I've been having problems with the wife's 406 2.1td not running properly (this has a fully mechanical Bosch from a 405td fitted),
it seemed like a blocked filter so I changed it, this was the start of the problems.
After changing the filter I couldn't bleed the air out, this was tracked down to the fuel return part of the pump being blocked, with what looks like the sticky stuff you see on the side of a deep fat fryer.
So I got a replacement pump off panelbeater (240m round trip) and fitted it, it now runs but it wouldn't rev past 3k,
this turned out to be the filter housing blocked up with gunge, reducing the flow (this was obviously the original problem).
with this all cleaned out the engine ran fine on tick over and revved happily, but when driving it's pulling air in,
this I have tracked down to the pump shaft seal.
I have a new seal but can't fit it for a few days now as I'm back to work tomorrow.
I've brought a new seal kit for the old pump, so when I strip it down I'll take photos of the crap inside, this pump has done almost 90k on bio so it'll be good it see what long term bio use does to them.
I explained that the pump had blocked up to the diesel specialist I got the seals from and he said "that's what happens with bio, it's normal for pumps to go like that".
I'll post photos of the crap in the housing and in the pump it's self, I may even do a wiki page on the long term effects of bio use.
It's worried me as to what my merc pump looks like inside.