What's this "clacking" noise?
 

Under hard acceleration and under boost, I hear a brief ratcheting or clacking noise in the engine or drivetrain when I abruptly take my foot off the pedal. I can easily reproduce this when I accelerate hard to about 4-5k RPM and quickly take my foot off the pedal.

It is similar to the brief clacking noise heard on some of the VQ37s on an engine start, which I also hear sometimes.

Since you have boost, I assume you have tweaked the fuel injection. My first guess is that you are not stopping fuel flow fast enough, you're getting unburnt fuel into the exhaust system, and you are hearing muffled explosions. But that's just a guess.

I've heard exhaust popping noises, but it sounds like valvetrain noise.

Backfire and what OP is claiming is 2 totally different noises.
Sure is funny to hear that under hard acceleration. Can't really guess the problem other than sumthin moving while under load. If its happening around 4-5k rpm I'm sure that's where ur torque peaks at and that's not good to hear that noise at that moment. Good luck getting it figured out!

Thanks, I don't hear it under moderate acceleration or when I ease up on the pedal.

Oh, what's also interesting is when I'm in the higher gears when pushing the motor and abruptly taking my foot off the pedal at low revs like < 4k RPM. I can hear this noise, so it doesn't have to be in the lower gears.

[EDIT] I remember now. I was testing for clutch slippage by briefly flooring it in high gear 3-4k RPM around 40 mph.

could be your rear axles clicking. mine are doing it during acceleration and deceleration.

Do you have a vid of the noise.?

Do you hear the metallic clacking sound on startup? Some G owners reported this as well. It's a similar sound. Just push it a little hard in the high gears and abruptly let off the throttle.

Hey fuct I also hear my rear axels clicking upon acceleration and deceleration show i be worried and take it in for service? Or are these noises common for the Z?

wait........you don't transport chickens in your car, do you?

clacking != clucking

I had the same noise - took it into the dealer, and the service manger says it's a very common problem. The rear axles need to be removed, regreased, then retorqued. You should have no issues if you have a warranty with the car or anything. They took my car no questions asked, and I was done in an hour or so.

I'm hearing the clunking noise, which is referenced in my other thread. I have to get it checked on my next oil change.

Cool thanks for the info! I do have warranty on my car so on my next
Oil change I'll ask them to check it out.

u joints, flexplate/flywheel loose or diff bushing, would be my guess.
I had this issue, only in first gear.. ended up to be my u joint in the rear.

You may want to stay out of boost and get the tune checked. It could very well be detonation in that certain RPM range.

Prolonged detonation will put a hurting on the rod bearings and they'll eventually give out.

Running on GTM's base tune. I sent in logs several months ago and never got a response.

I had the car on the dyno a couple of times and the AFRs are good. It is pretty rich. Plus this noose only happens when I let off the throttle abruptly from at least half throttle in higher gear. It doesn't do it otherwise.

This was a common problem on the 350z's ,it happend to me on my 350z so far so good on my 370z.

Ahh, base tune is all you had to say :)

I hope you get it figured out.

Jus to be completely safe if I were you I'd get a custom tune so that it can be on the money. No need to run extra rich when a tuner can dial it in n make it run smoother.

Sam's tunes are normally spot on at wide open throttle with the air / fuel numbers. 450whp is conservative, but not all gas is created equal. Running too much timing on a canned tune could turn fatal if the tuner isn't able to watch all that is going on.

Where are your numbers around? 11.1 - 11.5 a/f at wide open?

At wot I'm around 11.2.
Still regardless a generic tune doesnt compare to custom. Altitude, gas, humidity, weather in ur particular state/city you live in plays a factor. When I mean by custom tune u should look for a reputable shop close to you not jus anybody. In the end was worth it for me. I was running really rich but I'm sure Sam does that for the extra safety, but again there was no need to run that rich (well me personally).
At least get it on a dyno n have a competent tuner check it all out.

For sure man

Yea, the AFRs are in the low 11s to redline. If you look at my dyno charts, there's no oddities. Curve is smooth. One of my friends test drove it yesterday since it was nice can "cold" out (no worries about power drop). It runs great all the way to ~8-9 PSI. TCS keeps kicking in even in 4th! Haha. Once he felt comfortable, he turned it off and handled the car as it got squirrelly under boost. He says it felt scary, but it was quite fun. This is coming from a Lotus owner :)

Right now I'm still on the fence: Continue with cooling and exhaust upgrades to the final tune of about 500 whp or sell and build up an NSX (depends on job situation as well). I'm pretty sure the new throttle map and VVEL tune will spice things up and make the car even more fun to drive and make me forget about wanting an NSX.

Ah... here's the post from another forum (hopefully not blocked)
MyG37 - View Single Post - klonking noise on start up.

See if you can download this MP3 file. This is the same noise I hear on engine start. Unfortunately, this is something I heard every so often before the turbos were installed. At the time I could not find any answers whether this was a serious engine issue or not.

This is a similar noise when abruptly taking foot off the throttle given a decent amount of load in the higher gears like 6th. This is something I've not done lately because I was testing for slippage in 6th at 40 MPH.

I've looked up other videos about rod knocking, and it is a similar sound. Yet, my car runs and sounds fine at with normal or hard driving (other than the test mentioned above). The noise isn't there at idle (very frightening when watching some of the videos on YouTube).

