It's time to play NAME THAT VQ35 sound!!!
 

Ok, this is the car i've been working on, and it runs fine, starts up fine, and idles fine. But every 20 seconds or so the idle drops, and it makes this HORRIBLE clunking sound.

Here's some possible solutions:

I'm leaning towards this: LEAN CONDITION - the fuel isnt getting to the engine, as the psi is a bit low (but i could have a faulty fpr gauge)

Not enough tranny fluid - this was actualy a bit low, it could use 2 more quarts IMO.

Not enough oil - The dipstick reads "high" when car's warmed up, but maybe there still isnt enough oil.

Other than that, I dont know what it could be.

If it was valves, the car would have this sound constantly. The car revvs great, and above 1000 rpms the sound is gone. It's just when it drops, it starts clunking.

Here are the vids:

http://www.youtube.com/watch?v=pWnzeSby8gg

Inside the car:

http://www.youtube.com/watch?v=HR6R112gfrU

Any help would be appreciated.

Thanks,
-Freddy

:scratch:

Dude, that noise sounds a hell of a lot like a rod knocking to me.

Have you tried putting in a heavy oil? That sounds bad and can definetely be something broken or on the verge of breaking. I would suggest either taking it apart to look for damage or just look into a new engine. It just doesn't sound normal even if the fuel pressure was low.

hmmm ... why does it sound normal when its reved up though??

sounds more like a rattle...something caught in your IM? That's freaking scary sounding....

:noes: :noes: ....:( .. no theres nothing caught in the IM ... ive listened to this car in person, up very close to the motor .... something is wrong ... God I hope its nothing serious ..... if someone can suggest the problem and Freddy and I can fix it properly, you will receive $100 in your paypal account, you will have to pm me

i think it might be the auto flexplate/TC. I'll give you an update tomorrow.

Either way the motor is going to have to be torn down at least partially to discover what's causing the noise so you might as well do it now.

I don't think the motor would run if that flexplate was that much out of alignment.

I'll check the TC bolts tomorrow. I strongly doubt something is wrong with the engine itself. It revs fine, and exhibits no knocking at rpms higher than 1000. Even most times below 1000 it's fine. I know it knocks ALOT less when it's hot, leading me to believe it's a lubrication problem.

10frijoles

i'll try to avoid that, but if it comes down to that, I can do it on the weekend.

It can be several things 1 would be a spun bearing. You should stop the car immediately once you hear any knocking, otherwise you are eating the crankshaft journals beyond repair. You're also contaminating all the oil passages and crevices in the block. Not good. You might end up replacing everything from shortblock, crankshaft and even oil pump. If you hear this stop the engine immediately! Don't try to convince yourself its something easy to fix and not knocking....

If you change the filter & oil, take a pic at the metal shavings and post it. Different kind of metals are used in manufacturing so most probably we can tell whats affected. Its a long shot but it will give you an idea.

or as quoted from a friend himself
"My brother in law (who races pro comp eliminator NHRA) told me the easiest way to tell if it is a rod bearing is to put in some super thick oil, like deisel oil 15 W40.. if the knocking seems to go away or lessen its because the oil pressure builds up.. this could be why when you and I both rev the motor the knock goes away.. so if it goes away or lessens with the thick goo it is most likely a rod bearing.. I know this is a crude test, but I just did it and sure as F$%& it almost completely went away... lame"

or you can unplug each ignition coil one at a time until the knock disappears so you can narrow down the knock to a specific cylinder.

If you have such knocking at a cold engine it is most likely piston slap. When it´s going away after heating up the engine it´s because the pistons are expanding.
If the knocking appears when the engine is getting warm it´s because the oil is getting thinner when hot and can´t dampens/egalize the loose in the rod bearings anymore.

But for me it sounds (at least in the clip) also like a bad rod bearing. Discharge the oil of the oil filter in a white plastic plate or so and check in the sunlight. If metallic fragments are in there a bearing is gone.

or it can be a drive belt tensioner... check the flex plate as well

honestly there is no definite answer, but you have nothing to lose by checkn all of these

im no expert in maximas, but i do have a decent amount of knowledge in building Supras(mk4s)

good look and please tell us when you do find out, its hard to diagnose anything from online

ps- I would also try pulling the valve covers off and running the engine, it could probably be coming from one of the camshafts.. hardest part is, is that the problem can either lie in the shortblock or head but like i said, try everything

is a failed rod bearing intermittent like that? It runs fine for awhile, i'm trying to rule out any engine internals, but im gonna change the oil, and see if that does anything, and i'll also check for metal shavings. If need be, i'll pull the timing covers and head.

and you cant run the engine with the valve covers off, the engine would stall.

here's what rod knock sounds like:

http://www.youtube.com/watch?v=xNIbHUi7E7M

http://www.youtube.com/watch?v=niHvQ-P00gA

It's constant, not intermittent, and doesnt clunk like this one does.

It could be timing chain tensioner.

That sounds nothing like rod knock.
See above. Rod knock is cyclic and occurs at regular intervals, not randomly like in the video.
Stock cast pistons do not expand that much. Forged aftermarket pistons with high silicone content do.

That's defnitely NOT a rod knock...From watching the video, it almost sounds like intake backfire which I believe is sometimes caused by advancing the timing too much. Does it soundlike loud popping popcorn?? What is your base timing set at?? It's just a guess, so don't quote me on this...

I can almost promise you it's your timing, My car was making the same sound due to too much timing advance, the only difference was mine would idle okay but it made the noise when I would punch it. I just backed off the timing off a bit and it was fine. Try that out and see what happens:doublethu

but doesn't base ignition timing stay just about the same <2300 rpms? Why would the sound completely go away at 1000 rpms, with the nearly the same throttle position?

Man, that doesn't sound good. I "may" know what it is though. I did have that kinda noise for a week after my last year's motor swap. Then I fixed it and it was done.

Here's what I got...
With engine at idle, it clutters like that. Then when I pressed down the clutch pedal, the noise goes away. So, I thought it was tranny related. I took down the tranny and also found my flywheel snapped in two pieces inside the clutch assembly, they are just dangling inside the clutch assembly when the clutch is gripped onto the flywheel. When the clutch is not gripping, the noise got away. I did drive a whole week with the snapped flywheel and I even redlined it many times. You should try to see if clutch pedal down does make a difference, if it does, you may have the same thing I had. Mine was a stillen flywheel at the time, and it literally snapped in 2 pieces. Afterwhich, I replaced it with a fidanza flywheel and never had a problem with it at all.

-Peter-

it's automatic.

oh, sorry. then disregard my post.

Better give me credit freddy if it is... :wall:

UPDATE: I got some stp oil treatment, some thick synthetic oil, and 3 quarts of tranny fluid, seafoamed the car, and the sound is 90% GONE. I also replaced the FPR (this one was bad, didnt keep pressure at all, gonna have to get a new one)

I also think the alternator's not charging the battery, but i think I might have the wires crossed, or a fuse blown. Other than that, this car runs absolutely perfect. I ran the codes, and it's just regular stuff that's not gonna hinder the performance of the car. EVAP and EGR stuff.

That is good stuff. That noise was disturbing!