Now With Video!

The title says it all, but I'll elaborate. 1987 F350 6.9 IP glowplugs and injectors replaced 13k miles ago and the engine has been starting and running great. It leaked oil though, so I parked it in the shop 3 weeks ago & have been working on my front end, & decided to replace valve cover gaskets- they were both leaky. The passenger side was worse than the driver side and I went ahead and replaced both with new Fel-pro rubber gaskets and I applied black RTV sealant to the cover & torqued my bolts all to 6lbs.

I started the truck and there is now a knock that was not there before. The knock increases in speed when I throttle up. It is more noticeable when I am in the cab with the doors closed and windows up than when I am looking at the engine with the hood up. When I place my hand on the valve cover, I'm not 100% sure if I can feel anything knocking on it.

Could I have caused this problem though some careless maneuver in changing the VC gaskets? Other threads relating to knocking noise have directed people to run the motor with the VCs off. If I carefully take my covers off to inspect, do I need new gaskets? Do I have to remove gaskets & sealant and start all over? When I parked the truck it was about 35 degrees and its down to 15 now. How should I move forward on this? Thanks!!

 

thats just a bad coincidence.sticking injector maybe? they sound pretty nasty like a loud rod knock.don't have a bad oil leak do ya? she leaked out and now low on oil in the 3 weeks parked? did ya check oil level? likely you shut it right down and checked asap,but can't hurt to make sure.

 

Thanks for the reply. The oil level is Ok, leak wasn't too severe. Injectors I could look into.

I went over to where she's parked today and took some audio from under the hood and from in the cab. Maybe this sounds familiar to one of you guys?

 

I know that sounds anywhere.....Its a sticking exhaust valve.....

 

OK, now back from my turkey day travels and I need to fix this problem.

I'm trying to understand whats going on here that is creating the problem. I've got my Haynes diesel engine repair manual, but that is not giving me all the answers. Is my piston knocking into the stuck valve and creating the noise?

How should I go about correcting the sticking exhaust valve? I figure I need to determine which side it's on and then once I have the cover off, how do I tell which valve it is? Then once I think I've isolated the problem valve how do I get it unstuck?

Lastly- the lazy guy in me wants to know if this problem might have arisen from the truck sitting in the cold and I want to know if its OK to take a 30-60 minute drive and get everything warmed up again to see if its OK.

Thank you!!!

 

I am not sure it is a sticking valve. But since a diesel relies on compression the sticking valve may prevent pressure build up and just cause a dead cyl. If you have a dead cyl due to a sticking valve you should be able to isolate the cylinder by loosening the injection line to see if the cyl will miss or stumble. If you loosen the line and the engine rpm's does not drop that is the missing cyl.

If it is a sticking valve you can pull the valve covers and bring each cyl's valves to the closed position (TDC or power stroke) and see if you have a loose rocker arm or the heights are not the same. Maybe you have a weak or broken valve spring.

If you do have a sticking valve or a valve that does not seat properly you can bring it to TDC and remove the rocker arm, keepers, spring, and valve seal. Inspect all your parts for wear. Lubricate the valve stem at the valve guide and work the stem up and down as you rotate it. I have used carb cleaner at times to remove gum build up. For valve seats, I have used an air drill clamped to the stem, using gentle upward pressure as it rotates to help clean up the valve seat. Lube valve stem and replace valve seal with new unit. Crank engine over, with injector or glow plug removed to remove any combustible cleaner, if needed.

Good luck, and keep us posted.

 

If I crack all injection lines and there is an RPM drop for every one, does that mean no dead cylinder --> no stuck valves?

 

If all the cyl's drop (one at a time) then every cyl' is firing. You may notice that some cyl's drop more than others and some just barely drop at all, I would be concerned with the weak cyl's.

You may have an intermittent sticking valve or a valve that is not seating properly. Since you should not wet test a diesel engine, I guess the best way to check the valves is with an air test and listen for air in the intake or exhaust system.

A sticking injector sounds very loud and knock-like. IMO, I think your noise is coincidence or maybe it was there before you started the valve cover gasket R&R. I did hear some intermittent valve train noise in your video, but it is more accurate in person. Loosening the injector lines should eliminate a sticking injector the same way you listen for a dead cyl.

 

I loosened the fuel supply line nut over each injector and observed an equal drop in RPMs across all cylinders. Then I drove it for a while, but its still making the knocking noise.

I'll need to familiarize myself with air testing the valves, because I have no idea what I need on hand besides a compressor to do that. Anyone have a link to a howto page on that? I dont know if I need a special fitting or where to blow the air into once my valve covers are off. I get the concept though- you blow air in and if you hear air passing thru the exhaust pipe or the air intake (with the air cleaner removed, right?) then you have a bad seal on that valve.

Also, does anyone have any other opinions on what could be making that dang knock? It doesnt get louder when I accelerate and drive, the engine noise drowns it out. When I give it a little throttle though you can hear the knock-rate increase.

 

I guess the official term would be a cylinder leak down test.

I use a spark plug adapter to test the valves and a compression tester to test the rings, you will need a injector or glow pug adapter that will fit an air compressor.

Did the knock noise go away when you happened to loosen the fuel line? If so, that is MOST LIKELY the cylinder, AND may actually be a bad injector and nothing more.

 

This problem turned out to be related to an injector. 2 years ago I replaced all injectors and the shop where I got them returned my old ones- 3 were still good.

I needed a buddy for this because the knocking noise could only be heard from inside the cab. So when I cracked the return line over the bad injector and the noise went away, I simply put one of my old ones back in.

I'm still wondering why one of my new ones would fail so soon.

Anyway, I just wanted to follow up on this thread that I started. Thanks for your help guys!