OMG, from G37 Forum someone posted a thread here from Daishi! Haha...
http://www.the370z.com/engine-drivet...k-startup.html

Manual? Might be a your throwout bearing. One of the arms could have bent perhaps, or even broken off. I did that with my 97 Type R Integra...several times. Similar 'clanking' until I did a clutch/flywheel replacement and saw the bearing shot to hell. The bearing housing was in the place it should be, but not seated because of the broken arm and would rattle upon acceleration and engine braking.

Put the car in neutral, then slowly rev it all the way up. Then come down slow on the accelerator. Is the noise present?
Still in neutral, rev up quick, hold for 5 secs, then come off it fast. Any noise?
If yes, you might have a serious issue. If no, start looking under the carriage for rocks between rotor guards, worn cv's, then you might have to open the transmission and look at the bearing.

The honda trans had a bearing with two 'hook' arms. One broke off, and the noise was the only indication; no difficulty shifting, no 'grinding noise' etc.

Best of luck!

Thanks for the suggestion. There's a dust cover under the transmission so one can peek at the CSC bearing. It's fine for normal or aggressive driving other than abruptly taking foot off the gas under heavy load at low speeds. I honestly haven't performed the 6th gear clutch slip test for the past several months since getting a new transmission (prior, new clutch disk).

One more for thought...

Check your trany and differential mounts. One may be split and allowing those parts to knock against the frame.

Thanks. I'm going to get those inspected very soon. Lately the car shakes from juddering whenever I go in reverse. I have to feather carefully or the car shakes violently. It happened before when the car was new, and it started happening again even with an aftermarket clutch. It comes and goes.

Bringing this thread back... I'm hearing this fast "clacking" noise every once in awhile in 1st at low RPM as I get the car moving. It's just casual acceleration. It sounds like a machine gun "clack-clack-clack" sound, and it's brief. The car doesn't judder, so it's smooth.

Earlier I wrote that this sound can be heard if I briefly hold the throttle down in 6th at low speed around 40 MPH, and quickly lift the throttle. It's the same sound, but now I'm intermittently hearing it in 1st at low speed.

I can almost bet that's the throw out bearing

Sure hope so... I can confirm the Southbend clutch/flywheel combo is quite noisy at low speeds especially around 1,500 RPM. So this noise is definitely low RPM. I just have a habit of getting the car moving around 1-1.5k RPM (light throttle, of course).

Oil pressure is close to 30 PSI when I get it going in 1st. At idle, the lowest is around 20-25 PSI. There's almost 1,500 miles since the last oil change.

That's just clutch/FW noise man...

Even with the stock dual mass crap, I hear it from time to time.

Try and get a video of it if possible... The description is vague through the internet and it could be many things. Sounds a lot like some normal sounds, sounds like some not good things... Depends on if I'm being an optimist or a pessimist

See if you can download these files:
http://www.myg37.com/forums/2501490-post14.html

This is the "clacking" noise on startup on a G37, which I also get. It's the same sound. It's not a "ticking" noise either.

What's scary is the repetition and speed of the noise sounds like a rod. So far I've heard it a couple of times at low speed in 1st. Haven't heard it anywhere else, unless it's only the beginning. O_o

I'll try to get a recording whenever I have time.

I have a similar noise with light throttle between 2500 and 3000rpm on mine. It goes away in neutral or with the clutch in, so I'm doubting that it's motor related. It also started right after the turbo kit was installed with a new clutch and lighter flywheel.

The transmissions make all kinds of noises in these cars but they sound nothing like engine noises. The trans sounds are best describe as a cement mixer or grinder. It literally sounds like the transmission is full of rocks. That is normal when you load the trans at lower rpm or even at idle.

Engine sounds are very different. I can't process those zip files from my iPad here so ill try again later. If it makes a valvetrain type of sound on startup and only startup, I would first think maybe a timing chain tensioner was leaking pressure. If it does it all the time the engine is running at specific rpms and load, I would get a little more worried.

Make sure you don't have any of your DTCs disabled that would be related to cam sensors, cam timing, etc.. That way if its related to the VTC it might show a code. I've seen really noisy VTC gears in a DE before.

Does it do it more or less when cold or hot?

If we cannot Internet diagnose it, I would run it by a performance shop that is known for engine work and see if they will come out and listen to it. I would hate to make you paranoid over nothing... But it's just that if there is a serious issue, it's so much better to just stop before something actually lets go and takes out a bunch of expensive parts with it.

I'm convinced this is my issue, and it probably occurs at higher rpm as well but the exhaust drowns it out. It is more noticable when the car is warm, and my wild *** guess is that the lube in the tranny is thick enough when the car's cold to quiet it down.

No problem. I just went out to check the oil level, which is still over the halfway mark. Looks like it needs a new drive belt, though. I saw a couple of spots where it's fraying.

I started up the car while it's 86F out in the parking lot. No weird noise (no clanking noise on start up either), lightly revved it up a little to about 3k rpm, nothing unusual. Oil pressure is around 40-60 PSI while warming up.

The only times I can remember hearing this noise is at low speed like cruising in the neighborhood in 4th or 5th. This morning, it was when I was making a left turn. The noise was brief as I feathered the clutch out to get the car moving, and that was it.

that post sounds a lot like the transmission sound. if anything, perhaps familiarize yourself with the transmission sound by inducing it intentionally.

with all fluids up to normal temp, put the car in 4th or 5th gear, get down to around 1900 RPM. with windows down and no background noise, give it 3/4 throttle or more for a few hundred RPM... you will hear that sucker roar.