cencarnacion
Well-known member
I have an 02 Jetta ALH that has a stream of good-sized bubbles in the clear line between filter and IP when engine is revved up, none at idle. I am getting low mpg at around 32 and some loss of power. Vag com shows good actual boost/maf when compared to requested. Timing is okay. IQ is at set to 3. Vacuum at N75 is > 25 Hg. Air filter and snow screen clean. Did boost leak test and found no leak. Engine idles smoothly, does not sputter when revved up and starts right up.
What I've done so far to diagnose bubbles source.
1) Connected clear vinyl lines to fuel tank side of fuel filter and immersed them in a container with diesel, essentially a temporary tank, to rule out sender and lines to filter from tank as the source of leak.
Findings: Bubbles in clear line to IP. Some milky looking fuel going back to temporary tank. Can safely say there is a leak in filter to IP and back to filter section.
2) Swapped fuel filter along with tee with the one on my 00 Jetta ALH.
Findings: No help, same symptoms. Checked 00 Jetta ALH for bubbles at idle and revving and found none. High probability that leak is not in filter or tee.
3) Replaced both o-rings on filter tee. Applied vacuum to tee to check for cracks. No leak found. Moved tee and hoses to see if bubbles can be initiated. Could not.
Findings; No help. Same symptoms. Even higher probability that leak is not in filter or tee.
4) Removed both fuel lines between filter and IP and replaced them with clear vinyl lines.
Findings: Bubbles in supply line to IP. Return line from IP to filter show milky looking fuel going back to filter. Appears to be whipped up bubbles. Filter or tee cannot be ruled out but the whipped up bubbles from IP is suspicious.
5) Hesitant about introducing unfiltered fuel but did it anyway, bypassed filter by immersing both vinyl lines connected to IP directly into temporary tank.
Findings: No bubbles in supply line to IP. Return line from IP show milky looking fuel, again appears to be whipped up bubbles. Clear at idle. Rules out filter and tee since they are no longer in play.
Based on my tests above, I am thinking that the IP is pulling air from somewhere. Could it be from an IP seal leak? IP is dry, no leaks. Return lines from injectors back to IP are dry. Also, I read in a trucker's blog that air could be introduced through the injector nozzle itself when fuel pressure is lower than compression pressure thus forcing air into the nozzle. Can this perhaps be a cause too?
Before proceeding with changing IP seals and having injectors tested, I would appreciate ideas and suggestions from members in this excellent forum. Thanks in advance guys!
What I've done so far to diagnose bubbles source.
1) Connected clear vinyl lines to fuel tank side of fuel filter and immersed them in a container with diesel, essentially a temporary tank, to rule out sender and lines to filter from tank as the source of leak.
Findings: Bubbles in clear line to IP. Some milky looking fuel going back to temporary tank. Can safely say there is a leak in filter to IP and back to filter section.
2) Swapped fuel filter along with tee with the one on my 00 Jetta ALH.
Findings: No help, same symptoms. Checked 00 Jetta ALH for bubbles at idle and revving and found none. High probability that leak is not in filter or tee.
3) Replaced both o-rings on filter tee. Applied vacuum to tee to check for cracks. No leak found. Moved tee and hoses to see if bubbles can be initiated. Could not.
Findings; No help. Same symptoms. Even higher probability that leak is not in filter or tee.
4) Removed both fuel lines between filter and IP and replaced them with clear vinyl lines.
Findings: Bubbles in supply line to IP. Return line from IP to filter show milky looking fuel going back to filter. Appears to be whipped up bubbles. Filter or tee cannot be ruled out but the whipped up bubbles from IP is suspicious.
5) Hesitant about introducing unfiltered fuel but did it anyway, bypassed filter by immersing both vinyl lines connected to IP directly into temporary tank.
Findings: No bubbles in supply line to IP. Return line from IP show milky looking fuel, again appears to be whipped up bubbles. Clear at idle. Rules out filter and tee since they are no longer in play.
Based on my tests above, I am thinking that the IP is pulling air from somewhere. Could it be from an IP seal leak? IP is dry, no leaks. Return lines from injectors back to IP are dry. Also, I read in a trucker's blog that air could be introduced through the injector nozzle itself when fuel pressure is lower than compression pressure thus forcing air into the nozzle. Can this perhaps be a cause too?
Before proceeding with changing IP seals and having injectors tested, I would appreciate ideas and suggestions from members in this excellent forum. Thanks in advance guys!
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