2003 mini After making sure the spark is there on all cylinders , I removed the electrical connection on each injector, cylinder 4 had no change in performance, all others killed the engine. Replaced the injector on cylinder 4 and no change. measured the resistance on the new injector, cylinder 3 injector and the original injector and they matched. measured the voltage and it had voltage on the injector. Ohmed the wires out from the injector to the ecu and supply block. Figured it was the ECU at the time. replaced ecu with a used and got it matched with the original via third party company. Ironically the dash lights started to work but still had issues with Cylinder 4 injector not working. I am considering replacing the camshaft positioning sensor, but not sure. These German cars are beyond different with most cars. Having to program a replacement ECU with your key and vin is crazy. I am not a mechanic but have rebuilt engines and have allot of knowledge too.
ok so you have the tritec engine first gen, very common on these for coil pack to break down with age, also if you pull the ht leads off the square coil pack you might find one corroded its common number 4 tends to do this can effect running to number 4,,
also worth removing the injector rail totally and crank engine while watching the spray patterns on them see if all atomise the fuel,, its possible the injector might be blocked,IF INJECTOR NOZZLE FAULTY OR BLOCKED WILL GET NO FAULT CODES, JUST A MISFIRE CODE.. try swapping the injector to another cylinder see if fault moves.
other common faults with those engines with some age and miles to them are head gaskets fail between cylinders or cylinder to oil crankcase, the valve springs go weak and dont seem correctly first time i had this it proper ran we around the block for a day checking and double checking,,
these days my very first job is compression test when engine is cold on cranking, and again with engine nice and hot,, see that got even pressures 100psi is very lazy and maybe battery a tad low, or common to find 2 cylinder side by side to have the same very low readings when gasket fails between the bores,, leak down test worth doing as well.
n 1997, Chrysler Corporation and Rover Group (then a subsidiary of BMW) formed a joint venture called Tritec Motors to design a new small straight-4 engine. The new company built a factory in Campo Largo of Curitiba, Brazil specifically to manufacture the new engine. The Tritec name stands for the union of the three countries involved: Germany, the United Kingdom, and Brazil.
When BMW broke up the remains of Rover Group in 2000, BMW kept the stake in Tritec Motors as the engine was in use in the Mini range which BMW had retained. In 2007 BMW sold its 50% stake to DaimlerChrysler and cancelled its contract for the Tritec engine. BMW entered into a new joint venture with PSA Peugeot Citroen to develop the Prince engine which is used in the second generation Mini cars just a bit of useless info but shows its not totally German