Really enjoying the steam → diesel → electric ladder, thanks for keeping these going.

Running 0.5.4 under pyanodons I hit two issues that make the locomotive close to unusable there. Both are one-line-ish fixes and neither changes vanilla behaviour, so I've included patches in case they're useful.

1. Every fuel except coal is ejected into the player's inventory

Repro: put any pyanodons chemical-category fuel (coke, etc.) into the firebox. It's accepted by the burner, then on the next update it's raked out and handed back to the nearest player — or spilled on the ground if nobody's nearby.

Cause is the allowlist in control.lua:

local FUELS = {
    coal = 190 / 216,
    wood = (190 * 0.8) / 216,
    ["solid-fuel"] = 190 / 216
}

used as a validity gate:

if slot1.valid_for_read and not FUELS[slot1.name] then
    ...
    eject_item(loco, name, count)
    slot1.clear()
end

Any item not named there is rejected regardless of whether the burner accepts it, so overhauls that add their own fuels lose them.

Since 2.0 fuel inventories hard-reject items whose category the burner doesn't carry, anything that reaches slot 1 is already known-burnable — the allowlist is doing a check the engine has done. Suggested fix: keep the table as tuned ceiling overrides rather than an allowlist, default everything else to coal's ceiling, and restrict the ejection branch to the daredevil fuels. Coal/wood/solid-fuel keep their exact current speeds.

2. Wood can't be inserted at all under pyanodons

Different mechanism — no script involved. prototypes/entities.lua hardcodes:

burner.fuel_categories = {"chemical"}

but pycoalprocessing moves wood into a new biomass category (prototypes/updates/base-updates.lua) and widens the vanilla locomotive to {"chemical", "biomass"} (prototypes/updates/entity-updates.lua). A chemical-only firebox therefore refuses wood at the slot.

Suggested fix, in data-final-fixes.lua — mirror whatever the vanilla locomotive ended up with:

local steam_loco = data.raw.locomotive and data.raw.locomotive["tp-steam-locomotive"]
local vanilla_loco = data.raw.locomotive and data.raw.locomotive["locomotive"]
local steam_burner = steam_loco and (steam_loco.burner or steam_loco.energy_source)
local vanilla_burner = vanilla_loco and (vanilla_loco.burner or vanilla_loco.energy_source)

if steam_burner and vanilla_burner and vanilla_burner.type == "burner" then
    local categories = vanilla_burner.fuel_categories
        or (vanilla_burner.fuel_category and {vanilla_burner.fuel_category})
    if categories and #categories > 0 then
        steam_burner.fuel_categories = table.deepcopy(categories)
        steam_burner.fuel_category = nil
    end
end

This needs no optional dependency — overhauls do this work in data-updates, and data-final-fixes always runs after every data-updates pass. In vanilla it's a no-op (copies {"chemical"} back onto itself).

Notes

• Worth knowing: pyanodons also files rocket fuel under a jerry category, so the rocket-fuel daredevil path simply never triggers there — the engine rejects it at the slot. Nuclear fuel stays chemical, so that one still works.
• I've been running both changes locally without trouble, but I haven't playtested the balance implications of non-vanilla fuels all sharing coal's speed ceiling — that's a judgement call that's yours to make, and deriving the ceiling from fuel_value instead would be the obvious alternative.
• Happy to send the full unified diff against 0.5.4 (also touches changelog/info.json for a 0.5.5 bump) if that's easier than patching by hand — just say where.

Thanks for this. I'll run it into the code and see if anything bad happens my end

Both spot on, and the diagnoses saved me the digging — thank you. Fixed in 0.5.5. The allowlist is gone: it was re-checking something the engine already guarantees, exactly as you said. Fuels without a hand-tuned speed now derive their ceiling from fuel value relative to coal (capped, and floored so nothing crawls) rather than all sharing coal's — coal, wood and solid fuel are unchanged. The firebox also mirrors the vanilla locomotive's fuel categories in data-final-fixes, so wood works under py again. Amusingly, if py puts jerry on the vanilla locomotive, that mirror hands it to us too — so the rocket-fuel surprise may find you after all. No need for the diff; it was a small change and I wanted to walk each line myself.