Author Topic: Strange Knocking Phenomenon - causes?  (Read 1669 times)

July 04, 2017, 02:48:33 pm


  • Newbie

  • Offline
  • *

  • 2
Strange Knocking Phenomenon - causes?
« on: July 04, 2017, 02:48:33 pm »
Hey, new user here. I have a 1982 (mk1) Diesel 1.6 n/a, and something super strange happened yesterday. My engine had been gradually developing a noise, a sort of slight knock, and I was keeping my eye on it. However I was sitting idle in a drive thru and all of a sudden the engine jerked and started knocking SUPER loud and shuttering like I had broken a rod or something, I thought for sure I'd blown the engine. I should have shut it down, I know, but I was SURE the engine was kaput anyhow and I wasn't far from home so I thought 'screw it, ill ease it back home'. However, after about 30 seconds of this horrible knocking I felt it just 'release' and the knocking immediately ceased, and the car began running PERFECT. Smoother than ever, all 4 cylinders firing properly like nothing ever happened. I expected the problem to come back but all day today it's been running flawlessly.

Given the intense nature of the knock, yet it's temporary presence, I don't know what to think of it. Obviously my rods/bearings are fine because all day today there has been zero problems or any strange noises. Is there something else in the bottom end that could have interfered with the crank spinning (i.e. an oil pickup tube or something), or is it possible that my injection pump shut off two injectors for a moment and the knocking was the engine smacking something from the vibration? I've typically been an aircooled guy and I don't know enough about the bottom ends of these engines yet.

I have limited time to work on the car so I'm trying to brainstorm the most likely causes so I can more effectively troubleshoot when I dive into it. Has anybody had anything like this happen? What's the most likely culprit?

Reply #1July 04, 2017, 04:03:41 pm


  • Administrator
  • Veteran

  • Offline
  • *****

  • 2831
  • Personal Text
    Vancouver, BC
Re: Strange Knocking Phenomenon - causes?
« Reply #1 on: July 04, 2017, 04:03:41 pm »
Very good chance it was injector related. They can cause some pretty brutal sounds when they malfunction. If it stays gone you could surmise that it was a particle of something causing the injector to hang open which eventually cleared itself.

Sent from my LG-H873 using Tapatalk


1994 Jetta - AHU M-TDI - Jezebel Jetta
2004 Jetta Wagon - 1.8T - Blitzen

Reply #2July 04, 2017, 08:26:27 pm


  • Newbie

  • Offline
  • *

  • 2
Re: Strange Knocking Phenomenon - causes?
« Reply #2 on: July 04, 2017, 08:26:27 pm »
Wow. This is my first Diesel engine and I guess I just didn't think that injection failure could cause such a ruckus. This does seem to make more sense than a mechanical failure given the disappearance, though.

Thanks for the response.

Reply #3July 04, 2017, 08:46:42 pm

air-cooled or diesel

  • Guest
Re: Strange Knocking Phenomenon - causes?
« Reply #3 on: July 04, 2017, 08:46:42 pm »
there's no real way to know, looking at the outside of engine, guessing. being its your 1st diesel, and that is a serious knock. 1 change air filter, change fuel filter as well. the fuel filter i get a (small) length of fuel line, and a small funnel, prime filter from inlet, it will help on restart a lot. next i get diesel purge and in a full tank use the whole bottle. can help clear up fuel system. does oil need changing? if so i get an engine-oil flush, and use correctly, on a hot just driven engine, put flush bottle in, and run @idle(&hi-idle) for about 20minutes, change oil/filter. can part way prime oil filter as well.
as far as the knocking, hope van-guy is correct, cause its possible something had come apart, no real way to know looking at the outside of motor, tho,. could be you have a problem, and it could have gone 'silent' doing something you dont want in there.
another way is to bottle feed a whole bottle of the purge straight into pump, and run return line into can.