wierd cold start problem - page 1 - General - VWDiesel.net The IDI, TDI, and mTDI source.

• wierd cold start problem by wadem on 23 Nov, 2012 09:18
• Hi guys, am having trouble with my 96 AAZ Jetta and its making me tear my hair out! whenever the temps get to -7 degrees C or colder my car is not driveable due to the following:
  
          Last year i "pimped my glow plugs" thanks Vince, and the car has been starting great even at -20 degree temps.
          The problem popped up last year but only when it was really cold so it wasnt a big issue.
  
          - car starts initially after plug warming no problem. then after idling for about 1 minute it starts running rough and loses rpm then dies. Its like its running out of fuel and no amount of playing with the throttle helps. If you try and restart the engine, after turning the starter over for an eternity sometimes if fires up again and will run normally and other times it will just run again for a minute or so then die. This is destroying my battery and starter! Here are some observations: while looking at the clear fuel lines while it is running and just before it dies, the smaller return to tank line is full of air bubbles,so many that it looks like foam! The larger fuel feed line from the filter seems clear and full of fuel. when and if you are lucky enough to get the car started again both lines are running nice and clear...again it is if the car is fuel starved but it looks like the feed line is full. Like i said this happened last year so I pulled the fuel lines and cleaned them out. I found a bunch of contaminents right before the one way check valve right after the tank. Looked like bits of silicon and plastic, maybe from a previous repair or from new. The check valve was also bad, so i cut out the valve and ran with just the line itself. The car ran great like this for the rest of the winter last year and up until now, i thought i had found the problem.
     So yesterday I repeated the process and cleaned out all the lines, changed out the filter, checked for leaks and also vacuum tested all the lines to assure they were air tight. Drove the car last night for 50km and it ran like a top. This morning I tried starting it -7 degrees c out, and it did the same thing!!! Starts right up runs fine for 45 seconds, then runs rough and dies, turn the starter over for a million seconds and it clears and starts, but then did the same thing after a second run of about 1 minute. Again, return line full of air bubbles......WHAT COULD THIS BE!!!!!
     The car has about 340.000km's on it and when its warm it starts great. Even when this problem happens, after several cycles of it dying and starting it seems to fix itself then runs fine for the rest of the day.
     Is it possible that air is somehow getting into the pump and its aggrevated when cold outside? why would it fis itself after several starting attempts? When you run out of fuel do you get airbubbles in the return line? Even so, it seems like the main fuel line is full.
  Could the IP itself be failing and doesnt have enough suction to feed the injectors when its cold? I have also tried conditioner but it also didnt help.
    Any ideas here would be greatly appreciated!
  
  Cheers
  
  Wade
• #1 by TylerDurden on 23 Nov, 2012 09:35
• Air in the IP looks like foam in the return line.
  
  I would first try bottle feeding it when cold - lines in and out of the IP to a container with fuel. If that works well, your lines to the tank/filter have a problem.
  
  If you still have the problem while bottle-feeding, it may be the front seal is bad and the cooler temp is enough to stiffen the seal.
  
  An interesting test might be to warm the IP pulley, shaft & seal with a hair dryer to see if the problem resolves.
• #2 by 8v-of-fury on 23 Nov, 2012 09:51
• Tyler, I agree with your post entirely.
  
  Bottle feeding it would be the first step I would take. With those results we can give you a much better diagnoses. However it definitely seems like the pumps front seal has gone bad. With no air in the feed line the air can only be really coming from two more seals on the suction end of things. The governor shaft has an o-ring and it is on the suction side of the pump, its replacement will need half of the fuel pump to come apart. The other seal on the suction side is the main shaft seal, and it may or may not be able to be done on the car. In fact, I have never tried replacing one that I didn't already have the pump completely torn down.. I imagine it would be a real PITA to do..
• #3 by TylerDurden on 23 Nov, 2012 10:03
• I've heard of people changing the mainshaft seal while the IP is in the car, but I haven't tried it that way myself. Other seals are usually going bad anyway.
  
  FWIW, I'm not sure the governor shaft is always on the suction-side, the one I just replaced on a 107AD was pushing out fuel when the pump was running.
• #4 by burn_your_money on 23 Nov, 2012 11:38
• Pop the timing cover off and see if the belt is wet, especially around the pump shaft.
• #5 by wadem on 23 Nov, 2012 13:51
• I'm pretty sure the problem is with the  pump as well. But I will pursue the other ideas mentioned as well.
    So how difficult is it to re-seal a pump? Can you just put new seals in and go or should you rebuild the pump as well?
    Is there any info or threads on this in the forum or online?
    And finally, where can I get these seals from?
  
  Wade
• #6 by TylerDurden on 23 Nov, 2012 15:17
• The main seal is not that difficult if you have above average shade-tree mechanic skills & tools. The cold-start lever is also fairly manageable (out of the car). The rest are rather fiddly and some parts require precise replacement. All injection/fuel work requires very clean handling.
  
  There are differences between pumps, but a general idea can be gleaned from this teardown: http://www.vwdiesel.net/forum/index.php?topic=4353.0
  
  Seal-kits and the main seal (sold separately) can be obtained online or from you local fuel-injection/diesel/turbo parts & service shops.
  
  Some of the members provide the reseal service for a fee.
  
