A stock 24 pin chip can be installed into the 28 pin ZIF socket, once the stock chip is removed from the original holder. I would try a stock chip in the 28 pin socket and see if it makes any difference in the way the engine will run. When installing a 24 pin chip into a 28 pin socket, PINS 1,2 27, & 28 are open. It's also possible to install a chip backwards into a 28 pin socket, VERIFY PIN 1.

If a chip is incorrectly programmed, the engine will run in a limp home mode (too much fuel).

We are assuming the 28 pin ZIF socket was correctly modified for the EEPROM and correctly installed into the '7747?

dave w