Hey guys. I got a pretty loud knock happening with the old Cummins and could use some help identifying it. My alternator went out on a business trip this week. In an attempt to limp the truck to the next town I ran it dead. I had a new alternator put in it and got it all charged back up. 

When I fired it back up it was smoking a lot I had a miss and knocked real bad. I put about 20 miles on it and the miss/smoke went away but the knock is still there. 

It changes up and down with engine speed. I have checked under the hood or tools left over belt issues and anything obvious. Boost fuel pressure and exhaust temp are all normal. 

No check engine light but I will pull codes next time I get a moment. 

Any help would be greatly appreciated!! 

Too much rhythm. It's not random. Metal to Metal tapping. That's why I think valve lash. Not to mention is running too smooth to be a fuel issue.

What about bad fuel? Cetane numbers being out of whack?

Pull the filter and cut it open.... hope to god there aren't any shavings in it.

Which filter

Oil filter I think is what he is getting at

Probably the oil filter. I will pull the valve cover off this weekend just to check things over and check the valve lash. 

If I were to run the engine with the valve cover off what I make a big mess? Maybe I would be able to see something while the engine is running if there is a problem in the valve train. 

Better off just take the time remove the valve cover and inspecting by hand with the engine off. Start at TDC and check your rockers if any are really loose then look deeper. Possible but rare is bent push rod.\

12 hours ago, CSM said:

Oil filter I think is what he is getting at

Correct. I should have been more specific. My bad!

3 hours ago, Ilikeoldfords said:

Probably the oil filter. I will pull the valve cover off this weekend just to check things over and check the valve lash. 

If I were to run the engine with the valve cover off what I make a big mess? Maybe I would be able to see something while the engine is running if there is a problem in the valve train. 

Yes, you can run it with the cover off. The worst thing that will happen is oil running off the back of the head. Not a big deal

On ‎1‎/‎15‎/‎2016 at 8:15 PM, Mopar1973Man said:

Valve lash...

I think running the valves would be a good place to start, sounds like its in the top end.. just my two cents

not to scare ya but i dont think its a fuel issue either.

either a valve issue

wristpin failure

or conrod bearing failing (piston slap), i can hear the bang come after the compression/ignition stroke and it might be slapping the piston onto the head during the exhaust stroke

just my $.02 hope you find the issue and its an easy fix

I can't even think how many times I have seen and heard knocks like that and worse all caused by injector issues. have seen a lot of wasted time labor and parts costs thrown at equipment by misdiagnosed knocks where folks thought it was internal versus fuel related.

 

Start simple and work your way in, do not tear in and work your way out. Crack injector lines then go with an infrared heat gun and hit the exh. manifold ports looking for a cold cyl then go from there.

Remember you are diagnosing a diesel not a gas engine.

Along Wild & Free idea I would pull the injectors out for pop testing and inspection. While they are out you can do compression test verify the engine health. Minimal impact and tear down but gives clues. Also while the valve cover is off you can check valve lash on the valves easy enough.

Typically a bad injector would continue to smoke wouldn't it? (cracked tip or blown tip)

Can't say its and injector yet, they can only do what the IP makes them do, if the IP can't make enough pressure to pop the injector it could be the VP yet causing issues that have not yet fully developed to causing a code or other symptoms. Just need to wait and see where his digging leads us at this point.

Edited January 16, 20169 yr by Wild and Free

like wild and free stated, start on the easy stuff get it out of the way. crack the injector and if the knock goes away it is highly caused by fuel

3 hours ago, Wild and Free said:

Can't say its and injector yet, they can only do what the IP makes them do, if the IP can't make enough pressure to pop the injector it could be the VP yet causing issues that have not yet fully developed to causing a code or other symptoms. Just need to wait and see where his digging leads us at this point.

The only problem there is typically a bad VP44 or PSG would make it random in nature of knock because of failure. But to have a good rhythm. Still that is cylinder based or valve based. Even weak injectors have a random hit / miss type of problem. Not unless the injector is stuck open or horrid pop pressures that way low. Even then would be starting issues from loss of prime. 

Thank you guys for all the leads. I was going to start digging in on it today but it has been snowing all day here and I have come down with a wicked cold. I know, I know I am just being a pansy and need to fight through it

If the weather is better tomorrow and I am not dying I will definitly jump on it. This is the first time my truck has ever been down and even in the last few days I have been feeling it already.

I will post any and all findings ASAP.

Thanks again for all the support. Kind of sucks being the broke down one after all this time.

Ok I have it narrowed down to a cylinder. I went through and loosened up the injector lines one by one and the knock completely went away when I loosened #6. Apart from the dead miss all the extra noise was gone until I tightened the line back up.

On a side note, I just noticed there is a lot more blow by then normal too It is almost enough to lift the oil fill cap all the way out of the hole when just sitting in the valve cover. That is not a good sign.

I would start with swapping another injector in that hole and see if the knock follows. If it doesn't follow, well I think you've got much bigger issues.

UGH!!! and its not a 3rd gen.........

On 1/14/2016 at 9:25 PM, Ilikeoldfords said:

I still have not seen a check engine light yet though and all gauges are working as they should. 

I know!  Nice change from the normal.