I finally got the right upgrade -replacement EPROM (chip ) for the 561 computer in my '90 240 wagon.
The correct Volvo part number is 271838-6 on the box ( and just #271838 on invintory sticker) about $68.00 from Trollhattan auto parts.
I'ts not high performance but a definite improvement over the original.
Much better cold starting , smoother acceleration , and more power accelerating up hills.
also better gas milage in mountains /city.
it's so easy to replace that I'm keeping a spare along with an anti static strap and a chip puller in the glove box, and I taught my wife how to change it out in an emergency (takes about ten minuits).
Thanks again to all who helped .
---------Robert
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