Low RPM knocking sound.... diagnosis please!
Jul 9, 2003 | 05:08 AM
#21
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Joined: May 2003
Posts: 38
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From: Georgetown, Texas
YKES!
Originally posted by Jay
By pulling the plug wire for a specific cylinder you have releaved that cylinder of the forces of combustion. Thus eliminating the stress on that cylinder.
That is a common test when diagnosing "lower end" noise. I regretfully inform you that you indeed may have a serious noise. The possibilities are few, a) Excessive connecting rod bearing clearance b) Loose / Worn wrist pin c) Collapsed piston skirts. All of which requires engine removal and usually machine work to correct properly.
By pulling the plug wire for a specific cylinder you have releaved that cylinder of the forces of combustion. Thus eliminating the stress on that cylinder.
That is a common test when diagnosing "lower end" noise. I regretfully inform you that you indeed may have a serious noise. The possibilities are few, a) Excessive connecting rod bearing clearance b) Loose / Worn wrist pin c) Collapsed piston skirts. All of which requires engine removal and usually machine work to correct properly.
Jul 30, 2003 | 11:38 AM
#24
Guest
Posts: n/a
pinpointed but not fixed
OK, here's the diagnosis, but not the fix...
I had some more clues that moved me to look at the transmission.
1. If i revved the engine quickly up through 1000-1500 i can hear the noise. If i SLOWLY rev the engine through those rpms, i hear NOTHING.
2. If i held the gear selector for my auto tranny, i can feel a slight pulse each time i hear the knock.
3. It makes the noise much louder when the truck is in gear and under stress (acceleration).
So, i went to the dealer and had a transmission flush. It was time anyway, so i just had it done. The problem went away almost 100%!!!
So, my diagnosis is that the noise happens when the front side of the Torque Converter is out of sync with the rear side and at low rpms. I say that because slow revving of the engine allows the rear side to stay in sync with the front and not make the noise. If i rev it fast, the rear has to accelerate its spin to catch up and whammo, there's your noise. I don't think it is anything forward of the torque converter since the flush cured the problem for a bit and the noise happens AT engine rpm, so it must be related to the torque converter and not anything further back in the transmission...
I don't know why pulling the plug wire for #1 helped the noise. Maybe when that cylinder doesn't fire it relieves the pressure off the TC just enough that it lessens the noise, but i'm 100% sure it is not engine now.
I'm so confused how this could just start happening. I mean a torque converter is just a damn turbine, it shouldn't wear out or make noise! GAH. Any help, as always, is appreciated.
J.
I had some more clues that moved me to look at the transmission.
1. If i revved the engine quickly up through 1000-1500 i can hear the noise. If i SLOWLY rev the engine through those rpms, i hear NOTHING.
2. If i held the gear selector for my auto tranny, i can feel a slight pulse each time i hear the knock.
3. It makes the noise much louder when the truck is in gear and under stress (acceleration).
So, i went to the dealer and had a transmission flush. It was time anyway, so i just had it done. The problem went away almost 100%!!!
So, my diagnosis is that the noise happens when the front side of the Torque Converter is out of sync with the rear side and at low rpms. I say that because slow revving of the engine allows the rear side to stay in sync with the front and not make the noise. If i rev it fast, the rear has to accelerate its spin to catch up and whammo, there's your noise. I don't think it is anything forward of the torque converter since the flush cured the problem for a bit and the noise happens AT engine rpm, so it must be related to the torque converter and not anything further back in the transmission...
I don't know why pulling the plug wire for #1 helped the noise. Maybe when that cylinder doesn't fire it relieves the pressure off the TC just enough that it lessens the noise, but i'm 100% sure it is not engine now.
I'm so confused how this could just start happening. I mean a torque converter is just a damn turbine, it shouldn't wear out or make noise! GAH. Any help, as always, is appreciated.
J.
Last edited by J; Jul 30, 2003 at 11:42 AM.
Jul 30, 2003 | 06:33 PM
#26
Contributing Member
Joined: Dec 2002
Posts: 2,424
Likes: 0
From: The Lone Star State
Originally posted by J
The problem went away almost 100%!!!
The problem went away almost 100%!!!
That's just my $.02.
Jul 31, 2003 | 05:23 AM
#28
Registered User
Joined: Nov 2002
Posts: 109
Likes: 0
From: Ballston, VA
i really wish i knew more about transmissions and/or how engines work. it'd probably make things a lot easier. my noise just seems to get worse every day. until a few days ago, the engine would have to warm up a bit before the noise came, now, it starts clanking as soon as i fire her up. unfortunately for me, i don't have the money to fix it now, so i'll just have to stay on local roads until i get a job and save up. 
Mar 10, 2022 | 11:00 AM
#29
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Joined: Mar 2022
Posts: 1
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I see that this is a very old post, but I think my Rav 4 is doing this same thing. It’s a 2017, started around 90,000 miles. Currently at 98,000. It’s a low idle knocking, that disappears after maybe 2 or 3 gear. It’s present in park, low idle. One other thing, is that when you rev the engine, and let off the pedal, there is a whirring sound that starts high pitched and then tapers off as it disappears.
I thought it sounded like piston noise, ran a couple injector cleaners through it, bumped up from 87 to 89 octane. Disappeared for a week or so. Came back, tried seafoam in the gas tank, took it right away. Now it seems like every tank that doesn’t have sea foam, the noise is there. Every tank with sea foam, it’s gone. Seafoam would be an expensive way to operate. Also put seafoam in the oil reserve. Oil was just changed, noise is worse. I’m going to put it in the oil again and see how that goes. I read the 10w30 comments and think that sounds like a good way to go. It sounds like something isn’t lubricated well enough. When it first started, I had just had an oil change, and I was worried they maybe just “didn’t put any oil in it” that about gave me a panic attack. But they had, so that really didn’t relieve any worries.
Also it’s of note that it seems to be air temperature related. Seems to be present on colder days, and absent on warm days… seems to be. Idk
I thought it sounded like piston noise, ran a couple injector cleaners through it, bumped up from 87 to 89 octane. Disappeared for a week or so. Came back, tried seafoam in the gas tank, took it right away. Now it seems like every tank that doesn’t have sea foam, the noise is there. Every tank with sea foam, it’s gone. Seafoam would be an expensive way to operate. Also put seafoam in the oil reserve. Oil was just changed, noise is worse. I’m going to put it in the oil again and see how that goes. I read the 10w30 comments and think that sounds like a good way to go. It sounds like something isn’t lubricated well enough. When it first started, I had just had an oil change, and I was worried they maybe just “didn’t put any oil in it” that about gave me a panic attack. But they had, so that really didn’t relieve any worries.
Also it’s of note that it seems to be air temperature related. Seems to be present on colder days, and absent on warm days… seems to be. Idk
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