I recently upgrade my P3 with an IDE to compact flash adapter. I had no issues, so I thought I'd try it out on my 486 machine.

Specs:
486 DX 2
4DMU-HL3S Motherboard
VLB I/O Card
Diamond Speedstar Pro VLB Video Card
Media Magic ISP-16 (with IDE CD ROM)

I'm using this adapter:
https://www.amazon.com/StarTech-com-Single-Ad … 05069407&sr=8-3
And this CF card:
https://www.amazon.com/Verbatim-2GB-CompactFl … ps%2C154&sr=8-3

The adapter is the same as the one in the P3 system, but the CF card in the P3 is a 32GB Transcend card

The problem:
The bios correctly detects the card as 2gb, I can partition it with fdisk, format it with format /s (504mb), boot to it, and even install dos 6.22. When I try to install Windows 3.11, or just copy a disk full of files over, it encounters various write errors, drive not found, etc. The HDD light is stuck solid when this occurs. Retrying works sometimes, but usually results in a corrupted file being written. I accidentally bought 2 of the 2gb CF card, same behavior with both. I also found another IDE CF adapter lying around (I think it's this one https://www.amazon.com/StarTech-com-Pin-Compa … 05070001&sr=8-4) and still the same behavior. I tried changing the various IDE settings in the bios (block mode, wait states, lba, 32 bit) but the iteration time to fully test each setting was a bit long and I lost track of exactly which permutations I tried. All I know is nothing worked.

I found a 8GB hdd to sanity check, did all the same steps, and so far so good, Windows 3.11 is installing as I type this. So I don't think it's the IO card.

I've got an SD to IDE adapter en route, as well as another transcend CF card to try out. I'll report back with results.