Lemmiwinks: Difference between revisions

Revision as of 18:14, 21 January 2008

What is Lemmiwinks?

Named after an infamous Southpark character, lemmiwinks gives the average person access to a few parameters used by the Bosch ME7.1 to make engine management control decisions. While it does not allow the user to directly modify the internal boost/fueling/timing maps, let alone the control code responsible for interpreting those maps, it does allow quite a bit of customization.

Of most interest, it allows quite a bit of control over fueling, which, in the case of the B5 S4, is probably the single most important parameter when using a larger turbo than stock.

Of secondary interest is its ability to change the overall timing maps. However, ME7.1's built-in knock sensor control loop somewhat limits the usefulness of this feature.

In addition, Lemmiwinks allows changes to the speed limiter, parameters governing engine idle characteristics, and "specified load" scaling. This last function is unfortunately also of limited use. Even though target load is directly related to specified boost, the default value is 100%, so target load (and therefore boost) can only be scaled downwards, not upwards. However, reducing overall boost can help prevent boost deviation which can cause throttle cut.

Channel summary

Ch.	Name	Function	Increase/decreasing value result
01	Idle Speed Offset	Adjust idle RPM level	Increase/decrease idle (RPM)
02	Fuel Tweak (Accel Pump) - Increasing Loads	Fuel trim tweak while load is rapidly increasing	Add/remove fuel (%)
03	Fuel Tweak (Accel Pump) - Decreasing Loads	Fuel trim tweak while load is rapidly decreasing	Add/remove fuel (%)
04	Start Up Fuel Enrich	Fuel trim during engine start	Add/remove fuel (%)
05	Warm Up fuel Enrich	Fuel trim during engine warmup	Add/remove fuel (%)
06	Lambda Regulation	Controls narrow band 02 cycle time	Increase/decrease cycle time
07	Additive Offset To Speed Limiter	Speed limiter	Increase/decrease speed limiter (km/hr)
08	Secondary Fuel Tweak	Additive fuel term	Increase/decrease additive term (offset)
09	Ignition Timing Offset	Adjust overall timing	Advance/retard timing (degrees)
10	Primary Fuel Tweak	Multiplicative fuel term	Increase/decrease multiplicative term (%)
11	Unused	Unused
12	SEL Scaling (Turbo Cars Only)	Scale specified load	Increase/decrease requested boost (%)
13	Control Bits	Unused
14	Idle Torque Additive Offset	Controls engine load at idle	Increase/decrease spec load at idle

Bosch ME7.1, load, and you

So, how does the ECU decide on injector on time, boost, and timing? One word: load. The ME7.1 is a "requested torque" based control system, which basically means that all decisions it makes is based on what it thinks the driver is asking for in terms of torque. The B5S4 is completely drive by wire (a.k.a Electronic Throttle Control or ETC), which means there is no direct connection between the accelerator pedal and the throttle valve. All the accelerator pedal does is tell the ECU how much the driver wishes to "accelerate".

Fueling curve

Primary and secondary fuel tweak

To simplify things, from here on out will we assume the injector on time is ONLY a function of MAF readings. At its simplest, the fueling vs MAF value curve is a straight line with two terms. For those of you who know geometry and algebra, call it $y=a*x+b$ , where x is the MAF, y is the injector on time, a is the "multiplicative" term and b is the "additive" term. There are additional terms based on the slope of the MAF, but that will wait for later.

To "enrich" the fueling across the board by a fixed percentage, one would increase the a (multiplicative) term, so the fueling is increased proportionally for every MAF value.

For example adding 10% to 10 yields 11, for an increase of 1, but adding 10% to 100 yields 110, for an increase of 10.

The "additive" value b does not have as much an effect near the top of the curve, because it is additive. In other words, adding a small amount everywhere means that the percentage increase of fueling for "high" MAF values is much lower than the percentage increase for "low" MAF values.

For example, adding 1 to 10 (to 11) is a 10% increase, whereas adding 1 to 100 (to 101) is only a 1% increase!

What does this mean for lemmiwinks? It means that the primary (multiplicative) fuel tweak (channel 10) increases fuel across the board, whereas the secondary (additive) fuel tweak (channel 08) has almost no effect on fueling for high MAF readings!

You can see what the ECU's own base additive and multiplicative "tweaks" are by examining the long term (LTFT) and short term fuel trims (STFT) with VAGCOM (blocks 32 and 33 respectively) or ECUx. However, the ECU will only update these based on O2 sensor readings, and only during closed loop operation.

