https://youtu.be/CXTbl_N14sc

You can barely hear the knocking in the video - for some reason it sounds like a quiet clicking sound on the recording. I can hear the knocking all the way across the parking lot though.

it only does it at idle - the slightest amount of throttle and it goes away. The harder the engine worked, the louder the knocking sound. The big hill headed south from Duluth causes it to chatter and clatter and bang away as soon as the engine goes back to idle, but sometimes it's so quiet I can barely hear it (and sometimes, it's gone). It's really confusing.

 

I read through my 2000 250 yesterday and it says that if you don't use the ford brand oil, motorcraft I believe, that it may cause knocking. Although mine is a gas burner not a diesel. Hope this helps

 

 

 

So last night, I pulled into a gas station next to an old Ram 3500 Cummins. I couldn't even HEAR my '99 F350 over his engine idling...his sounded like someone was literally under the hood with a ball-peen hammer hitting a metal pole so maybe mine is normal

 

These trucks have a personality so if it's just a tick it just might be the nature of the beast. If you climb under at idle and it's louder (more noticeable) there is the possibility that an injector might be loose.

How many miles do you have? When I have gotten a noticeable knock I check the torque on my lower injector hold-down bolts, tighten them up, and that usually solves my problem. There are plenty of threads in the 1999-2003 7.3L section as well as lots of knowledgeable people that can help.

You can search for "hot torque" and see some of the more recent discussions/effect of that. To start you off here's the last one I started a couple of years ago: https://www.ford-trucks.com/forums/8...ing-sound.html

If it's earlier than a '98 that's a mechanical 12-vavle 5.9. Very loud (and sexy ).

The newer the engine the quieter they get, especially for the common rails. My dad's '06 Duramax is a kitten compared to my ferrule cat on crack.

 

Think replacing the fuel filter might help?

 

Got a new filter. Here it is side by side with the old filter for comparison - the old one was beyond gross. Both are the same NAPA filter. It still has the knock but it's significantly quieter, and the idle is much smoother.



Here's the knock, in a much longer video - its mostly noticeable at the wheel wells. It is quieter than it was before I changed the filter.
Edit: That's not a leak on the passenger side frame rail, it's fuel that dumped from the fuel/water separator while changing the filter.

 

The last time mine started knocking like that I tightened the lower hold-down bolts and things quieted down (all of them were loose).

Is that oil on the filter?

Random fatalist theory: Loose injector (knocking) that has damaged an o-ring allowing HPO into the fuel system.

 

It's technically 2-D Fuel Oil (Clear, ULSD) so I guess it's oil It's just horrifically dirty - if you zoom in you can actually see algae on the filter, which would be "biomass" that has separated from biodiesel. It happens nearly every winter with biodiesel, and the truck was originally registered in Minnesota which decided that B10 to B20 would be an awesome requirement for all fuel sold in the state in the summer, and even required B5 biodiesel in the winter (It DID NOT work well when they first implemented it, we had truck after truck with clogged up fuel filters - it was so bad that the company I work for stopped buying fuel in the entire state during the winter months). Supposedly, Minnesota has worked out the B5 winter biodiesel performance problem, and they even made a website swearing up and down that it was never a problem, but they're full of you know what

I have no problem with biodiesel in the summer months, it helps replace the lubricity lost when LSD switched to ULSD, but in the winter months in a state which has seen temperatures below 50 below zero in the winter, you have to use some common sense.

The bowl was clean and didn't show a single trace of dirty oil on it, there is some minor seepage around the EBPV rod but nothing unexpected after 20 years of using a piston.

When you say "Lower Hold Downs" are you referring to motor mounts? Something is definitely loose down there.

 

The injector lower hold-down bolts. They are under the valve covers and are what provide the clamping force to hold the injector in the hole. If they are not tight then the injector can move around (jump) in the hold making a knocking sound.

Here's a picture of where they are:



There's plenty of chatter on this if you search but the link I put in post #6 has the info so you can take a look at what it involves.

 

Thanks, I'll have to give it a shot when we get a 2nd running vehicle again. It seems like a likely source of the problem since it seems to come from both sides of the engine