Anyway to tell which part chest your missing?

[Striker]

I'm pretty sure I've collected all part chests in the game including ng+ and ng++ but still havent got the achievement

[REBirthTheEdge]

Fraid not.
You might need to consult a guide, I don't think there's a full on part count in the game.

[Mr.America]

If you're missing the AC parts achievement, try selling a random part and buying it back.

[BKo]

You have Ephemera chest? It's in depths 3.

[Striker]

Originally posted by Mr.America:

If you're missing the AC parts achievement, try selling a random part and buying it back.

It says all parts have been purchased but still nothing

[k-ricks]

game don't tell you can look in a guide tab and try to remember it

[...]

if you are following internet guides, it was probably in Depth 3. that was what i was missing when looking in the guide.

[(MP) Bud Tendy]

I had the same prob with AC parts achievement turned out the part I needed was from a battle log from some tetrapod hidden of the beaten path on the heli escort mission.

The good thing is it only takes about 20mins to speed run through all chest levels, you will only need to complete the missions that have any chests you missed
https://youtu.be/GHYrFfrJ8vI

https://youtu.be/0N4CcNyJmMM

[Emerald Lance]

Find a guide that tells you what each chest contains, then cross reference that against your inventory.