prj tuning

He who stops being better stops being good.

Archive for January, 2012


Tuning a Diesel


This post will be a little bit different to the one-car-per-post format. I 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 bar.
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