hi i stuck a 5.3 lm7 and the wire harnes and computer out of a 03 2wd yukon in my 99 chevy silverado that had a 4,1 the fuel pump come on just have no dash lights and no crank it works with a code reader and the security light came on i am working on my grounds plus the yukon had the 4L80 trans and my silverado has the 3L60 I used the plug from the 4L60 do you think this will work or am i waisting my time

Asked by Craig Feb 11, 2019 at 02:44 PM about the 1999 Chevrolet Silverado 1500 LB RWD

Question type: Car Customization

1 Answer

103,435

I think you are dealing with incompatibilities between the newer Yukons harness and your older truck, and no way is that newer engine computer going to work for that older tranny, it needs to be reflashed (assuming there is a factory setting that it can be flashed to). The engine computer is programmed for specific shift points based on gear ratios in both tranny and rear end. You'll also have to see what modules in the dash (like instrument cluster module) that need to play nice with the engine computer and what sensor inputs are needed for the gauges.

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