Fuel Blunder

[JohnD]

Not unless the engine is using fuel, which it won’t be if it isn’t running. Engine not running = fuel not circulating.

?Surely the fuel has to flow first, so the engine can start?

 

[Stivino]

?Surely the fuel has to flow first, so the engine can start?

It doesn't need to flow until the engine is running. The system is always charged.

 

[Harry Bloomfield]

What I did find out when I changed my lift pump was that it didn't actually run until the engine started - I wanted to see the new one run before I closed the tank off - which it didn't, the ignition switch did nothing and it wouldn't start, metered the plug terminals and nothing there - after much frustration and searching for relays and wiring faults I filled up the fuel filter housing - off she went!! I did wonder, with it being a fairly modern car, whether your supposed to do something in VCDS to run a priming sequence.

My diesel has a low pressure pump in the tank, a second one in the engine compartment, then a mechanical HP pump. The electric pumps run 45 seconds after the ignition is turned on, then off, unless the engine is started. It's a saddle shaped tank, so the tank pump serves the dual purpose of pumping to the front, as well as sucking fuel across to where the pump is located.

 

[cdbe]

Just had a quick Google, for VW there is indeed a process using VCDS to prime the filter housing, but it appears that manually filling the housing works as well - but not the usual cycling the ignition which we're used to.