My guess is old fuel filter... your thoughts? - Troubleshooting - VWDiesel.net The IDI, TDI, and mTDI source.

• My guess is old fuel filter... your thoughts? by Smokey Eddy on 03 Jan, 2011 16:22
• My aaz starts just great most of the time. But when it's left for too long it will start up just fine, idle for about 2-3 seconds and slowly chug out like its ran out of fuel. - by slowly i mean less than 5 seconds... but its not an abrupt stop. I think this is a continuation of another problem i've been dealing with.
  When its cold out, i can't just leave... i have to wait at least a minute before i can touch the soot pedal otherwise it will just die and give the same following symptoms:
  
  I turn the key and the engine turns over like the cylinder head isn't even there. no diesel comes out the exhaust which leads me to believe that the pump can't suck fuel through the filter.
  
  The filter was replaced oh... uhm... around 80,000km ago?
  My brainz tells me to replace the fuel filter. OR is this something only a lift pump will solve?
  The injection pump is an original from a 1990 1.6td.
• #1 by 8v-of-fury on 03 Jan, 2011 16:42
• The timing belt could have been over tightened at some point in the last 21 years, thus ruining the bearing around the pump shaft? Causing it to suck air when sitting?
  
  How does it run when its already going good? Good power? Good mileage? No visible leaks? Any air bubbles returning to the tank? What temp is it there? Fuel Gelling?
  
  20 questions anyone? lol
• #2 by Smokey Eddy on 03 Jan, 2011 17:01
• 1. Runs great once its going
  2. Heaps of power (i think)
  3. Mileage was sucking terribly due to a leaking injector but JB weld fixed it. Back to about 45mpg.
  4. no more leaks
  5. no bubbles coming from the filter (through a clear VINYL line) and my return line is very old, cracked and stiff and not clear...
  6. it is currently +3 from a low earlier this morning of -6
  7. dont think gelling is an issue since its never below -10 here..
• #3 by Doug on 03 Jan, 2011 18:03
• My diesel land cruiser behaved the same way but under cold conditions (-25C). Some filter media will stop flowing when contaminated with water. It took two filter changes as well as a full container of conditioner to get things moving again properly. I have had gas engined vehicles do the same with the culprit being a plug of ice in the lowest part of the fuel line. Had to use the heat gun on the fuel line to get things moving, with lots of alcohol in the tank.
  
  The easiest thing is to replace a filter. I would start there before your imagination gets the better of you.
• #4 by 8v-of-fury on 03 Jan, 2011 22:43
• yeah plus its a cheap and easy fix.
  
  Filter change, filled with diesel conditioner upon install. See what happens lol
• #5 by Smokey Eddy on 12 Jan, 2011 04:32
• I changed the fuel filter to no avail.
  I did notice however that when i pulled my clear line off the filter (the line that goes to the pump) the diesel travelled down into the pump... as if it was under vacuum and there was a pocket of air inside the pump that the diesel then took the place of...
  
  didnt seem to make sense to me and it gave me hope that changing the filter would solve the issue but it most certainly has not.
  
  To be more descriptive:
  
  after sitting for over 10 hours, i let the GP's run really hot for about 15 seconds, turn the key, it starts very quickly.. first or second compression stroke. starts ... fantastic.
  
  idles fine for about 1-2 seconds then putts to a dead halt in another 1-2 seconds.
  
  I usually swear really loudly inside the car at this point and turn the key again only to find it seemingly has no fuel what so ever.
  
  I plug in the block heater for 45 minutes - no dice.
  over and hour - starts fine.
  
  its only -2C (28.4F) ... and thats the low for the day ...
• #6 by Smokey Eddy on 12 Jan, 2011 04:33
• I also did an ear test of the stop solenoid and i can hear it clicking quietly when i tap it on and off with a spare length of wire to the battery.
  Using a huge battery with fully synthetic 5w-40 Moly Lubro. stock 1.6td injectors modded 1.6td pump (but haven't touched the pump its self in a very long time so its not a recent change to the pump to be at fault)
• #7 by Doug on 12 Jan, 2011 08:24
• I have seen the fuel solenoid partially stick open/closed to give similar start/run/peter out operation. It is easy to pull the solenoid to check operation as well as clean the bore it slides in. Hypothesis-fuel solenoid sticking only partly open while cold on first start or before full block heater warm up. Maybe the additional heat to the unit or vibration allows it to slide easier? Maybe there is some corrosion on the plunger. You could replace it with a new one or one that you know has full service operation to eliminate this possibility.
  
