I've got my first Volvo a 98 s90 from a family friend. It used to run nice but after he pulled the engine and replaced the freeze plug the engine failed to spark after cylinder 1. He checked for any pinched wires but didn't find any. That's when I was given it. I checked the rpm and cam sensors for proper signal, and they're good. I'm now at a brick wall for what to check next.

 

I'm not a mechanic but I have replaced the wiring harness to the ignition coil packs on my 94 960 sedan 2.9 engine.

Just a thought, are you sure it's no spark on any other cylinders after #1? Or might it be no spark on 2,4,6 which could indicate that one of the two ignition modules, which sends signals to 1,3,5 is working or partially working, and the other module is not sending signals to 2,4,6?

UPDATE Jan 28th 2022.: If you get good aftermarket modules, they are not expensive (up to about $45 each vs. OEM Bosch about $200 each) and both modules are the same part number. I can vouch for one that is branded as "HUCO" I've used them on my 94 960 and they work fine for me and they've lasted for years. I don't think that I would buy one off of Amazon.com for $14.99 though, except it would be good for swapping in to see if you get spark. Might not last forever but maybe it would, who knows? Just saying there are others besides Bosch brand for $200 each. Try FCPEURO.COM and IPDUSA.COM for example, also I saw the one branded HUCO on Amazon.com for approximately $40.