Ouch- that is ominous. My 91 has the same (either a 561 or a 951). I have one good spare though. I have noticed on the brickboard over the last two years an enormously higher rate of ECU problems with these cars. For comparison, I have never heard of a confirmed 86-88 car with an ECU problem that was confirmed by a qualified but not financially interested (dealer or money hungry/incompetent mechanic) party. It is just uncanny how regular the problem is if you look at a large number of 89 cars.

In fact, there are only three electronic things I worry about buying used from salvage yards when the cars are junked but not wrecked in a collision. The 89 ECU in question and the same from a B23 car along with its 002 AMM. Unfortunately, both these ECU's are in high demand. There is a roughly 50/50 chance a retired (not wrecked) car with these parts contains a dud unit. Fortunately, the pick and pull I visit refunds any defective part.