Buzz test only test the electronic side and poppet value. It won't replicate a knock

 

My truck sounds the same. I did UVCH's and no change. I ordered new injectors and will be installing them this weekend. I'll let you know what I find. I was never told it could be low fuel pressure... Hopefully I didn't get new injectors for nothing! I also did my glow plugs for ****s and giggles since I was in there.

 

Like he said, with a buzz test I can't make the knock rear its head. Only when running.

 

Check the heat on each cylinder exhaust manifold and see what one is cold. that should tell you what injector is bad. I had this on number 8 replaced it and all was good. You mitt even find bad o-rings on that cylinder when you pull it. Anyway it's a starting point. It just has to be colder then the rest.

 

I can second this! I am replacing injectors this weekend due to it.

 

I tried this and was unable to find the culprit... They were all burning about the same.

 

Mine sounds exactly the same - gets quieter when is warms up, I'm not going to worry about it

 

Did you check it when it was cold? As it warms up one will stay much colder then the rest usually, then warm up as you drive it. I had a different problem, It was fine when cold but after I drove it and it idled you could here it badly. Specially between walls. Driving it, it sounded normal.

 

Makes me think you may have had a problem with oil pressure or fuel pressure that changed? During driving I would think all of that would be at its best and worst when warm and idling.

 

Yes it was stone cold. Had been sitting overnight if I remember right. Watched all 8 cylinders warm from 70* F I believe.. Might be wrong though.

 

I would check fuel psi and if good then pull the valve covers to makes sure all injector all are seated and tight

 

I assume this was on a super duty ?
The obs typically doesn't have the #8 issue since the fuel system isn't dead headed.

 

Yes, it was a super duty.

 

Ok, now that I replaced my rear main seal and DMF I can move on to this knock problem. First thing first is a fuel pressure test. Fuel filter is new. I haven't tried cleaning the screen though. Does this pressure seem normal to ya'll? It sure bounces a lot!

 

It looks fine to me, or at least where I can see the needle "bottom" consistently on stroke. The bouncing is due to the fact the pump is mechanical and running off the cam lobe. A liquid filled gauge with help with the needle bounce...

It looks fine to me.