  Are you absolutely sure that the supply wire to the solenoid is not broken inside the plastic insulation jacket giving momentary contact under some conditions? Again first hand experience has taken me there.
  
  Get rid of the sedimenter assembly by the rear axle. The plastic seams on the unit will leak allowing air into the system giving similar operation. When it gets really bad your pump will not be able to prime itself.
• #8 by Quantum TD on 12 Jan, 2011 12:28
• It sounds like your tank is not venting properly. I'd replace that return line, and blow it back to the tank. I'd also try to pull fuel from the tank with a vacuum pump. I'd do it before removing the gas cap, and then after. It should pull the same in both instances if the tank is venting properly. I'm not sure how the venting works on MK3 cars, but there may be a gravity valve that's stuck.
  
  Regarding the return line. The one on my Rabbit had been weeping for some time. My mileage sucks (like 36 MPG in the winter). The last 2 winters, I've had to replace the fuel filter on the highway after only 10,000 miles. They would freeze up and start sucking air. Both times, it was ***ty Exxon fuel that was the immediate culprit, but I could never explain how the pump could suck air from the tank. I'm starting to think that it was actually sucking air into the pump from the return hose.
  
  Just yesterday, I tried to start my truck in 15F degrees weather. The truck has never had a problem starting in those temps, though it will chug a bit on startup. Well, it wouldn't start. So, I shot some starting fluid in there (BAAAD IDEA). The battery shorted out and did not crank at all. So, I had to pull the injectors to blow out the ether. Then I checked the plugs while they were out: all glowed great. When I had the injectors out, I pulled the OUT bolt off the injection pump. I noticed that the fuel in the pump looked low. So, I ended up putting about 1 cup of fuel in it to top it off. It's not leaking, so the only explanations are that it was not pulling fuel from the tank due to gelling (not cold enough for that, and I run an additive), or it was sucking air into the pump (likely thru the return hose). It also turns out that one of the return nipples on my #1 injector was broken and hanging on by a thread. I had to replace the body on that one injector.
  
  After all that, and 3 glow cycles, it fired right up.
  
  Bottom line: If you have air leaking in (usually indicated by fuel leaking out), fix that. But in your case, it sounds like you're not properly pulling fuel from the tank, either due to a blockage or improper venting.
• #9 by Smokey Eddy on 12 Jan, 2011 15:15
• Wow thanks for the input. There definitely isn't diesel leaking anywhere but i know the lines to and from the tank arevlikmoely original.
  Ps. I removed the water and sediment seperator already.
• #10 by Smokey Eddy on 14 Jan, 2011 16:43
• Okay so i think i know what the issue is finally.
  It's been illusive because its not quite easy to see the problem.
  
  It's not actually a temperature thing but a time issue.
  I have a clear line going from the filter to the pump and it has a protective sleeve over it that i pull away to check for air.
  While the car is running its clear and good, maybe the odd bubble.
  but after the car has been running a very small amount of air gets into the line at the pump it's self. at first glance i can't notice the tiny bubbles but over several hours they must accumulate into something more troublesome. I'm going to replace the line and put some good clamps on the two barbs and that should solve the issue.
• #11 by 8v-of-fury on 19 Jan, 2011 13:25
• I find that having your pump as being the lowest part of the fuel system under the hood really helps with any sort of drainback. If the lines that leave the pump go above it, if any air ever gets in it doesn't drain the pump..
• #12 by Quantum TD on 19 Jan, 2011 23:19
• Don't rule out return lines (between injectors, and back to the tank) as a possible source of air. The idle on my car would hang all the time. I rebuilt the injectors, resealed the pump, etc. Turns out the main return hose was old as crap, and weeping when running, and sucking air too. Since I've replaced it, starts are better and the idle doesn't hang anymore.