So I have a bit of an update. Fuso has rewritten the engine management software. Apparently it is originally Fiat software written in Switzerland. Who knew? Anyway Mitsu recognizes there is a big issue here and has had 40 or so engineers from around the world gathered in New Jersey rewriting the software over the last couple of months. A regional Mitsu rep installed the software in both of my trucks this week. The gist of the issue that I got was the software parameters were written with unnecessary tight tolerances to meet CARB requirements. I reviewed this thread and the service histories of the trucks with the rep and he felt that the issues that I have been experiencing are moisture related, but different than I suspected. In the original software the cat temperature sensor had to read high enough to allow a reburn. In very wet weather the cat would cool down and the reburn could not happen. This temperature variation and lack of reburn would de rate the engine and cause the codes I was seeing. The new software does not check cat temperature before reburn. This tells me this issue is/was widespread. He did allow that they had seen some issues with moisture intrusion into harnesses but that threw different codes. We discussed the transmission issues at length and said that had not been identified as a major issue. He suggested that our local hilly environment was substantially different than the norm and that was why we were experiencing the issue. He did not feel the software update would fix it. He agreed to document and forward the problem to engineering. I drove the 125 today and did not experience any major differences in driveability after the update. Wait till the rains return in the fall, then we will see.
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