John Speake

Good info Dan - thanks.

ptuomov

I agree that my questions are perhaps more complicated than the average LH question here. I try to work out stuff on my own reading the ST2 manual and email friends for advice. Most of the questions simple questions get resolved this way. It's the more complicated and difficult (to me) questions that are left.

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.

That's exactly what I am planning to do. However, to do that, I need to have a ball park understanding of what each setting does. Otherwise, it's a hopeless needle in a haystack search.

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.

John Speake

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.

ptuomov

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."

ptuomov

The MAF sensor voltage is a non-linear function of the mass air flow. With some help from Jim Morton in terms of Bosch docs, and some spreadsheet work, here's my best guess of how the voltage relates to mass air flow.

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.

ptuomov

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?

WallyP

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%.

928mac

For those that can not visualize how it works
http://www.animatedengines.com/otto.shtml



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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

jcorenman

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.

jcorenman

You need a Sharktuner from JDS Porsche (a sponsor here). The EZK runs the ignition and the LH runs the fuel injection. Those are first-generation Bosch ECU's, no provision for computer interfacing other than simple diagnostics. The Sharktuner Mark-2 (ST2) for 87+ cars replaces the ROM's with flash-memory, allowing connection of a special interface box and a software program to give you access to the ignition and fuel parameters and maps. (You will also need a wbo2 for any serious tuning). Unless you are doing some mods the stock tune isn't bad, although a bit conservative.

mark kibort

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.

ptuomov

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?

ptuomov

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:

mark kibort

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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.

The burble , or backfires is due to fuel being igited in the combustion chambers. so quite the opposite, not lean, but there is fuel present. thats why the rpm falls much muchs lower when you lift with the off throttle circuit not being used.

ptuomov

When do the ECUs think that the engine has stalled? If it's rotating at 2500 rpm but misfiring on every spark, do the ECUs think the engine has stalled? Or is that determined solely based on the rpm?

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.