[Vwdiesel] Fuel system check valves

Patrick Dolan pmdolan at sasktel.net
Fri Apr 17 05:02:58 PDT 2009

Don't expect to ever eliminate the bubbles in the fuel line.

ALL liquids at atmospheric pressure contain dissolved air and other gasses.  Just the mere act of moving them through the little fittings in the fuel system is often enough to liberate some (think of taking the cap off of a carbonated soft drink).

This is an incredibly important thing for any diesel enthusiast to understand.  It is one of the reasons that our engine technology lagged so far behind gassers for a century.  All of that liberated air gets through the pump and enters the lines to the injector, and must be compressed before the injection event can take place - resulting in differences in injection quantity at the cylinder and differences in timing between what the eingine THINKS is happening mechanically and what IS happening in fact.

Very few systems have ever dealt with this massive variable successfully.  If you look at #3 injector on a VE pump TDI, you will see how VWs suppliers cleverly did so.  The needle lift sensor in that injector tells the computer EXACTLY when that one opens, and adjust the timing for all cylinders to compensate.

HPCR engines don't have any such concerns because from the time the fuel gets to the high pressure pump, the fuel system pressure stays above miscibility level, so nothing can break the solution.  Result: possibility of exceedingly accurate timing (which today's piezo injectors can utilize).

Sorry for the lecture, but this is what I do for a living (make equipment that degasses petroleum).

----- Original Message -----
From: Terry Briggs <vbriggs at stny.rr.com>
Date: Thursday, April 16, 2009 2:27 pm
Subject: Re: [Vwdiesel] Fuel system check valves

> I've got line now, I'll spend saturday running lines and see where 
> that  
> gets me. Thanks for the direction and ideas,
> Terry
> On Apr 15, 2009, at 5:42 PM, LBaird119 at aol.com wrote:
> > In a message dated 4/15/2009 3:17:41 PM Central Daylight Time,
> > vbriggs at stny.rr.com writes:
> >
> >> I even get air
> >> bubbles on the filter side of the line when priming things with the
> >> mity-vac.
> >>
> >
> >   Leaks on both sides of the pump will end up with bubbles on 
> the inlet
> > side of the pump.  :-P
> >      Loren
> >
> >
> > **************
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