Fuel tweak increasing loads and fuel tweak decreasing loads

Now, lets talk about those other terms - channels 02 and 03: Increasing and decreasing loads. Basically, those terms "tweak" the basic y=a*x+b by multiplying the overall result by a term that is dependant on the slope (or derivative dx/dt where x is load and t is time) of the load. That means the faster the load is increasing (or decreasing) the more this term affects the fueling. So the faster the load is going up, the more the "increasing load" term will adjust fueling. Similarly, the faster the load is dropping, the more the "decreasing load" term will change fueling.

Note that load is rougly proportional to MAF/RPM. This means that load is "increasing" when MAF is increasing more than RPM, and that load is "decreasing" when the MAF signal is decreasing, or is increasing slower than RPM.

In real life terms, load is "increasing" during turbo spool up. Once max boost is met, RPM is generally increasing faster than MAF. In this region, load is actually decreasing!

EGT effects on fueling

EGT can effect the overall fueling. If EGTs are over approximately 980°C (1796°F) the ECU will add fueling (and possibly pull timing?) to bring the EGT temperatures down. This effect can be seen in VAG-COM block 112.

The functional range of the EGT sensor is 950°C to 1025°C (S4 2.7t Self Study Programme, page 47).

Block 034 does NOT measure real EGTs, it is only a calculated value based on maps using load/RPM as inputs.

Obviously, care must be taken when tuning the car under high EGT conditions, as the behavior of the ECU is radically different under "normal" conditions. A good rule of thumb is to try to get as much tuning as possible done under cool conditions and to make sure the intercoolers are not heatsoaked. Having an accurate picture of fueling and timing is critical to getting good results. Tuning your car under "artificially" enriched or pulled timing conditions simply means you run the risk of running lean or having too much timing under "good" conditions. The ECU will compensate using the knock sensor function, but it is better to get your car in the correct ball park for "normal" conditions.

Tuning with Lemmiwinks

More to come here. For now, check out Edy Jun's excellent Lemmiwinks Tuning Notes

How lemmiwinks works

According to Revo (the makers of Lemmiwinks):

Directly transferring the new adaptation channel values into the ECU works by finding the RAM memory location where the ECU stores the adaptation channel data and directly writing the changes to those RAM memory locations. When the ignition key is turned off the ECU enters a housekeeping mode where among other tasks the modified adaptation channel data is written into the serial eeprom. This roundabout method is required because memory writes directly to the serial eeprom are blocked.

Interestingly, this method will not work using the VAG mode protocol. Write access is allowed to any ECU RAM location except those locations that store the serial eeprom data. Someone at Bosch clearly knew about this vulnerability and took measures to close this loophole. But for some reason this loophole was left in the KWP2000 routines.

Each ECU code stores this adaptation channel data in different RAM locations. To make this method work with any ECU one runs through the following steps:

Establish communications with the ECU using KWP2000 mode

Read data directly from serial eeprom (since read access is allowed)

Search for this data in the ECU's RAM

Write the new adaptation channel settings to the RAM location

Cycle ignition key to have ECU transfer the new settings into the serial eeprom.

The KWP2000 protocol is not as reliable as the VAG protocol. Some cars will have communications problems which often can be worked around by pulling the instrument cluster fuse (make sure VAG-COM will be able to
clear your air bag DTC light before doing this!).[1]

@@ Line 73: / Line 73: @@
 So, how does the ECU decide on injector on time, boost, and timing? One word: [[load]]. The [[ME7.1]] is a "requested torque" based control system, which basically means that all decisions it makes is based on what it thinks the driver is asking for in terms of torque. The B5S4 is completely [[drive by wire]] (a.k.a [[Electronic Throttle Control]] or ETC), which means there is no direct connection between the accelerator pedal and the [[throttle valve]]. All the accelerator pedal does is tell the ECU how much the driver wishes to "accelerate".
+See also the [[Bosch ME7.1]] article.
-Based on that input, the ECU calculates a "target torque" that the user seems to be requesting. This, in turn generates a "requested [[load]]", which is capped by "specified corrected [[load]]" (a function of RPM, IAT and other limiting parameters, such as knock control, etc.). This requested [[load]] determins the throttle plate angle and requested boost.
-Once the ECU decides the requested [[load]] is large enough(?), its fueling control system goes [[open loop]]. In the [[ME7.1]] [[asynchronous path]], this means that all fueling decisions are going to be made almost soley based on [[Mass air flow|mass air flow sensor]] readings. Those [[mass air flow|MAF]] readings also go into the fueling maps as a "engine [[load]]" and are used to generate injector on times independent of O2 sensor readings.
-In the ME7.1 [[synchronous path]], the timing maps determine the timing at every cycle of every cylinder, and should the knock sensor for a given cylinder reach a certain threshold, the timing will be cut down for the next cycle for that cylinder. If the knock sensor activity subsides, the timing will be restored, one step at a time, until another knock event occurs on that cylinder.
 ==Fueling curve==