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#44513 - 02/12/06 04:24 PM Knocking noise at idle and low revs
Anonymous
Unregistered


I've searched exhaustively for this but so far can't seem to find anyone who has the same symptoms under the same conditions. This sounds like a much heavier rattle than lifters or a heat shield, noises I'm somewhat familiar with from owning a Miata...

At idle, I can hear a slight knocking noise. I crawled under the truck to listen while it was idleing in neutral and it seems like it may be coming from the bellhousing area, but it's hard to tell. If I rev the engine with the clutch in, such as taking off away from a stop, the noise is much louder and almost sounds to me like an engine that is low on oil (checked that, it wasn't). It makes the sound between 500 - 2000 RPM in idle, first, and second gears, but I don't hear it in the higher gears. I thought that it might be a low oil pressure issue, but then I think it wouldn't matter what gear it was in?

Somewhat worried that my new-to-me truck might be ready to throw a rod, I asked a local Nissan dealer and was told that it didn't sound like an internal engine problem, but maybe a loose flexplate. :rolleyes: Maybe he meant flywheel...

I tried unplugging the EVAP solonoid as per the TSB that I found on here, but the noise is still present and doesn't seem to be coming from that area of the truck at all.

Anyone have any new ideas?

Thanks in advance.

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#44514 - 02/12/06 05:58 PM Re: Knocking noise at idle and low revs
Anonymous
Unregistered


i had a knocking in my old dodge truck. it was because of no tune up at the 50 or 100 thousand mile markers. basically i fixed it by putting premium gas in it. have you done the 90k tune up? its just replacing the spark plugs i think but that might help you out.

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#44515 - 02/12/06 06:16 PM Re: Knocking noise at idle and low revs
Anonymous
Unregistered


Getting ready to do the tune-up soon. I forgot to mention, the truck just turned over 59k miles. Getting ready for the 60k service. Thanks for the suggestion.

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#44516 - 03/12/06 04:32 PM Re: Knocking noise at idle and low revs
Anonymous
Unregistered


I changed the oil and went out and bought a "mechanics stethescope". I can't really hear much through it, however, if I put it against the clutch fork, I can feel it vibrating along with the noise. Has anyone ever heard of a clutch or throwout bearing making this kind of noise? confused

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#44517 - 03/12/06 05:57 PM Re: Knocking noise at idle and low revs
Anonymous
Unregistered


what is the 60k service? i got mine with 72k so i didnt know if it need anything..nissan told me that the 90k was basically just replacing the plugs..but i dont know.. its probably something minor as it is and can be fixed quickly.

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#44518 - 07/12/06 04:51 PM Re: Knocking noise at idle and low revs
Anonymous
Unregistered


I think the 60k service is just changing the oil/filter, inspecting some things, and lubing the hubs and propshaft.

I took the truck in to Carmax today as it's still under the 30-day warranty. The tech that rode with me said that he thinks it's the pressure plate, so it looks like I'm going to have that replaced. Hopefully that's really what the noise is.

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#44519 - 22/12/06 06:21 AM Re: Knocking noise at idle and low revs
Anonymous
Unregistered


Got the truck back with the new clutch assembly. I still hear the noise, however, it MIGHT not be as loud as it was before. I'm planning on having an oil analysis done just to try to be a little more sure it's not something banging around inside the engine.

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#44520 - 22/12/06 10:19 AM Re: Knocking noise at idle and low revs
hansojc Offline
Member

Registered: 15/10/02
Posts: 69
Loc: Columbia, S.C.
I've got a knocking noise in the "bottom end" of the motor somewhere. My mechanic couldn't zero in on it without pulling the engine apart. Mine is really loud @ 1500 - 2000 rpm's.....then un-noticeable @ higher gears and speeds. Mine's a 2000 with 140k miles on it. According to the mechanic, I have a lot of sludge build-up in the motor. I'm just living with it until it eats itself or I can afford to trade it in, as it is not worth having an engine re-build or swapping motors. The truck's only worth about 3 grand......no telling what a re-build or motor swap would cost.

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#44521 - 22/12/06 12:44 PM Re: Knocking noise at idle and low revs
Anonymous
Unregistered


Hmm, that sounds similar to mine, but I don't know how to tell if it's coming from the bottom of the motor or what. It does sound loudest right around 1000 - 2000 RPM though. Any idea how he could check for sludge w/o pulling the oil pan?

I've found pulled X motors on ebay in the $1,200 - $1,500 range, so I figure I'll go with that if worse comes to worse and warranty doesn't cover it...

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#44522 - 22/12/06 07:46 PM Re: Knocking noise at idle and low revs
Anonymous
Unregistered


For sludge build up try using Seafoam in the crankcase, But remember to change the oil after a few hundred miles. You might also have to do an upper engine cleaning with Seafoam.

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#44523 - 27/12/06 07:53 AM Re: Knocking noise at idle and low revs
hansojc Offline
Member

Registered: 15/10/02
Posts: 69
Loc: Columbia, S.C.
He did pull my oil pan when he found the sludge, I don't know how you would do it otherwise.....unless you can pull off the valve cover an tell.

My Seafoam experience exposed a lot of issues with my truck, so be careful. Apparently all my seals were sealed and working because of the build-up on them. The seafoam treatment cleaned all this out and all my seals began leaking......but I guess this was a blessing because I had no idea about the condition of the internals of the motor. I actually found an honest mechanic that knows his stuff about foreign motors.

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#44524 - 17/02/07 10:42 PM Re: Knocking noise at idle and low revs
Anonymous
Unregistered


I think I have clutch problems.

As an update to this, Carmax replaced the clutch under waranty and send the flywheel out to be resurfaced at a 3rd-party machine shop. I think the noise is still there, but it seems to be a lot quiter. People that ride with me say that it is not nearly as loud.

HOWEVER, now I noticed that if I try to disengage the clutch above 4,000 RPM, it won't disengage. Keep in mind, I don't have a habit of going this, but I have noticed it on one or two occasions. I've noticed that even if I rev the engine with the trans in neutral and the clutch pushed in, I can feel a decrease in pressure from the clutch pedal once the engine passes 4k. If I try shifting at the redline from 1st to second gear, the clutch pedal stays on the floor until the engine's revs drop.

I've tried the test to see if my clutch is slipping and it doesn't seem to be. The truck easily can squeal the tires in first gear, and if I put it in second at low speeds and rev the engine and let the clutch out I get a chirp from the tires, so it doesn't appear to be slipping at all.

Anyone have any idea what would cause this? Could this happen if the machine shop didn't step-cut the flywheel properly when they resurfaced it?

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#44525 - 19/02/07 04:48 PM Re: Knocking noise at idle and low revs
Anonymous
Unregistered


Sounds like you may have a loose or not properly installed flywheel, I heard the same noise on many 1983 - 1987 Chevy 3.8 V-6 (automatic) fleet vehicles. All that was needed was to remove each bolt and add lock-tight. We could get to them through the inspection cover.

Sorry I did not see your post earlier, Fab.

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#44526 - 20/02/07 12:58 PM Re: Knocking noise at idle and low revs
Anonymous
Unregistered


I used to have a 90 jeep Cherokee that had a similair noise issue. for me it turned out to be an exhaust leak by the engine that I could hear under it at idle. Plus a loose/warn out U Joint at the rear axle (it would rattle at acceleration and vibrate as well, but at higher speeds/rpms nothing. The u joint finally snapped a bolt on day, so after replacing it the loud rattle at acceleration that sounded like it was in my transmission was gone. It sounds like you might be tracking it down to your clutch, but it might be something to check out just to make sure all those bolts on the joint at tight.

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