I should start off by saying that I have never seen a 16V fuel pump system (I have a VW 16V in a different car with aftermarket injection). Bubbles can only be either air or vaporized fuel.
If they are air then it is being drawn in at the suction side of one of the pumps. If the pre-pump is working OK then the suction side of the main pump is pressurised and so can't draw in any air. This leaves the suction side of the pre-pump. Look for pin holes or splits in the hose or cracks in any hose barbs (and that all hose clamps are tight). If this was happening you would get the symptoms you have described. To check if they are fuel vapour bubbles from engine bay heat: Trap a few bubbles in a high point of the clear hose with the engine off. Dribble some cold water over the clear hose to cool the fuel. Fuel vapour bubbles will disappear completely when the temp drops below about 60C while air bubbles will shrink slightly but not disappear. Rick Dathan, Australia Ex - Message: 8 Date: Tue, 1 Apr 2003 22:17:57 -0800 (PST) From: Barney Culver <[email protected]> Subject: Re: [a2-16v-list] 16v problems HELP!!! To: [email protected], [email protected] Well...it could be that I got a bad pump but I just did replace it about a month ago along with the fuel filter. The main pump just sounds like it doesn't have a load on it when the problem happens. Another thing that I did notice was that the fuel line flowing back to the fuel tank (green and transparent on my car) had a bunch more slower moving bubbles in it when the problem was happening...maybe still a bad transfer pump???
