions / cats or fuel consumption? Or does it somehow screw with the infamous "adaptation"?
I've been testing both with the fuel cut enabled and disabled. This hs been in no-cat mode. My experience is that the car transitions much better from low load to high load after deceleration if the fuel is NOT cut off during deceleration. So far, I haven't seen any negative effects from not cutting fuel off during deceleration.
Anybody with other kinds of experiences?
Why would one cut off fueling at deceleration, a Sharktuner option? Is it emissions / cats or fuel consumption? Or does it somehow screw with the infamous "adaptation"?
I've been testing both with the fuel cut enabled and disabled. This hs been in no-cat mode. My experience is that the car transitions much better from low load to high load after deceleration if the fuel is NOT cut off during deceleration. So far, I haven't seen any negative effects from not cutting fuel off during deceleration.
Anybody with other kinds of experiences?
#52
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The fuel cut-off on deceleration is present on stock LH systems, and helps both mileage and emissions. It can boost the mileage on a stock car by 10%.
#53
Drifting
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For those that can not visualize how it works
http://www.animatedengines.com/otto.shtml
![](https://upload.wikimedia.org/wikipedia/commons/d/dc/4StrokeEngine_Ortho_3D_Small.gif)
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My question is how do I adjust the Timing and fuel mapping on a 89
Dist caps are solid...... and do you use a laptop and software to change AFR
http://www.animatedengines.com/otto.shtml
![](https://upload.wikimedia.org/wikipedia/commons/d/dc/4StrokeEngine_Ortho_3D_Small.gif)
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My question is how do I adjust the Timing and fuel mapping on a 89
Dist caps are solid...... and do you use a laptop and software to change AFR
#54
Rennlist Member
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If you find a hesitation when getting back on the throttle, then check your idle switch-- it should barely trip with the throttle closed, then open as soon as the throttle is opened slightly.
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#55
Rennlist Member
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#56
Rennlist Member
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Its essential for racing. I use a switch to disable it after start up. very high rpm and off throttle can kill the car with the off throttle cut off switch working . disabling it, allows for a smooth coast down of engine rpm.
What Wally said-- fuel cutoff on overrun is standard for the LH. The Sharktuner allows you do disable that, if you prefer. I find that it adds a nice mean-sounding "burble" on decel, I haven't found any other benefit.
If you find a hesitation when getting back on the throttle, then check your idle switch-- it should barely trip with the throttle closed, then open as soon as the throttle is opened slightly.
![Cheers](https://rennlist.com/forums/images/smilies/beerchug.gif)
If you find a hesitation when getting back on the throttle, then check your idle switch-- it should barely trip with the throttle closed, then open as soon as the throttle is opened slightly.
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#57
Nordschleife Master
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Yes, I am aware of that.
That makes sense. Fuel consumption is not on the top of my list, especially since it's already so low.
I can hear the exhaust sound difference, yes.
Here's the other benefit. Repeat the following experiment on highway with the fuel cutoff enabled and disabled. On a high gear, let the car decelerate down to 2000 rpm. Then floor the pedal as quickly as you can.
What I am finding that with the fuel cutoff enabled, the car hesitates but with the fuel cutoff disabled it doesn't.
If one doesn't floor the pedal instantly and instead rolls to wot a bit softer, there's no hesitation with either setting.
The throttle position switch works correctly, that's not what this is about.
By "kill the car" do you mean damage the car or kill the engine in the sense of stalling it or making the ECUs think it has stalled?
Why do you only disable the fuel cut off after start up? Why not leave it disabled all the time?
That makes sense. Fuel consumption is not on the top of my list, especially since it's already so low.
Here's the other benefit. Repeat the following experiment on highway with the fuel cutoff enabled and disabled. On a high gear, let the car decelerate down to 2000 rpm. Then floor the pedal as quickly as you can.
What I am finding that with the fuel cutoff enabled, the car hesitates but with the fuel cutoff disabled it doesn't.
If one doesn't floor the pedal instantly and instead rolls to wot a bit softer, there's no hesitation with either setting.
Why do you only disable the fuel cut off after start up? Why not leave it disabled all the time?
Last edited by ptuomov; 08-23-2010 at 03:54 PM.