  Post pics of your engine, IP and the numbers on the pump... more members may chime in with more info.
• #7 by wadem on 23 Nov, 2012 16:08
• Thanks again for the info, heres a bit of an update:
    It warmed up today so the car started fine and kept running. I drove it for about 20 minutes and when I got back popped the hood and was presented with a steam like vapor trail coming from behind the pump and a very strong smell of raw diesel fuel. During the past few weeks I have been noticing a strong odour of fuel coming into the car, especially with the heater and fan on. Turns out that the  back of the IP is soaked in fuel right around the spot where the cold start lever/cam are. I restarted the engine and revved it up and with a flashlight was able to see a very fine but powerful mist of fuel spraying from the pump.....NOT GOOD!! So i'm thinking that this could be my issue when starting when its cold, somehow it is aggrevated with the cooler temps and I must be getting air into the IP.
    So at any rate it looks like I'm going to have to do some shopping, and decide if I want to do this or not. Kind of a shame as i just did the timing belt a few months back and had it all torn apart.
     Who are the guys that will reseal the pump?
  
  Wade
• #8 by TylerDurden on 23 Nov, 2012 16:46
• You might post your location or add it to your profile... there could be a member in your area, so you wouldn't need to drain & ship.
  
  If you decide to DIY it, lotta help online here. Seal kits are ~$15 (turbo adds $4), the main seal is ~$15 also.
  
  To reduce downtime (& because I'm lazy), I do the CS shaft & CS cover, the main seal,  the governor shaft and big o-ring. Those are easiest to do on the bench... if the others start seeping later, I can do them while the IP is in the car.
• #9 by ORCoaster on 23 Nov, 2012 20:08
• Seal kits on line listed by number elsewhere in the forum.  Sounds like you only need to pull the pump off get that Cold start lever cover off and throw in a new O ring.  you might even be able to get it out of there and run to the auto store or hydraulics shop and pick up one for less than the kit and be done in short order. 
• #10 by wadem on 24 Nov, 2012 07:27
• Again, great stuff and thanks for all the tips. I will try and pull the pump in the next few days. Not sure if I will repair it myself or have it done! How difficult is this to do yourself? I am pretty comfy around a wrench, have rebuilt several engines and have just done the timing belt. But am a little freaked out when I look at all the parts in a IP.
    What is the best fastest or easiest way to pull the pump off the car? Do you always have to re time the pump with the dial gauge after its removed? or can you just scribe accurate marks on the pump body? To me the timing belt was a big job and if possible would like to make removing the pump not so big.....advice?
  
  Wade
• #11 by bbob203 on 24 Nov, 2012 07:45
• Just for good measure set the engine at the timig marks and use alligator clips to hold the belt on the cam pulley and the Intermediate shaft and put a few markings on the pulley and belt of the ip to get it all lined back up. As long as it doesn't move or come off the crank your good.
• #12 by ORCoaster on 24 Nov, 2012 10:05
• There is a sticky on this forum about rebuilding the IP.  Not a hard thing to do but there are parts that don't come off easy without special tools.  Tools that can be made or worked around if you want to.  In order to tear it apart deep down you have to get the governor assembly and control lever off the unit.  Those 3 sided nuts can be a bugger.  Mostly it is a stand it on its nose and take apart from the top down.  Turning it on it's long edge will have things tumbling out in short order and have you saying Holy Crap in about the same amount of time.  Lots of pictures of exploded views on here as well.  Again check the stickys. 
  
  A clean environment is needed along with a good 25 torex bit if I remember it right.  Those nuts on the back end and the fuel shut off are a tight bunch on all the pumps I have broken into. 
  
  Good reading and good luck.  DAS
• #13 by R.O.R-2.0 on 27 Nov, 2012 11:07
• have you checked your fuel filter?
  
  a plugged up filter will do this same thing..
• #14 by wadem on 27 Nov, 2012 20:54
• Yes, I have checked the filter, and i replaced it just to be sure.
    There are a few things that dont make sense to me though. If the seals or seal is leaking all the time, why doesnt the car not start all the time? this issue only crops up when its really cold, or colder anyway, around - 10 degrees c or colder. Like i said before, the leak on the pump seems to be coming from around the cold start lever or cam, and its always leaking a pretty substantial drip, hot or cold outside.
    Also, what are you fixing or clearing up with the pump when you turn it over to the point of almost killing your battery and then suddenly it starts fine and keeps running. Theres no doubt that the seal around the cold start has to be repaired, but could this be whats causing my problem when starting? If the fuel is coming out of a bad o-ring or seal, when would it be able to suck air in to cause the air bubbles in the return line?
    After the car decides to keep running it works and runs like a clock, and eventually the return line purges itself of the air bubbles, again an explanation? This morning it was around - 8 degrees celsius and the car started fine and kept running. Right after it started I popped the hood and watched the same mass of air bubbles coming from the return line. I fully expected the car to start idling rough and die but it DIDN'T! Ran like a clock. I revved it up a few times and kept it idling and the bubbles never cleared up. I decided to take it for a drive down the highway for 10 minutes and by the time I got back the bubbles were gone and the line was clear.........Again I dont understand. The leak must be fixed, I agree, but im starting to think that thats not going to solve my starting issue.........comments!
  
  Cheers
  
  Wade