Most 1989's came with the -561 unit, and it was troublesome in it's original form. Reportedly rebuilts are OK. The 1990-up -951 unit is a direct replacement and a good bet for an upgrade.

However.... it's not the MOST likely thing to kill the car. It's one of the top three, but... you ought to replace the fuel pump relay, or if you've got soldering skills, pop it open and resolder all the large connections inside it. A new one is ~$20 from suppliers, about $40 from Volvo.

There's also a sensor that provides impulses to the ignition and fuel computers, mounted in a tough spot over the top of the transmission, but it too can cause the car to quit abruptly.

Pull the coil wire and find out if you've got spark- I remove the dist cap end, and tuck it in by the left hood hinge. From there you can observe whether it makes a strong blue-white spark while turning the key.

If there's spark, it would rule out the RPM sensor/crank sensor unit, as well as a bunch of other ignition parts. The other items would still possibly be at fault.
Good luck!
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Rob Bareiss, New London CT ::: '87 244DL/M47- 229K, 88 744GLE- 218K, 82 245T-181K Also responsible for the care and feeding of: 88 745GLE, 231K, 87 244DL, 239K, 88 245DL, 246K