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Trying to diagnose a new knock

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Old 08-08-2018, 12:03 PM
grizzlyjosh
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Trying to diagnose a new knock

Hey folks, my '93 has recently developed a loud and scary knock. I have been scouring this and other forums to try to figure out if I'm dealing with a head gasket problem, an injector issue, an oil cooler issue, cavitation or something else I don't even know about but nothing seems to sound exactly what I've got going on. The knock is seemly random at idle but more frequent and louder at higher rpms/under load (I attached a video). I can't really tell if it seems top end or bottom end (maybe louder from the bottom?). Other symptoms were low coolant, though I just topped it up (maybe a gallon) and after driving around for 10 miles no noticable change. It is possible that the cooling system has a small leak that I haven't noticed and is low for that reason. No bubbling or other signs of pressure into radiator when run with the cap off. Heat still works. There is a fairly strong steam out of the oil filler when running, but its been like that since I got it 50k miles ago. It is smoking (greyish) even once warmed up, not much at idle but stronger at higher rpm. The smoke doesn't smell like antifreeze. The oil level has been constant and doesn't look grey on the dipstick but I haven't drained it to see (I'm being cheap, I JUST changed it). As far as driving goes, no noticable loss of power and it starts right up.
I just did an injector test by turning off the key while driving downhill at ~1600 rpm and the knocking persisted with the key off.
I think the next thing I'll do is pull valve covers and see if anything looks wrong under there.
What else can I do? Any thoughts on a possible diagnosis or what to try next?
Well, can't seem to upload the video...
 
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Old 08-08-2018, 01:20 PM
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Have you tried to isolate the sound with a mechanic's stethescope? You might be able to rent one from the auto parts store if you don't have one. You can always use a long screwdriver as a stethescope by placing the screwdriver on the engine and putting the screwdriver handle to your ear.

https://www.amazon.com/Lisle-52750-Stethoscope-Kit/dp/B0015DLMOO/ref=sr_1_1?ie=UTF8&qid=1533752304&sr=8-1&keywords=mechanics+stethescope&dpID=41%252BoshO-N3L&preST=_SY300_QL70_&dpSrc=srch https://www.amazon.com/Lisle-52750-Stethoscope-Kit/dp/B0015DLMOO/ref=sr_1_1?ie=UTF8&qid=1533752304&sr=8-1&keywords=mechanics+stethescope&dpID=41%252BoshO-N3L&preST=_SY300_QL70_&dpSrc=srch
 
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Old 08-08-2018, 02:02 PM
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These engines have a lot of blowby by design so what's coming out of your oil fill is more than likely no concern.
You can try cracking you injectors one at time while the engine's running to check the injectors.
If you can't upload the video here put it up at youtube and post the link here.
 
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Old 08-08-2018, 06:55 PM
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I would pull the glow plugs and look for signs of water or rust. Mine definitely had a gentle knock at idle and got louder when under load, but it was also pushing coolant out the radiator, never got hot though and still ran fine other than that
 
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Old 08-08-2018, 09:06 PM
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Ok, I got the video on youtube. Here it is:
. And here is another one of the tailpipe and how it seems to puff smoke almost immediately following a knock: https://www.youtube.com/watch?v=7LTu...ature=youtu.be.
 
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Old 08-08-2018, 10:00 PM
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Yikes. That's not good. I don't think that's a bad injector.
 
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Old 08-09-2018, 05:54 AM
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Originally Posted by grizzlyjosh View Post
Ok, I got the video on youtube. Here it is: https://youtu.be/lXzU3ToIS10. And here is another one of the tailpipe and how it seems to puff smoke almost immediately following a knock: https://www.youtube.com/watch?v=7LTu...ature=youtu.be.
That sound like a rod knock. It may be time for new bearings. Either way check the oil pressure with a mech gauge.
I had 7.3 that starting knocking like that and it actually had a rod cap nut back off. Either way I think you are going to be opening up the bottom end.

 
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Old 08-09-2018, 06:38 AM
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Sounds like valvetrain noise to me. Maybe a push rod/rocker arm/stud/valve stem connection.
Screwdrivers can work, but are so 60's. Stethoscopes are now very inexpensive, and work so much better than a screwdriver.
 
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Old 08-09-2018, 07:29 AM
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Originally Posted by Dieselamour View Post
Sounds like valvetrain noise to me.
x2

It doesn't sound regular or deep enough to be bottm end noise IMHO. Definitely check your oil pressure and let us know the results.

 
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Old 08-09-2018, 09:40 AM
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Ok, I'm not sure how to check the oil pressure. Where do I hook up a gauge? Can I put a tee onto the nipple on top of the Sidewinder and read it there? And I have a pressure gauge that I've used for the fuel system, will that work or do I need a different gauge?
I pulled off the valve covers and things look pretty normal. I can't see any bent push rods, the rockers rock when turned over by hand, there is oil on everything. Is there something else to look at? The only weird thing was condensation/grey sludge on the inside of the valve cover, though the oil pooled up on the rocker arms was normal and black.
 
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Old 08-09-2018, 09:42 AM
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Originally Posted by Dieselamour View Post
Sounds like valvetrain noise to me. Maybe a push rod/rocker arm/stud/valve stem connection.
Screwdrivers can work, but are so 60's. Stethoscopes are now very inexpensive, and work so much better than a screwdriver.
Valve train noise would be consistent and in these IDI's it is very tough to pick out over the normal diesel knock short of being out phase with it. This is more than likely rod bearings as when they start to go they knock consistently under load and intermittently with no load. Regardless an oil pressure test will reveal all
 
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Old 08-09-2018, 11:45 AM
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The way it was intermittent made me think it could have been an accessory bracket that was loose, and it was banging on something as the engine vibrated. But the more I listen to the audio, it makes me wonder if it's on the bottom. I'd expect it to be more consistent if it was a bearing, but maybe it's just starting to fail. Either way, oil pressure will tell.
 
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Old 08-09-2018, 11:47 AM
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If your oil pressure is normal, try pulling the belts one by one, and see if the sound continues.
 
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Old 08-09-2018, 05:15 PM
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I just hooked up an oil pressure gauge. Warmed up and at idle, it was at about 25 psi, if I revved it (don't know the rpms, I was doing it by hand because I just have the gauge under the hood) it would go to about 40. What is it supposed to be? And what does the oil pressure tell me? I noticed that the knock doesn't show up until the engine is warmed up. Also, I could feel the knock when I had my hand on the black bladder-looking thing that says 'Sidewinder' on it. It was also loudest listening with the stethoscope there. Could it be something with the turbo? I don't have a boost gauge but I have been noticing that the EGT's have been a little higher (going up the same hill on the way home) then they used to be. The injectors all sounded about the same. And I'm not sure where else to listen to with the stethoscope.
I also ran it this last time with the valve covers off so I could watch them and didn't see anything out of the ordinary. Is condensation on the underside of the valve cover something to be worried about?
 
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Old 08-09-2018, 05:28 PM
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If you have good oil pressure (25-40psi is great for an IDI), then that eliminates the collective worry that you have a bearing failure. If you had a bearing go out, you'd have a knock like you have, but no oil pressure cuz the bearing won't have the proper spec tolerance to restrict the pressure.

So that's good news. Also, if you are hearing it from the turbo area, that could be a good thing. At least, good thing relative to what I was worried about.
 
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