Air in Bosch pump.....possibly?

BX Bandit · Post by **BX Bandit** » Sat Sep 30, 2006 5:31 pm

About a year ago, I exchanged my Rotodiesel pump (which was knackered) for a used Bosch unit from a 1.7TD. On the whole it goes well but there is a minor problem which I can't get to the bottom of...

On start up, from cold or hot (after being turned off for a few minutes plus), the revs are low by about 200rpm. Over the proceeding 60 seconds or so, the revs slowly rise back to 1100 ish when cold or 900 ish when hot.

I have experienced air in a rotodeisel, but having read various posts on this subject, it seems that air may affect the Bosch in different ways. Could the above description be indicative of air seeping in then being purged out somehow? It also takes up to 3 seconds to start without preheat when hot.

None of the above symptoms occur when starting up immediately after switching off.

Any ideas - it's not causing a real problems apart from my mental health - I hate even the slightest mechanical fault

jeremy · Post by **jeremy** » Sat Sep 30, 2006 5:54 pm

The Bosch will be affected by poor leakoff pipework - which won't affect a Roto-Diesel (which just leaks and smells.)

BX Bandit · Post by **BX Bandit** » Sat Sep 30, 2006 6:01 pm

Thanks Jeremy,

I think the leakoff pipework is OK, it was new when I replaced the pump - could be worth replacing tho'. If it was leakoff pipes, what are the symptoms in the Bosch pump?

I swapped the injectors for new Bosch ones. The only original Roto part is the fuel filter housing/priming pump, could that make a difference - I assumed not....

jeremy · Post by **jeremy** » Sat Sep 30, 2006 6:30 pm

Fuel filter should make no difference at all. Early pumps used either Purflux or Roto-diesel filter units which simply filter the fuel and provide a primer pump with an external fuel heater on the back of the engine. Later ones use the black plastic device over the thermostat - which has its own problems - like leaking thermostat which lets air in.

Leakoff pipes will let air in with the fuel on a Bosch pump - bad starting, irregular running . . . - Check the cap on the last injector - having just had one fail on me after a year on our ZX. (Roto-Diesel pump - just leaks and smells)