blowing return lines - IDI Engine - VWDiesel.net The IDI, TDI, and mTDI source.

• blowing return lines by dillenger1 on 27 Dec, 2008 15:30
• I keep blowing off my cloth lines on hard pulls.Whats up?I thought the return need to be restricted.My feed from tank is 1/4"id stainless tube my return is 1/4"od,so it is quite smaller.
• #1 by jtanguay on 27 Dec, 2008 17:17
• i wonder what your internal pressure is to blow those cloth lines?
• #2 by jtanguay on 27 Dec, 2008 18:59
• i know someone running a 'closed loop' system right now... it consists of an electric feed pump that brings the system to a minimum of 4.7 psi or 7 psi max.   the return on the pump is sent back to the filter and back into the engine... the feed pump sends fuel to the filter.  it actually runs good! it starts REALLY good too... the way i see this working is that the pump auto corrects its internal pressures anyways, and the feed pump will only introduce more fuel that is burnt during combustion.  now a system like this might not be ideal in the summer due to the heat...  i would suggest anyone with a crappy fuel system to try this setup and see how it goes, but discontinue when the weather warms up.  a small fuel cooler might be a good idea while running like that in the summer though...
  
  i guess the main reason i'm writing this is to say that his cloth lines are holding at least 7 psi pressure and not blowing... i would also suggest some new cloth lines (they won't seal the same ever again as when they did when first put on)
• #3 by autoholic on 27 Dec, 2008 19:30
• Maybe one of the small return ports in one of the injectors is plugged?
  Something is plugged somewhere, there should be vitually no resistance to flow on the return side (other then the orifice in the pump banjo itself, which is upstream).
• #4 by dillenger1 on 28 Dec, 2008 06:16
• ive blown two different lines so i dont think theres a clog ,a restriction ,yes.
  What i dont understand is the cloth lines are similar "id" to the return,even smaller then the return to tank.So why all this pressure.The return does have a bigger nipple off the bango,but thats coming off the same banjo.
  Ive also noticed some surging right off idle.
• #5 by dillenger1 on 07 Jan, 2009 14:59
• bumpity,bump.Im still blowing lines.I enlarged the return to 3/8"od tubing.The return banjo is from a NA motor,is this different?It only blows when i wind it out.I dont know where to begin.
• #6 by theman53 on 07 Jan, 2009 16:06
• "I keep blowing off my cloth lines on hard pulls.Whats up?I thought the return need to be restricted.My feed from tank is 1/4"id stainless tube my return is 1/4"od,so it is quite smaller" end quote
  
  I have a guess. Run a 1/2" return instead of the 1/4" and see if it changes anything. It is worth a shot and then if it isn't that you can start looking elsewhere. But that is what would make sence to me. When you are at the highest RPM it should be pulling the most fuel and when the governor kicks in eventhough it is pulling the fuel in it might be using less of it.
  
  The only time I had trouble was with old cloth lines and when I replaced them with chainsaw fuel line I never had the problem again. Also I took my fuel cap off and blew 120PSI back to the tank until fuel flew out the filler and I knew there wasn't a restriction.
  Like I said I am guessing and throwing it out there.
• #7 by Sprockets on 08 Jan, 2009 04:10
• Ok, this may not be your situation, but heres a little case study for you.  I had an old 90 landrover TDi brought to me because it would start and drive fine, and idle all day long.  Drive it hard and would slowly get slower and slower to the point you would have to rebleed the system to get it running again.  After some mucking about I noticed the tank was getting pressurised, and then it came to me.  The LDA had a split in it, so boost pressure was escaping into the fuel system.  New diaphragm installed, ran superb and never missed a beat
  
  So my advice at the end of all this?  Have a quick look at the LDA, or even take the fuel cap off and see if it still does it.
  
  -Gavin
• #8 by dillenger1 on 08 Jan, 2009 16:06
• thanks will try tommorrow.
• #9 by smutts on 09 Jan, 2009 13:16
• Quote

  After some mucking about I noticed the tank was getting pressurised, and then it came to me. The LDA had a split in it, so boost pressure was escaping into the fuel system. New diaphragm installed, ran superb and never missed a beat Smile

  
  
  That is a sneaky one that is, well found!