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Knock at low rpm under load?


Strato_54
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Probably a stupid question but I’m at my shop and was giving the transfer case a work out in the snow but I let it dip to low RPM in 4H and letting out the clutch and right before I stalled it there was a knocking and once it started again it sounded fine. Is this just because of low rpm and under lots of load or something else? I did it twice and each time after it sounds fine. I also have a bad knock sensor bank one so that could also be it

Edited by Strato_54
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If you have a bad knock sensor then I've been told that the ignition is then retarded due to faulty sensor, if true then it should not be the sensor.

Edited by CALPATHY
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5 minutes ago, CALPATHY said:

If you have a bad knock sensor then I've been told that the ignition is then retarded due to faulty sensor, if true then it should not the sensor.

alright makes me feel a little better about not having something more catastrophic. the thing still runs great and drives great so i guess it was just one of those small things

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When the engine is under high load and very low RPM, knocking is normal. It isn't good for the engine since it is metal on metal contact but a few times generally won't be a problem. At the low rpms, there is low oil pressure and flow. The oil flowing at operating pressure normally keeps all the moving parts floating so they don't make actual contact. When the pressure drops low enough, the moving parts like the crank, rods, pistons, and cams come into contact and it is violent and unhealthy. That is why most engine wear happens on cold starts. 

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29 minutes ago, Mr_Reverse said:

When the engine is under high load and very low RPM, knocking is normal. It isn't good for the engine since it is metal on metal contact but a few times generally won't be a problem. At the low rpms, there is low oil pressure and flow. The oil flowing at operating pressure normally keeps all the moving parts floating so they don't make actual contact. When the pressure drops low enough, the moving parts like the crank, rods, pistons, and cams come into contact and it is violent and unhealthy. That is why most engine wear happens on cold starts. 

ok so then user error got it. didnt sound very nice but it still runs fine. had a feeling that was what it was but wasnt sure what i was hearing for those few seconds. it wouldnt have done much hurt as it knocked 2 times stalled and i did it again same thing 2 knock then stall. not under intense load but had enough. should be fine then thanks for clearing my nerves 

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Yep, will be fine. A very familiar sound to people who teach others how to drive a manual transmission. I had an easy one when teaching my nieces, my 85 300zx, but still had the familiar clatter and stall. It gets more interesting when it happens in the middle of a left turn and the niece is panicking while watching the lifted F350 aimed at you at 50 mph. Keeping calm helps a LOT to get the excitable girl to restart and get the car out of the way. I had the job of teaching mine and my sister's kids how to drive because it takes a lot to get me excited. Out of them all, only my daughter appreciates low range and is enthusiastic about using it. 

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2 hours ago, Mr_Reverse said:

Yep, will be fine. A very familiar sound to people who teach others how to drive a manual transmission. I had an easy one when teaching my nieces, my 85 300zx, but still had the familiar clatter and stall. It gets more interesting when it happens in the middle of a left turn and the niece is panicking while watching the lifted F350 aimed at you at 50 mph. Keeping calm helps a LOT to get the excitable girl to restart and get the car out of the way. I had the job of teaching mine and my sister's kids how to drive because it takes a lot to get me excited. Out of them all, only my daughter appreciates low range and is enthusiastic about using it. 

when i was learning stick in this car actually i never got the knock it was either stall or jump. this is the first time ive gotten the knock which was actually learning hwo to slip the clutch up hill. ive always liked the 300zx and even the 240 they seem like theyre kinda fun to play with

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Yep, drove a 280zx 2+2 for a few years before I got the Pathfinder. Had a 75 280z and the 85 300zx. Definitely had fun times with those cars, but was also a bit frustrating at times. The 280s had inline 6 engines that were torque monsters. The 300 had a VG30E, that is why I originally got it, I figured $300 for a good spare engine for my Pathfinder, then I got foolish and decided to fix the car. All my Z cars were manual transmission but by the time I got my Pathfinder in 99, I was done with manuals and didn't find them good to live with. Half hour of city driving and my left knee would start grinding and put me in great pain. I am old, so most of my cars were ancient by today's standards and finding parts got too hard. 

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