#58
Nordschleife Master
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I searched the web for this, and for each ten hits I got eleven explanations. This one is my personal favorite:
http://www.ehow.com/how-does_5545351...le-causes.html
Exhaust Burble on Deceleration
An exhaust burble, or throaty popping noise which could be likened to a babbling brook, is has a different cause if it only occurs when suddenly backing off on a vehicle's throttle. Essentially, the sudden easing off the throttle causes an immediate decrease in exhaust emissions to the degree that atmospheric pressure surrounding the exhaust pipe pushes cool air up into the exhaust system. This air collides with the warm exhaust gasses and creates a rumbling not unlike thunder. Normally this will only happen if the tailpipe has too wide a diameter to maintain equalized air pressure, or there is a seam in the exhaust pipes which is not air tight.
Exhaust Burble on Deceleration
An exhaust burble, or throaty popping noise which could be likened to a babbling brook, is has a different cause if it only occurs when suddenly backing off on a vehicle's throttle. Essentially, the sudden easing off the throttle causes an immediate decrease in exhaust emissions to the degree that atmospheric pressure surrounding the exhaust pipe pushes cool air up into the exhaust system. This air collides with the warm exhaust gasses and creates a rumbling not unlike thunder. Normally this will only happen if the tailpipe has too wide a diameter to maintain equalized air pressure, or there is a seam in the exhaust pipes which is not air tight.
#59
Rennlist Member
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Stalling it. rev the engine up to 6000 after it is hot and have been running at WOT, and let the throttle off. you will stall it, or have it stumble at least.
I dont use it on start up, as the system is very good at stablizing the idle. after it warms I turn the stock system off. even when hot, with it engaged, the immediate starting idle run up runs the rpm up higher than with the stock system engaged.
So what exactly causes the burble on deceleration? Is it some cylinders having lean misfires, then the unburned air-fuel mixture burning in the exhaust? Or is it rich misfires? Maybe it is timing being retarded and burn slow enough that the mixture is still in the early stages of burning when the exhaust valve opens?
I searched the web for this, and for each ten hits I got eleven explanations. This one is my personal favorite:
I searched the web for this, and for each ten hits I got eleven explanations. This one is my personal favorite:
#60
Nordschleife Master
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Stalling it. rev the engine up to 6000 after it is hot and have been running at WOT, and let the throttle off. you will stall it, or have it stumble at least.
I dont use it on start up, as the system is very good at stablizing the idle. after it warms I turn the stock system off. even when hot, with it engaged, the immediate starting idle run up runs the rpm up higher than with the stock system engaged.
I dont use it on start up, as the system is very good at stablizing the idle. after it warms I turn the stock system off. even when hot, with it engaged, the immediate starting idle run up runs the rpm up higher than with the stock system engaged.
My problem is that I don't understand how the LH 2.3 DFCO function works. Other ECUs from the period have load and rpm thresholds when to cut fuel. They also have a block-out period, of the order of 10s, during which the DCFO doesn't activate a second time right after the first time. Finally, some of them have an alternative, deceleration enleanment, which will lean out but not shut off fuel when it's not quite clear what the driver wants.
Those other systems typically turn the fuel back on after the revs drop below some threshold. The threshold is somewhere between 1000 and 2000 rpm, I think. So, as long as the ECU detects stall only based on the engine speed (say going under 500 rpm), it would be hard for the DFCO to cause stalling, at least on those systems.
For the same reason, I am having a hard time understanding how having DCFO enabled or disabled is going to influence the idle stabilization. If the DCFO is not active below say 1100 rpm (drawing this number from my hat), it will not get invoked during idle unless the idle spikes to above 1100 rpm. Also, if there's block-out period of 10 seconds, DCFO couldn't function as an idle stabilizer anyway.
Or are you saying that the DCFO is somehow engaged immediately after cranking? That would be a stupid system, and I am having a hard time believing that this how they programmed it.
I am not challenging your observation, just trying to understand what causes it.
One more observation: At least with my car, the car sometimes stalls at idle if I set it up to be too rich. This from either the base map or the warm-up compensation / enrichment map if I recall correctly. I don't think it has yet stalled because of running too lean. In my experience, the problem with too lean is not stalling but the transitioning to higher load is less smooth. I may be totally confused about this, since I am learning about the ECUs largely by trial and error.
Those int he know may want to chip in.