Engine knock, only when warm and at idle?

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So I'm wondering what you guys think of my issue. I have a 92 Supra that's making an odd knocking noise from the engine and I can't figure out what it is.

There's a few interesting things about the knock:

1) It only makes the noise at idle.
2) It only makes the noise when the engine is warm.
3) It's an intermittent noise that comes and goes.

I took a video of the engine running and for the first 30 seconds or so of the video, the noise is constant and then after that it becomes intermittent. The noise can be heard from 0:05-0:30 and 3:35-3:45. Any ideas?

https://www.youtube.com/watch?v=fGUY_Cw4MTY
 
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Is the belt tensioner good? I'd check exhaust manifolds and accessory brackets. Hopefully its not rod knock , but thats hard to tell from video sound.
 
Originally Posted By: spasm3
Is the belt tensioner good? I'd check exhaust manifolds and accessory brackets. Hopefully its not rod knock , but thats hard to tell from video sound.


I don't think it's my tensioner considering it only makes the noise once the engine is warm.

It could be rod knock but from what I know, it should be audible at any temperature and rpm but I do hear a bit of rattling from the motor on a cold start that goes away within a few seconds.
 
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Sounds like a rod knock. Disable one cylinder at a time by disconnecting a plug wire or fuel injector to isolate which cylinder it is.
 
Originally Posted By: mehullica
Sounds like a rod knock. Disable one cylinder at a time by disconnecting a plug wire or fuel injector to isolate which cylinder it is.


Huh?? I don't understand this diagnostic procedure.
 
Originally Posted By: dishdude
Originally Posted By: mehullica
Sounds like a rod knock. Disable one cylinder at a time by disconnecting a plug wire or fuel injector to isolate which cylinder it is.


Huh?? I don't understand this diagnostic procedure.


When you remove the ability for that cylinder to contribute to the power the engine makes it will stop loading the rod bearing and subsequently not knock. It is an easy way to isolate which cylinder is making the noise.
 
Thank you for the explanation. I figured the crankshaft was still turning so it would still make noise. Although I'd think with the engine missing it would really make noise no matter which cylinder you have disabled.
 
Originally Posted By: dishdude
Thank you for the explanation. I figured the crankshaft was still turning so it would still make noise.


Nope, when you don't have the power stroke acting upon the rod bearing it stops making noise. We used this method on my buddy's 4.6L in his Mustang (pulled the injector plug) to isolate that he had spun #7.
 
Good stuff guys, I'll pull the injector connectors one by one and let you know what I find.
 
Sounds like either rod knock or low oil pressure on one or all of the rod bearings.
What oil is it? Try a 40 or 50 weight but even if that quietens it down it's only gonna band aid what sounds like a bigger problem
 
Originally Posted By: 19jacobob93
Sounds like either rod knock or low oil pressure on one or all of the rod bearings.
What oil is it? Try a 40 or 50 weight but even if that quietens it down it's only gonna band aid what sounds like a bigger problem


I'm thinking it's low oil pressure too but I don't have a gauge. I'm using M1 10-30. At some points, it sounds like a knock and multiple rattles at once. It just doesn't sound like text book rod knock to me, especially considering the noise is goes away when the idle goes up, even just by a few hundred rpm.
 
Originally Posted By: 19jacobob93
Try a 40 or 50 weight


That's what I'd do,and make sure it's a conventional oil (try pyb 10W40). Imo it doesn't sound like an engine knock because it's too sporadic. Wouldn't an engine knock be present perpetually and match rpm speed?
 
Originally Posted By: aquariuscsm
Imo it doesn't sound like an engine knock because it's too sporadic. Wouldn't an engine knock be present perpetually and match rpm speed?


That's what I'm thinking too. Something is loose but I just don't know what it is. Almost sounds like it's coming from the head. I'm going to unplug each cylinder and see what happens, if it doesn't narrow it down then I guess that's somewhat good news but then it's back to the drawing board.
 
Its summer I'd try a quick change with a cheap 15w40 oil and see if you still get that noise.


Warm low idle is where you would have lowest oil pressure/flow.
 
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Yes, and if you watch the first video I added, you can see that the noise disappears right away when I rev it a bit. I'm honestly leaning towards a lifter issue as this motor uses hydraulic lifters and because the knock noise is very intermittent. I don't know though. What do you guys think about a little bit of oil stabilizer like Lucas and see what happens?
 
Originally Posted By: JZA70
Yes, and if you watch the first video I added, you can see that the noise disappears right away when I rev it a bit. I'm honestly leaning towards a lifter issue as this motor uses hydraulic lifters and because the knock noise is very intermittent. I don't know though. What do you guys think about a little bit of oil stabilizer like Lucas and see what happens?


You'd be better served with a quart of 20w-50, at least it has AW additives in it.
 
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