Talk me down off the edge, I think the engine is toast

Shadetreemechanic

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I need help diagnosing a knock. I bought a 89 superduty with a rebuilt 7.3. It was not running. Supposedly it quit going down the interstate and never started again. I got it started easily but it knocks loud out of the intake. The PO had been running WVO in it straight, so suspecting bad injectors i changed them with new Uhaul ones I had laying around.
Still knocks.
Compression check showed 450+ on 7 of the 8 cylinders. # 8 would only go to 320.
I pulled the valve covers and ran it that way and the valves seem to be doing what they are supposed to, nothing loose that I could see.
The knock is loud with the breather open, when I put my hand over the intake it seems quieter, though it is still pronounced. Their are no obvious weak cylinders when I loosen injector lines with it running. It does seem way out of balance when I rev it up, like a weak cylinder.
I am just about convinced something is loose in the bottom end. The only other thing I can think of is the DMF which does seem to have about 3/4 inches of play in it.
The truck knocks constantly throughout the RPM range and nothing changes when i push in the clutch.
So, Is there some way to isolate a knock to either the DMF or the bottom end? Would a bad DMF cause the whole truck to shake at idle?
Thanks for any help.
 

eatont9999

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You sir have a bad injector or two. I went through similar symptoms when I replaced my IP and all 8 injectors with matched Delphis. One was bad and it caused the truck to shake at idle and the sound from the intake was as you described.

To save yourself testing fees, make sure your GPs are in good or new condition. You can test the millivolt reading from each after the engine is up to temp. Any cylinders with a reading out of 10 or so percent of the rest should be investigated. Swap a GP with a normal cylinder before removing the injector to verify it is not a bad GP.

This method worked for me and I replaced my defective injector and haven't looked back since.

Another test to do is put the truck in reverse and if it shakes more as it moves, that is a sure sign of an uneven power stroke. I have an E4OD so I am not sure if that will work with the ZF5 but I see no reason why not.
 

Shadetreemechanic

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I have replaced all 8 injectors with new rebuids and no change. The glow plug circuit is dead and I haven't tried to diagnose it yet. Most cylinders are approaching 500 PSi of compression, so once I got it started this morning with a shot of ether it has started quickly with just latent engine heat.
 

RLDSL

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Or rather a combination of things. bad injectors coupled with a DMF that is toast makes for a real noisy combination. One or more firing unevenly combined with that much play in the flywheel would lead to a heck of a racket.
Wouldn't hurt to check your valve springs just to make sure you dont have any broken ones amd do a cylinder leakdown test to see where that extra comoression is going on number8. If its slipping past a valve you may have a problem, but if it's just going past the rings , I wouldn't worry about it. chances are it just needs a good cleaning with Auto Rx
 

eatont9999

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I second what RLDSL said. The GP test doesn't need the glow plug controller to be working. You just need good glow plugs. You take the connector off all of them and test each one individually for millivolts. I Bought new Delphi injectors and I chased my tail for months because I couldn't believe new injectors could be bad. The injectors I bought were even pop tested and matched. Sometimes machining debris stays in the injectors and causes problems once installed and run.
 

Shadetreemechanic

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does the valve action and spring pressures check out on #8?

I pulled the valve covers and the pushrods and rockers seemed tight. It seemed to have full action on all rockers when I ran it without the covers. Is there some way to do a better test on the valvesprings?
I have been thinking in the night about jamming some shims between the two plates of the DMF to see if I can quiet it down for a minute or two.
Is that insane?
 

rhkcommander

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wvo can thicken quite a bit especially in winter, get it nice n warm and see if that breaks it down. IP and injectors might just be wore out. running wvo is different than wmo in that you want the wvo hot from holding to delivery and before shutoff time flush it out with the other tank being straight diesel or w/e non wvo concoction. Now thats not a must, but that would be the ideal system...

good luck :angel:
 

Shadetreemechanic

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I made a video of the truck running.
http://s1180.photobucket.com/albums/x411/wnw1/?action=view&current=DSCN5849.mp4

I loosened all hard lines individually again while it was running. All 8 cylinders are working and the knock doesn't go away with any cylinder loose.
With the garbage this thing had in it for fuel is amazing it runs at all. I am going to change the fuel filter, though I can't imagine that will help the knock issue.
 

FordCoalRoller

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I will tell you what it sounds like to me and I will tell you this is from experience with a totally different engine but sounds are quite similar. Thankfull being in the military as a diesel mech i get to work on a lot of different stuff. I had just replaced the head gaskets on a 903 cummins. That is a n/a v8. Being that it was an industrial type engine the valved all required adjustment(not like our engines). While adjusting them the rockers on one cylinder of the intake valves became unadjusted to its proper specs(probably bumped it orgot in a hurry). Anyway when we fired it up that sound your is making is alot like the sound that 903 was making. This was due to the intake valve being out of adjustment and releasing compression that had been built up. So with that long winded speak being said I would start checking your valvetrain a little more closely. I have my truck and a buddies both with bad dmf and neither sound like that. I definitely think something is not right in yourtop end. Also could explain the low compression with cylinder 8.
 

trapper

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i had that sound out of the intake b4 and it was a dead lifter and it was chugging air due to it not opening the valve all the way , but after a while it would build up pressure in the lifter and stop the noise
 

86ford69jw

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It sounds just like my old 86 6.9 only louder. I belive it is a bad rocker or vavle. might have to remove to the head and check out the valves. its pretty clanky. mine was more of a thud. good luck man.
 

Shadetreemechanic

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Drove it around the block. It almost went away once when I neared 3k RPMs.
It is blowing alot of white/blue smoke too.
I guess I will pull the valve covers again and take a closer look.
What should I be looking for?
 

FordCoalRoller

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The problem might not be visible from the top side of the head unfortunately. Obviously blue/white smoke indicated oil burnin or runnin lean condition. There is a way to remove valve springs without removing the head. you could remove those and get them checked if you dont have the tool to check the tension.
 
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