So I've always noticed that when cold starting the Q it makes a fairly pronounced rattle/knock noise for the first 10-15 seconds then goes away. Anyone have any insight to what that is or have the same noise? I remember on the G37 similar cold start sounds but the Q's is soooo much more noticeable because after that initial 15 second window its absolutely gone and sounds wonderful. I've theorized that it's the timing chain but why would it make that rattling sound for 15 seconds then turn off like a switch. It's too clean of a stop in sound to be because of heat buildup, the cutoff sounds intentional almost.
Cold Start Engine Rattle Noise
LoganB
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Yep, absolutely correct. Just when the rpm's surge a bit and settle back down, the cold start up process is complete. I'm told by an Infiniti tech this is done on purpose to heat up either the turbos, wastegate, motor, or all of those (can't remember exactly what he said), but it is in fact part of the normal cold start process. I'll ask him to remind me again as I forgot the details of what exactly causes the noise, but it's definitely by design during cold start to quickly heat up one or all of those components to operating temp.
Pretty sure it's to let the engine warm before the turbos come into play. The exhaust is louder because the tubos (which act as mufflers) are bypassed. The exhaust is routed around them instead of through them to help protect a cold engine.
The high revs at cold start is for emissions. CATs are not fully effective until they are up to a high temp (~800 degrees). The engine is set to idle at higher RPMs for a few seconds to get the CATs up to temp quicker, preventing fewer emissions from entering the atmosphere.
This is why this happens on both Gs and Qs.
This is why this happens on both Gs and Qs.
Revs are still "high" after 25 seconds however, the exhaust decibels drop dramatically. (Infiniti Sport Exhaust Kit)
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It's definitely a rattling can sound. I didn't get a chance to ask one of the techs today, but he did explain it to me, I just wish I could remember.
My '17 Q60RS is at dealer getting an issue addressed and they gave me a 2019 base 3.0t Q60 as a loaner and I don't hear the same rattle. Actually there's no rattle at all during cold start.
I'm curious to find out if something chaned with the cold start process for the later models, or if not, maybe the earlier models all just have noisy cats and/or heat shields during cold start and they addressed that in the later models.
Regardless, the rattling doesn't seem to be an issue other than sounding bad for the first 15 sec or so...and maybe a bit embarrassing for some on a $50k+ vehicle. I cringe every time I hear it...can't help it, it just sounds so...well, cheap and crappy... lol
My '17 Q60RS is at dealer getting an issue addressed and they gave me a 2019 base 3.0t Q60 as a loaner and I don't hear the same rattle. Actually there's no rattle at all during cold start.
I'm curious to find out if something chaned with the cold start process for the later models, or if not, maybe the earlier models all just have noisy cats and/or heat shields during cold start and they addressed that in the later models.
Regardless, the rattling doesn't seem to be an issue other than sounding bad for the first 15 sec or so...and maybe a bit embarrassing for some on a $50k+ vehicle. I cringe every time I hear it...can't help it, it just sounds so...well, cheap and crappy... lol
I removed the heat shields. Since I have the Infiniti Sport Exhaust Kit my exhaust is loud AF for about 25 seconds and then "calms down". I have no rattle.
I hear a rattling on cold starts as well. For me it appears to be coming from the front of the car though. I recall reading somewhere that it had something to do with the direct injection system testing itself at startup. I could be entirely wrong though.
Maybe my exhaust is just too loud to hear it :laugh:
I forget, is yours the straight pipe or the helmholtz one? I can hear the noise over my helmholtz exhaust kit.
To quote Shaun Tee from the VR30 Tech Group:
nitially the wastegates are fully open at startup (8mm position), and then suddenly fully close before settling into an intermediate position (4mm) for about 30 seconds, and then fully open again.
What you're probably seeing is Nissan ensuring sufficient exhaust pressure to light up the catalyst for cold start emissions. As things settle down, then the wastegates are fully open again and the turbos die down back to idle.
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The Infiniti Sport Exhaust Kit is a pair of straight pipes >
In that graph, is that fat green line indicating that turbo speed that drops off around 29 seconds (on that scale from a 3 to a 1)?
I think you mean the dirty yellow line, but yes. I don't know if that's a stock setting, because the graph is from an ecutek log. I believe the turbos are set to spin at 10krpm at a minimum.
To h-e-l-l with that log. IMO for the first 25 seconds of a cold start, exhaust gasses are bypassing the turbos and going straight out the pipes. That's why my Q60 is loud AF during that time.
Not sure why you're upset with the log. Turbos spin at idle...also the wastegate is only fully open for a second before it goes to half open. Also, a loud cold start is from the richer fuel mixture determined by the ECU until the cylinders are up to operating temp and can vaporize the fuel more readily.
I'm not implying that they don't spin. Feel free to explain why my stock Q60 RS (except for the Infiniti Sport Exhaust Kit) is loud AF during the first 25 seconds of a cold start. I don't put the car in gear for a full 2 minutes after starting. Pretty sure the turbos spin when I pull out of the driveway, but the exhaust is not nearly as loud then.
With a cold start, the engine is cold and will not readily burn fuel as readily as a hot engine. To prevent stalling, the ECU commands a richer fuel mixture and a higher engine speed to make sure all the excess fuel is forced out of the cylinders.
I own two superbikes with EFI and richer fuel mixture at start, but they're not any louder at cold start than they are at warm idle. Every vehicle since the 1960's has a rich fuel mixture at cold start. The Q60 acts different.
The RPM on my Q60 is no different at 30 seconds after a cold start than it is at 25 seconds, but the exhaust loudness is considerably different. Again, both my superbikes have EFI, one has an Akrapovic open exhaust.
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