IntroductionI want to give people a little overview of what a "Stage 1" tune is and just describe the general approach to chip tuning.
One of my cars is MY2000 Opel Omega-B 2.5TD, and I will use this one as an example.
What makes these cars a little special, is that the engine is lifted from a BMW. It is the intercooled version of M51D25, slightly detuned.
In return, BMW's using this engine are fitted with GM's AR35 automatic transmissions.
However, Opel in their infinite wisdom used the AR25 box on the diesel and the AR35 on their petrol engines. The 25 and 35 are just torque limits - 250nm and 350nm accordingly.
I bought the car with a blown trans for peanuts, and luckily the only difference between the AR25 and AR35 are uprated internals. So I acquired an AR35, retained the torque converter and bell housing from the AR25 and hey presto, I have a transmission that can handle 350nm. After fixing the boost leaks (the intercooler on this Omega was like swiss cheese) the car can be tuned for more torque and power.
First step was to find the ECU and check how boost is controlled.
The ECU turned out to be in the fusebox under the hood, and just slides out. The connector is a typical JPT-55 used in most Bosch applications of the 90-s (remember, the engine was developed in 1991!), and the control unit itself is a Bosch MSA-11 type or in other words - ancient by even 2000's standards when the car was built. Forget any flashing, only the manual approach will lead to results.
Around the turbo there are no fancy solenoids - the boost is mechanically controlled by a spring to about 1.2-1.3 bar.
Inside the ECUTo open the ECU, a series of tabs must be unbent. The rear ones are a bitch, and it will take a while if you are doing it for the first time.
Once the casing is off, two boards are revealed. These boards are connected together by a flat ribbon cable and can be separated at the back, however there are a bunch of T8 and T20 screws that need to be undone for the ECU to come apart:
- Four T20's under the ECU
- Four T8's by the connector of the ECU
- Two T8's inside the ECU under the cover
Once those are off, the entire assembly slides out.
Splitting the two boards reveals two chips soldered to the top board, marked "1 037 355 974" and "1 037 355 975", which contain the software, that needs to be tuned.
Of course, since they are soldered in, they first have to be de-soldered and sockets soldered in ("socketing the ECU").
Both chips are 27c256, 32kb UV erasable EPROM's and the main processors are 8051 derivatives.
Operation of the MSA-11 ECUBefore doing something inside the ECU one needs to understand why every change is made. The operation and algorithms of the ECU must be understood to reach a good result.
Most diesel ECU-s employ a similar control strategy. All the more modern units have their roots in the old MSA ECU's.
There are three primary inputs and one primary output that are linearized (obviously these are not the only ones):
- RPM - taken from some sort of trigger wheel, this lets the ECU know how fast the engine is rotating.
- TPS - driver throttle input, taken from a potentiometer at the throttle pedal.
- Mass flow - taken from a mass airflow sensor, to let the ECU know how much air is entering the engine.
- Pump control voltage - this is the primary output, which is used to drive the high pressure pump. It is linearized based on RPM and requested Injection Quantity, so that the ECU knows what voltage it has to supply to the pump to get a certain amount of diesel fuel into a cylinder.
Since boost is controlled mechanically, the only thing the ECU controls is when and how much fuel is delivered, and in simplified terms fuel equals torque in a diesel engine.
The fuel injection quantity (or IQ) is based on the driver pedal input, then limited by the MAF to prevent excessive smoke and also limited by a torque limiter to prevent mechanical failure.
As mentioned before, on the hardware side of things there are two main processors. The first processor calculates the required IQ and the second one takes that IQ and interfaces with the pump.
The chip with the lower software number contains all the calibration data and logic for determining IQ (plus a few other things, like glow plugs etc) and the chip with the higher number has calibrations for controlling the pump, including timing of injection start.
Mapping the MSA-11Now that we have some theory down, let's get down to business.
I only removed the chip containing the IQ calibrations, because the SOI (start of injection) is pretty decently calibrated from factory, and since I am not going to modify the pump voltage map, I have no need to modify these calibrations (more on that later).
After reading the chip in a programmer, the first step is to find the master table. The master table contains the address references of all the other tables and it is a series of addresses.
It's generally pretty easy to find just flicking through the file with a hex editor, or you can write an automated tool that would look for ten 16 bit addresses in a row...
Anyway, the master table for this file is at 0x74D0:
Now we just have to start looking through all the addresses and as a start find the large 3D maps.