Dawg Awful Noise On Start Up After Glow Plug Change - IDI Engine - VWDiesel.net The IDI, TDI, and mTDI source.

• Dawg Awful Noise On Start Up After Glow Plug Change by thomas m on 14 Apr, 2021 16:52
• Rattley, Clackety, Bang, Bang, Oh my, is this the end?
  
  Well,all I did was change the four old (2 bad) for new, Bosch and Beru with attendant fuel line removal.
  Pretty straight forward, so no reason for anything to GO WRONG, right??
  I primed the lines to the injectors by letting a little fuel flow from each before buttoning them up.
  
  The engine was preheated as my glow plugs were not yet hooked up.
  It started right up, a little rough idle and then clackety, bang some pretty harsh noises. Smoke !!
  I let it run and it smoothed out, but then repeated this awful noise several times. Smoke!!
  I revved it and it smoothed out and then ran rough again.
  Finally, after some judicious throttle work it runs smooth.
  
  What on earth caused all of that racket???
  Nothing was removed except what necessary to change the plugs.
  There was fuel in the lines, I guess.
  All plugs drawing about 20 amps each after all of the excitement.
  
  
  
  Comments, please.
  
• #1 by ORCoaster on 14 Apr, 2021 19:44
• Smoke and noise are the symptoms.  Work done was a simple replacement of bad parts.  So what could be wrong? 
  
  The symptoms mimic poor timing.  Either too advanced or retarded gives smoke.  Too advanced gives the noise.  Why would it jump timing?  Should not do that but you did pull the intake line and that may have introduced air into the pump and that might have been the problem. 
  
  Revving it up was the right way to get the air out of the pump.  It may not all be gone either so don't be too surprised if it barks at you a little in the near future. 
  
  Other than that I think you will be OK from now on. 
• #2 by thomas m on 14 Apr, 2021 20:14
• If it jumped timing, it must have jumped back, since it ran fine on a short drive. Probably not the case.
  
  You said:
         

  Quote from: ORCoaster on 14 Apr, 2021 19:44

  
  but you did pull the intake line and that may have introduced air into the pump and that might have been the problem. 
   
  Other than that I think you will be OK from now on. 
  

  
  To which "intake line" are you referring?
  I understand that since I emptied the metal pressure lines, they filled with air and maybe I didn't purge all of it out.
  Did air get into the outlet of the pump when I took the lines off?
  
  I also pulled the rubber lines between injectors and got air in there.
  
  Can you explain?
  
  
• #3 by fatmobile on 14 Apr, 2021 21:31
• Did you pull the injector lines to change the glow plugs?
   Possible you got dirt in an injector.
   Lots of people don't put caps on them when the lines are removed.
• #4 by thomas m on 15 Apr, 2021 07:58
• Fatmobile,
  
  Yes, first thing after removing the lines I put tight fitting plastic caps on all pump outlets and injectors.
  
  Before assembly, I wiped the lines clean and blew them out with shop air.
  
  After a  short drive around the neighborhood, the engine seems to be running well.
• #5 by fatmobile on 15 Apr, 2021 19:58
•  So you did remove the injector lines.
   Glad to hear you covered them quickly.
  
   I got a small spec in an injector once and heard the knock knock.
   It's scary.
• #6 by ORCoaster on 15 Apr, 2021 21:56
• Sorry thought I read where you pulled the line off the IP that goes to the filter.  You did not so air could have come in from the lack of injector lines but NOT likely. There are check valves on the head.
  
• #7 by thomas m on 16 Apr, 2021 12:14
• When I attempted to purge any air in the metal lines, I only let it seep a little at each nut. So, I don't
  think I let all of the air out. There for all of the racket. I saw a guy on a Youtube video have the fuel
  squirt out about 10 inches, so my piddle definitely was not enough to get all of the air out. Better
  to waste a little fuel than have that awful noise. Man, I thought that was the end.
• #8 by fatmobile on 16 Apr, 2021 19:02
•  Air in the metal lines won't make it knock.
   That's a small piece of,
   in my case paint.
  Someone painted the injector lines and a fleck fell into the injector when I removed the line.
• #9 by rabbitman on 22 Apr, 2021 09:05
• Whenever I have the hard lines off I only bleed 2 of them after reinstalling and it starts well enough to self bleed the other 2. It runs rough on startup but never knocks like you describe.
  
  I've had injectors stick at random times and it is a horrendous noise, like what you describe.