As many of you probably already know I have an 84 F250 4x4 with the 6.9 IDI diesel C6. For the past few month's my truck has had a bit of a knock/rattle/clattery sound to it. What is weird about it is it comes and goes when you get on and off the throttle, but not consistantly. I thought it sounded like it was coming from the bellhousing area. Last night I popped off the inspection cover and checked all the torque converter nuts, all were tight. Then I got up in there with a prybar to see if the flexplate had any movement, none of course that I could see. It didn't seem to have excessive end play in the crankshaft. I couldn't see any shiny spots where anything was hitting or rubbing. I suspect maybe a cracked flexplate? I don't think it's the injection pump as it was rebuilt last summer, all eight injectors were replaced 3 years ago. Could it be something is out of adjustment, timing etc? The engine runs really smooth has decent power, get's good oil pressure... 40 psi going down the road, and that's from a mechanical guage. I guess I'm a little stumped here, does anyone have any suggestions? Thanks in advance!
John

 

wonder if you might have an injector plugged or failing.sounds kinda similar to what mine did when i had a bad one.let it run or drive it for 5 or 10 minutes shut it off and feel the hard fuel lines and see if one is hotter than the others.do this when it seems to act up more.or just give it a treatment of ATF or diesel kleen. that will atleast help the fuels system and wont hurt nothing.that would be where i would start first its cheap and easy.there are a few things it could be though

 

Have you checked the 4x4 driveline...... you did say TRUCK not engine specifically??

 

Does it do it at all speeds? Mine was doing something like that when I was going kinda slow, turned out to be worn break caliper pins...

 

is it rhythmic? does the noise seem to match the wheel or drive shaft speed? does it sound like its comming from the rear end? if so check your rear end. my truck was doing this and turned out to be a broken pinion screw. which allowed the pinion shaft to hit the pinion gear on the revolutions which explains the rhythmic noise. noise would come in and out periodically and sometimes when driving it wouldn't even do it all. so now i am still in the hunt for a replacement rear end. so hopefully better luck to you.

 

Thanks for the replies everyone. I am pretty sure I have it narrowed down to the engine and transmission area. It seems to match with engine speed, I really notice it at lower rpms taking off from a stop or when the transmission shifts into the next higher gear. I can't believe it would be a connecting rod or wrist pin, it has been doing this for a while... it doesn't seem to getting any worse. What's most confusing about it is, it doesn't rattle like this all the time; it comes and goes. I have been kind of thinking it may be an injector acting up or the injection pump. One thing I just thought of might be to watch the engine temp guage (mechanical) when it makes this noise and when it doesn't. Maybe the engine temp would make a difference, I know these engines really clatter when they're first started in cold weather. I do run Diesel Kleen pretty regularly, I have never tried running ATF... I've heard it works well. The only driveline component I haven't been into is the transfer case. It has a fresh C6, all new u-joints, and both front and rear axles have be completely rebuilt. When I did the Dana 60 SAS I installed new calipers with new pins, rebuilt the king pins, new axle joints, new spindle bearings and wheel bearings. The drivetrain in this truck is fresh and super tight, I can't imagine it's anything too serious it just bothers me when I hear it. I am doing a Banks turbo install this spring, I want everything to be in perfect working order before doing so. Thanks again, any and all suggestions are appreciated.
John

 

I would vote fuel system. With my failing IP and off pressure system, i am positive it is the IP and possibly injectors. I replaced the injectors not that long ago but you never know. When i replace the IP everything goes. IP Injectors and steel lines. The intank pumps will be disconnected too and a Mr Gasket 12D will be installed so the IP can be properly timed. From there i can decide what is the best setting and get it reset. So yeah, extra clacking or rattling is definitely the fuel system if you can rule out everything else. Especially how you say it comes and goes. I notice when i get any fuel but the shell station it is louder. That Vpower diesel makes it run a lot quieter. That and when i use 2cycle oil it is even quieter. So best luck, but i bet fuel.