hollow thump on cold start

[fuelscrew]

So on a cold start now there is this hollow thumping sound dose it five or six times in time with the motor then goes away. Kinda sounds like placing your flat palm over one end of a piece of exhaust pipe if that makes any sense.no unusual smoke white with some black then none like it always has. Any ideas?

 

[Greenie]

Mine has done that for years - sounds awful but it quickly comes out of it.

 

[Dave Barbieri]

A hollow thump is usually a cylinder not firing. Magnify the sound and increase the frequency and that's what a Jake Brake sounds like at operating speeds. Might be a valve not fully seating at first, might be a balky injector. My truck did that for a while, then it got to the point that the noise didn't go away. It was louder if I removed the air cleaner. An intake valve wasn't seating. Since there's over 300k on the engine, I'm rebuilding instead of just doing a valve job.

 

[ford 6.9]

Mine does this also. It does it until all the cylinders light with fuel. Lasts a few secs.

 

[IDIDieselJohn]

My van also does this. Very loud thumping sound, more noticeable with the hood open.


Does it the loudest when cold, quiets down as it warms up, but does it for a good while before going away....and sometimes comes back.




On the way home with it when I bought it, a 2 hour highway drive, at a random time, about half way home, it started doing it, extremely loud, and she was screamin over 3k RPM at 60mph, did it for a few minutes, and thankfully went away, it was so loud, it made my ears ring after!


I'm thinking it's a bad injector, as it does have a missfire when it's cold. Only has 92k miles on it.

 

[fuelscrew]

Thanks everyone I'm thinking bad injector it didn't start doing this till I changed them for a rebuilt set I got on the cheap it runs 10 times better than with the old set maybe ill yank these and get them tested at antrim Diesel