Weird pump problem, loosing prime, pushing foam out the inlet when shut off..etc - Troubleshooting - VWDiesel.net The IDI, TDI, and mTDI source.

• Weird pump problem, loosing prime, pushing foam out the inlet when shut off..etc by vwjunkie53 on 04 Apr, 2010 18:38
• I'm having a weird problem with the injection pump.  We bought the car not running and had a hell of a time getting the engine to start.  Came to find that from sitting so long the fuel pump was totally dry.  I got it primed, but it would only stay running if reved up and once it started to idle for a couple minutes, it would slowly start to loose rpms and not respond to throttle imput.  When it would die or you shut it off, a big burst of foam would come blasting back out from the pump inlet??  We ended up getting a good injection pump on the engine, but a few weeks later blew the head gasket.  After just rebuilding the head and installing a new gasket, the pump that was working is now doing the same thing the old one did...  It looses prime after you shut it off, and blows foam back out the inlet and wont restart like the pump is full of air.  It doesn't leak any fuel out of the shaft seal or anywhere else, jumper lines are all new.  What I don't get is that this pump was working a couple weeks ago!  It sat on the bench and now suddenly doens't work.  I have a clear hose between the filter and the pump, there are no air bubles going in the pump from the fuel system.  Has anyone ran into a problem like this before?  Its obviously an air problem but if that much air is getting in, why isn't any fuel comming out?  Any suggestions would be great.
  
  Thanks,
  Jason
• #1 by burn_your_money on 04 Apr, 2010 19:02
• Run it off a Jerry can (feed and return) and see how it fairs. Next I would hook up the return to the car and see what it does. Then pending the results put the return back in the Jerry can and hook the feed up to the car and see what happens.
  
  Before you do any of that try opening the gas tank cap and see how it runs.
• #2 by 745 turbogreasel on 04 Apr, 2010 19:06
• Try cleaning the pump out screen in the banjo bolt, although if it is blocked, it is probably blocked with pump debris
• #3 by vwjunkie53 on 04 Apr, 2010 19:21
• I don't think there is a fuel inlet restriction, the car has been running for a few weeks with no problem, and had filled the tank up a few times.  The fuel filter is also new.  I will check the pump inlet for crap, but if it was that blocked up you wouldn't think it would be able to blow back so much foam when its shut off.  As I said the old pump did the same thing, but when we swapped on the good used pump I got the problem was instantly fixed and it ran/started like normal untill we blew the HG.
  
  Jason
• #4 by vwjunkie53 on 04 Apr, 2010 19:24
• I will try running it off a seperate can though and see what happens.  Its also having trouble pumping to all the cylinders, it wont fire on #6 it just foams when you crack the pipe, yet the rest of the cylinders are firing fine?  I'm pretty familiar with the VE pumps, but given the design of the head and rotor I don't see how thats even possible...
  
  Jason
• #5 by 745 turbogreasel on 04 Apr, 2010 19:29
• OUTLET  fitting.
  
  rust in a delivery valve may cause a drop in line pressure in that cyl.
  
• #6 by vwjunkie53 on 04 Apr, 2010 19:34
• Oh yup didn't read your post close enough there... I'll check the outlet fitting screen and bleed off hole.  What relation do you think that would have with the blowing foam back out the inlet and loosing prime?  I don't really see how it can possibly do that either, since the vein pump is right there.  I'm talking enough foam to pretty much empty the line from the pump to the filter.  I'll also check the delivery valve, but I haven't come across any rust or junk in the pump or lines when it was apart.  Everything was clean and as I said running fine...
  
  Jason
• #7 by Rabbit on Roids on 05 Apr, 2010 08:08
• check the inlet fitting on the fuel filter ive had a mysterious fuel gremlin live there before. you have a feed line restriction somewhere. or a clogged tank. sounds like to me atleast. my rabbit would do the same thing with a clogged tank.
• #8 by vwjunkie53 on 05 Apr, 2010 10:25
• I think I figured out the problem... The old pump did the same thing, and now that this pump starting doing it out of the blue made me start thinking about the engine itself and other things that could possibly fill it with air.  I couldn't see how the pump could be getting that much air without leaking fuel.  It also has a dead cylinder.  Upon making a call to the local diesel pump shop, the owner made an interesting suggestion.  A bad injector... He has seen it before, and the symtoms make total sense.  A nozzle has hung open, and compression gasses are being pushed back into the pump and are filling it with air.  The injectors we just installed are not the same ones, they have been rebuilt, but who knows something could have gotten stuck in a nozzle and made it hang open.  That would also explain why the cylinder thats dead has a bunch of foam in the line when you crack it.  I'm going to swap in a good used injector tonight and see what happens.  I'll report back when I get it running.
  
  Jason
• #9 by Rabbit on Roids on 05 Apr, 2010 12:00
• but the delivery valve would not let anything back into the pump. it doesnt work that way. unless your delivery valves are both bad on that particular cylinder. delivery valves are small one way valves that the fuel lines thread onto. hook a vacuum gauge up to the inlet side of the fuel pump, my bet is that you will see a fairly high vacuum, where as you should see as close to zero as possible.
• #10 by smutts on 05 Apr, 2010 12:28
•  That foam running backwards is either pressure in the pump, or vacuum in the filter. You might have two things going on at the same time, a hung injector would give the foam when you crack the high pressure line line to it, possibly a dead cylinder too. (But I can't see that gas getting all the way into the pump case.) Also the filter is likely blocked. Happy hunting for the gremlin.
• #11 by vwjunkie53 on 07 Apr, 2010 06:08
• Turns out the owner of thel local pump shop was right (he's been doing it for 40+ years so I checked his suggestion first).  The #6 injector had a piece of crap stuck in the nozzle and compression gasses were pushing back into the pump.  Even with the delivery valve, it still filled the pump with air enough to make it push foam back out the inlet when it was shut off and loose its prime.  We swapped out that injector and its running fine, and starting up without loosing prime.
  
  Thanks everyone for the help and suggestions.
  
  
  Jason
• #12 by burn_your_money on 07 Apr, 2010 10:07
• Thanks for posting the results. I'll have to add that to the mental list of things to check.
  
• #13 by Rabbit on Roids on 07 Apr, 2010 10:27
• yea, me too. i thought the DV would have kept it all out of the pump.