[skyship007]

Originally Posted by bobthecabbage

Broke down and then won't start is a bit different to plain 'won't start'.

So many possibilities that without ruling something out you'll never get to the bottom of it.

Other than a code read starting with the basics such as ensuring air free fuel is being drawn up from the tank. You could bypass the fuel filter and allow the engine to suck up some clean diesel from a clean container along the lines of this epic video (use an in-line filter to protect your system).

https://www.youtube.com/watch?v=xYsXHC2-PSw

Or just fit a section of clear fuel pipe so you can see if air free fuel is being drawn up. A few small bubbles shouldn't be an issue.

I agree, but if you have to use the priming bulb to get it to start, then it's worth chasing the source. Odds on, one of the 2 fuel filter O rings is split or even missing.
Not sure if the OP has even changed the filter yet!

If you block the air filter, the engine would start and then fail giving a fault code. Might be the same as a MAF sensor code.

PS: Just watched the linky, OMG it's got a 5 liter can of Liqui Moly Diesel Purge (Direct feed or in tank injection system cleaner). Which fleet of buses are you cleaning up ??