Forbito Posted May 22, 2014 Share Posted May 22, 2014 This has just happened during a competition, about 250 miles after installation. The engine had begun to have difficult starts a couple of hours before, the ECU activated the pump relay intermittently and I was able to start it only at the second attempt. The wiring loom has been correctly built, everything ran well until disaster... The ECU has been always protected by a 3 amp fuse. The blown transistor is the Q16 and if I understand correctly it is the only component that drives high current. Apparently any other component in the MS1 board is damaged, so it could be easely replaced. But I would like to understand what went wrong and avoid to meet up with another blown transistor after a couple of days... Is there something that I have to check considering the internal damage? Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted May 22, 2014 Share Posted May 22, 2014 Although it's in the Q16 slot, that is the fast idle / PWM idle valve driver transistor. This switches the ground wire of the PWM idle valve, and as such is not protected by your 3A ECU fuse (the ECU's 12v supply only powers the ECU itself, the injector power, fuel pump relay feed and idle valve are all ground-switched by the ECU so should be protected by their own fuses). The transistor is a TIP122FP, any TIP122 will do but metal-tab types must be mounted with an isolated mounting kit. Quote Link to comment Share on other sites More sharing options...
Forbito Posted May 22, 2014 Author Share Posted May 22, 2014 Ok, thanks for your help. The power source of PWM valve was protected by a fuse, but it was evidently too large. But my doubt is: can the failure of PWM circuit, alone, make the ECU unable to run? Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted May 22, 2014 Share Posted May 22, 2014 It's hard to say without testing the ECU, there could be other damage not visible. Quote Link to comment Share on other sites More sharing options...
Forbito Posted May 24, 2014 Author Share Posted May 24, 2014 My theory is: the PWM transistor probably blown quite soon after the first installation, and this would explain why the valve did never work, manteining the idle costantly high, at about 1400rpm. I would have done better to check first to understand the reason of this, but I had postponed the inspection to after the race (I never have enough time!), focusing on tuning and keeping the valve blocked once the engine was warm. The car ran perfectly until the race. Then, the death of the MS1 has been caused by something else, almost certainly an internal failure (because the ECU remains off and doesn't communicate despite that there is not any interruption in the power supply and in the ground wire). It's not clear if it depends on the burning of the PWM transistor or not. The failure seemed to occur progressively: first difficult startings, but once the engine was running any malfunctioning disappeared, then it died during the race and without any warning. This could be a clue, but I have no idea on how to interpret it. Quote Link to comment Share on other sites More sharing options...
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