How to diagnose fuel problems - Troubleshooting - VWDiesel.net The IDI, TDI, and mTDI source.

• How to diagnose fuel problems by zozie on 06 Jan, 2009 05:56
• Well my mk1 1.6D n/a did it again.
  I know I have a small fuel leak so I think that's what's causing the headache. When the temp dips to about -10, the car will start and run fine, then in 5 minutes it will loose power and die. I use additives and keep my tank full for the most part. I happened before and as I drive it it improves but this morning I just left it alone. It was surprising cause I drove it yesterday and filled it up. (it's my everyday driver with about 120kms/day for work and drinks about 4.8l/100)
  
  Could ice in the fuel be caused by my minor leak on the tank? I'm just wondering because I guess the fuel expands as it warms up, then as it shrinks when I leave it alone it may suck moisture in, which then gets frozen.
  What u think?
• #1 by the caveman on 06 Jan, 2009 07:10
• I would think that if the leak was your problem then it would be between the tank and filter. My thinking is that there is enough fuel in the IP, line between it and the filter and in the filter. If i were you replace the filter. What happens when it is cold is that, again there's enough in the line and pump, but because the filter is old, it has trapped water and is now frozen. So the car starts with what is after it but then runs dry. Also use some WINTER fuel conditioner to slow down waxing.
• #2 by fatmobile on 07 Jan, 2009 00:45
• Do you have clear fuel lines?
  If you do; can you see air bubbles in the fuel?
  
   A vacuum gauge connected to the fuel line will let you know when the pump is working hard to get fuel,.. due to a fuel line restriction.
• #3 by Smokey Eddy on 07 Jan, 2009 01:46
• How often does one change the fuel lines?
  my return line has cracks in it but doesn't seem to be weathered...
  
  Where do the bubbles tend to originate? from a not quite so full filter?
  
  Can that plastic nob on the top (inline of the return) leak air into the filter sending bubles through the feed line?
• #4 by fatmobile on 08 Jan, 2009 00:57
• I like clear lines to and from the pump,
   and change them when they get brittle or unclear.
• #5 by burn_your_money on 08 Jan, 2009 04:54
• It could be your water seperator
• #6 by zozie on 08 Jan, 2009 11:14
• Well I changed the filter and it got cured. There is no water seperator on the tank of the MK1.
• #7 by Tony2ltr on 08 Jan, 2009 17:40
• What is the proper material for the clear fuel lines to and from the IP?
  HOw about for the injector return lines?
  Is there a good source for these?
  -Tony
• #8 by fatmobile on 08 Jan, 2009 23:02
• I like urethane from motorcycle shops.
   Comes in a lovely clear blue,.. and I think other colors.
• #9 by Tony2ltr on 09 Jan, 2009 07:32
• Is this like the yellow stuff that you get for small engine repair, chain saws and the like?
  
  -Tony
• #10 by the caveman on 09 Jan, 2009 07:45
• Quote from: "zozie"

  Well I changed the filter and it got cured. There is no water seperator on the tank of the MK1.

  
  So i guess i was right  
• #11 by Tony2ltr on 09 Jan, 2009 16:43
• I started my rebuilt 1.6 ecodiesel (NA block) for the first time today.  I had a lot of air bubbles in the line, so bad that there was no return fuel, and it eventually died.  I bypassed the water separator, and it helped (the fittings were all very rusty), but there are still a lot of air bubbles in the line!  I wonder if the fittings on the top of the tank are sucking air?
  
  -Tony
• #12 by fatmobile on 09 Jan, 2009 21:29
• Yes I think the chainsaw shops sell urethane fuel line too,... that is not blue. I think the orange stuff at Ace hardware is urethane too.
   
   Check the screen on the fuel pickup in the tank. It might be clogged.
   Have a vacuum cleaner ready to clean up all the crap that accumulates around the sender, before you open the tank.
• #13 by Tony2ltr on 10 Jan, 2009 13:40
• Well, I got it going today.  The stupid fuel filters that they use for that era diesels (with the plastic banjo) was sucking air in. I replaced it with an older style, and just returned the fuel to the tank, and no problem, no more bubbles in the supply hose.  I had some problems getting my air cleaner box hose back on the car because the turbo that I used (early 80's) has a bigger inlet on the compressor. the air cleaner box hose would not go on it anymore, so I had to steal a reducer coupling from the turbo plumbling on my Cosworth Vega. I turned the fuel screw on the IP up about 1/2 turn, and now I have a lot more power,  but the blowoff valve (also from the early 80's engine) is limiting the boost to 15 PSI.
  now the brakes need some work, and I need some new tires(and rims), but I am very excited about the new engine, so far it runs great!
  
  Can I access the pickup in the tank through the hole in the trunk floor?
  
  -Tony
• #14 by Tony2ltr on 10 Jan, 2009 13:40
• Well, I got it going today.  The stupid fuel filters that they use for that era diesels (with the plastic banjo) was sucking air in. I replaced it with an older style, and just returned the fuel to the tank, and no problem, no more bubbles in the supply hose.  I had some problems getting my air cleaner box hose back on the car because the turbo that I used (early 80's) has a bigger inlet on the compressor. the air cleaner box hose would not go on it anymore, so I had to steal a reducer coupling from the turbo plumbling on my Cosworth Vega. I turned the fuel screw on the IP up about 1/2 turn, and now I have a lot more power,  but the blowoff valve (also from the early 80's engine) is limiting the boost to 15 PSI.
  now the brakes need some work, and I need some new tires(and rims), but I am very excited about the new engine, so far it runs great!
  
  Can I access the pickup in the tank through the hole in the trunk floor?
  
  -Tony