Originally Posted by mcbear
I just found the Megasquirt thread on Benzworld [although it seems I live on BW]. I have a small restoration shop here in Kentucky and one of the projects that we are working on is a 1993 500E. We are looking for performance gains, clean workarounds for the ASR defeat [although we can do that] cooling assistance and ECU options as we move to a 6Sp manual tranny for the car.
I know the ECU technology on the 500E is from 1984 or so and there has to be some performance/economy gains available if looked at correctly. My problem is I am just not familiar enough with programmable ECU work and changing the EFI to address that from the get go.
Reading your posts I understand you have a headstart. Any enlightenment would be appreciated on the M119 motor.
I want you to know that I am not an automotive tuning professional I am a systems programmer with an interest in cars. I own a 1980 450slc which I have become pretty familiar with over the years but I have no other Mercedes experience. Other Mercedes of this era have very similar engineering and fuel systems. I have no familiarity with a 1993 500e and do not know what type of fuel injection system it uses. If it uses a K-Jetronic (CIS) or D-Jetronic fuel injection system I might be able to talk to you about it with some level of knowledge. Do you know if your fuel system is a CIS type system?
From what little knowledge I have of computerized fuel injection systems they work on a very simple concept. A computer opens a fuel injector to allow fuel to flow through then closes the injector after a set amount of time (It pulses the injector). Most computerized fuel injection systems build on this basic concept by predicting how much fuel the engine will require based on a series of measurement. On megasquirt these measurements are RPM, MAP (manifold absolute pressure or simply vacuum), The temperature of the incoming air IAT, The temperature of the coolant CLT and the position of the throttle TPS.
With Megasquirt the two major variables from the list above it uses to calculate the amount of fuel required by the engine are RPM and MAP (The speed of the engine and the load on the engine measured by vacuum). The other variables are used fine tune the required fuel value derived from these variables. The power of the MegaSquirt computer is its ability to compute a complex equation with these variables in real time.
Another major feature of Megasquirt is its ability to use feedback from the engine to further refine the required fuel calculation. Most Megasquirt users pair their Megasquirt with some sort of wideband O2 sensor. An O2 sensor sits in the exhaust stream and will tell you if you are running rich / lean / or right at stoic (14.7:1) by analizing the burnt / unburnt exhaust gasses. A wideband
O2 sensor has the additional capability to tell you what the actual air to fuel ratio (AFR) is which means it will tell you how rich or how lean your mixture is and let Megasquirt know how much of a change it needs to make to the calculated value.
Megasquirt II also has the ability to let you set ignition timing based on the same variables listed above. This allows you to run a much more aggressive timing curve than you could with centripetal advance or vacuum advance resulting in more power.
You might already be familiar with all of this in which case I am sorry if I am patronizing you.
Most of MegaSquirt functions are also handled by other aftermarket ECUs. So what makes MegaSquirt different? What MegaSquirt has going for it that the other after market ECU's don't is the shear number of genius level people working in collaberation to make MegaSquirt the best ECU available. There is NO other ECU out there that has the level of MotorHeads, Tuning specialists, Engine Builders, Electronic Engineers, Computer Engineers and Programmers working together (and frequently argueing) that MegaSquirt has. This open source expertise just can not be matched by any private ECU venture out there. One of my favorite MegaSquirt features is XTAU. When I first read about XTAU correction I was simply amazed. The XTAU correction formula calculates via a user supplied variable the amount of fuel that is left on the walls of the intake manifold and isn't available to power the engine for a particular stroke but will be available to power the engine on future strokes. I have never turned on the XTAU correction feature and I really can't imagine using it. But I was simply amazed to find out that it exists in MegaSquirt and several people took the time to turn it into a practical tuning parameter. This sort of fine tuning is way beyond my capability but it is nice to know too what level Megasquirt is capabile of going.
Personally I am very confident that my Mercedes is running at a level of tune much better than it was ever capible of from the factory. At the same time I have yet to install a working TPS (throttle position sensor) and tune the engine for optimal power during acceleration. Did I mention I have no formal automotive background? I am amazed at the level of performance I have been able to achieve with my very limited knowledge. I am sure one of the knowledgable tuners could find all sorts of power in my engine that I have no clue about but I am still very confident that my engine was never capable of running as well with the stock K-Jetronic system as it does currently with my MegaSquirt implementation.
I hope you don't mind me posting this on the public board to share with others? Do you have any specific questions about Megasquirt?