I recently finished up a Gen 4 5.3 / 4L60e swap in a 1979 chev pickup. No modifications to motor or trans. Engine, trans and ecm /tcm were all from the same donor vehicle. I?m having a really strange problem and it seems I might be the only person in the world to run into this because nobody seems to have an answer. I don?t even really know what to search for to help find the answer but I?ve been looking all over the place. It?s like my truck has 2 different modes. One - which we will call the bad mode - where it runs ok but only revs up to about 2400 although shifts through the gears properly - actually runs ok just no power - maybe limp mode but I?m not sure because it still shifts through all the gears. The other mode we?ll call the good mode where everything seems to work perfect and revs up like it should.
Every time I start the truck and drive it is in the bad mode and very rarely it will suddenly switch from bad mode to good mode while driving. I?ve spent countless hours trying all sorts of things to no avail then one day by accident I learned that if I log into the VCM Scanner and log out again it will always 100% of the time switch to the good mode and stay there until I shut the truck off. I can drive for a few hours in the good mode and it will stay that way until I shut the truck off. I can even log back into the scanner and it will still stay in the good mode.
Only changes I have made to the tune is VATS, DOD disable and gear / tire size. Anyone ever run into this before? E38 ecm with tcm that were all original to the engine and trans. Checked and double checked my wiring and it?s all good. Even if it was wiring it shouldn?t change to the good mode every single time I log in and out of the scanner.