throttle lift off lag
 

i've noticed in my car ever since i got it that when i lift off the throttle, there is about half a second lag time during which the engine maintains current rpm before dropping off to idle. doesn't matter if the car is in gear or neutral or if srm is on or off. what causes this? is it the electric throttle being slow to respond?

Try turning off SRM to see if it makes a difference. SRM holds revs in between shifts to anticipate gear changes.

like i said, i already tried that. its not srm. its not that the engine is held at a certain rpm, its more that there is around half a second lag time after i lift off the throttle before the engine revs down to idle.

:iagree:

Here's a great video that explains the upshift



BTW, this is NOT me :icon17: . Some kid on youtube.

EDIT: I guess we posted at the same time. That's weird. Hopefully someone with the same issue will chime in.

lol neither of you 2 read what he said.. he already tried turning off SRM... mine doesnt have SRM and it does the same thing. Probably has to do partly with the extremely heavy stock flywheel

or just a fuel map to burn off the last bit of fuel for emmissions control...

It's the heavy flywheel. More mass = more rotational inertia. That's why lightweight flywheels are a somewhat popular mod for Zs. The 350 was the same way. Nissan chose a heavy flywheel out of noise considerations.

Does Nissan use a DBW or is it a Cable? DBW lag sucks ballz:shakes head:

Interesting... I never really recalled the 350Z holding revs in between shifts. Revs dropping slow wouldn't surprise me, but there has been some discussion in regards to the 370Z holding revs while shifting. It took awhile for me to get used to this behavior.

sometimes, especially skipping a gear this leads to a "lurch"

wire. i agree it could be dbw lag. also the part about buring off the remaining fuel does seem to make sense. i highly doubt the heavy flywheel is the cause. a heavy flywheel would mean a slow rev down. what i notice is more that the engine rpm stays put without slowing down at all for about half a second or so, before beginning to slow down. the lag also seems to be independent of rpm. it's about the same duration whether at high or low rpm. if it was the flywheel, there would be more lag at high rpm and less at low rpm.

for those who say srm, no, actually the car doesn't even have to be in gear or even moving for this to happen. just try this. leave the car in neutral. push the throttle and hold the engine at a constant rpm, doesn't matter high or low. keep your eye on the tachometer needle, and immediately lift off completely. you should notice a small delay between the moment the throttle pedal is lifted and the moment the needle begins to drop.

also can someone with the automatic also try it just to see if it is indeed the flywheel or the electric throttle

yeah, it's definitely noticeable if you upshift really quickly and immediately let out the clutch. the lag makes the engine maintain too many revs and can cause fast upshifts to be very harsh

Ooohhh....I think I misread your original post. You're not disengaging the clutch, are you? You're talking about a situation where you simply lift off the throttle but you're still in gear?

circuitry lag

drive by wire

:iagree:

That, and general lack of F-L-A-W-L-E-S-S-N-E-S-S. ;)

obviously the car is not in gear, or if its in gear the clutch is disengaged and srm is off. yeah it does seem like circuitry lag due to the electric throttle. all my previous cars had mechanical throttle cables, and throttle response was definitely much more immediate both in opening and closing the throttle

My other car does the slow Rpm drop. In researching, it was for emmission purposes.
The unit is called a decel-valve.


Disclaimer: this may not apply to our Zs

I've wondered if this does anything to help:

Sprint Booster USA - MT

Seems like it just increases throttle sensitivity on acceleration. No one online really comments on how it would address the issue in this thread. I may go locally and try one out as a demo (offered on their website)

I doubt its circuitry lag - maybe a delay built into the software but not a hardware delay.... these ECU's are very capable.

:iagree:

I notice it as well. If there is a delay, it is programmed for a reason. Electronics are as fast as a cable.

That's a popular mod over at MB World. The throttle on the V8 Mercedes are tuned for seniors, so you have to push the pedal 50% to get maybe 15% throttle. :icon17:

Wow, Nissan did something to quiet the noisy engine? Pity they didn't do more.....................:icon17:

Agreed. Unless this 'alleged' issue is hard coded into the circuitry. I tried this on my car and could not replicate.

If your car is not in gear when you lift off the throttle, then I stand by my belief that it's related to the high-mass flywheel. The fact that it hangs for a second before it drops is consistent with what I'd expect from a flywheel with a lot of rotational inertia. But hey, who knows for sure, right? Heck, maybe it's not just one factor. Maybe it's a combination of factors (i.e., heavy flywheel combined with DBW).

Still waiting for someone to comment on the Sprint Boost thing...

Huh?

7AT does it too - when I brought my Z home, I nearly launched it through my garage, as I was carefully/slowly pulling in, and got "stuck" on the 1.5" bump where my garage door sill is.

I blipped the throttle, the BOLTED forward, I slammed on the brakes, and managed to not park my Z in my second bathroom.

Ditto... I think it's a feature of some sort as I have noticed this behavior test driving the 7AT. The 350Z didn't do that, so it shouldn't have anything to do with the flywheel holding the revs.

My other car does it too... Especially the one with ULEV. I don't think it has to do with the flywheel. throttle just hangs momentarily to burn off fuel.

Once you get use to it though you'll learn to time urself for the shift and it won't bother you. Since my other car hangs worse (and is a MT) the Z never bothered me at all. :p

If the 7AT does this as well, then I agree that it's most likely an electronic 'feature'.

it is probably for emissions purposes i could see that.. the car hangs even worse when the car isnt warmed up. on a cool morning start your car up wait 30 seconds or so drive off and take a look at everytime you shift it will hang longer and even rev up slightly everytime you shift when its not warmed up.

not necessarily for emissions, but the ECU holding the RPMs to make sure the fuel is burnt and such makes perfect sense.

Here's my take: It is the modern, electronic equivalent of the old decel controls on carbureted engines. Meant to control emissions on deceleration when throttle is fully closed.

US Patent 3957022 - Carburetor deceleration emission control



Description

This relates in general to a two-stage motor vehicle-type carburetor. More particularly, it relates to one that is provided with suitable apparatus for cracking open the secondary induction passage throttle valve during engine deceleration conditions to improveemission output.

This invention has particular use with four barrel truck-type carburetors, although it will be clear that it will apply equally as well to any carburetor having dual stage operation. In a four barrel carburetor of the type describedhereinbefore, the conventional idle provides a quite lean mixture to the engine cylinders. During closed throttle deceleration operation, therefore, the engine will be provided with a very lean mixture to the point where incomplete burning mayoccur, which may result in unburned exhaust gases and the emission of undesirable into the atmosphere. If, during this time, fuel and air is added to supplement the idle system mixture, then a more complete burning of the mixture may occur. The addition of fuel alone generally is not sufficient but both fuel and air should be added to provide the proper mixture ratio.

Accordingly, it is a primary object of this invention to provide an engine deceleration control apparatus incorporated in the carburetor that operates during deceleration conditions when the primary and secondary carburetor throttle valves areessentially closed to crack open the secondary induction passage throttle valve to supply a quantity of both fuel and air mixture to the engine to supplement that mixture emanating from the primary induction passage.

It is another object of the invention to provide a four barrel carburetor with a vacuum servo connected to the secondary induction passage throttle valve and operable during predetermined deceleration conditions to crack open thesecondary throttle valve to allow the induction of an additional air/fuel mixture into the engine.

It is a still further object of the invention to provide a four barrel carburetor construction having a servo operated secondary throttle valve system with an additional vacuum servo that is independently operable during predetermined enginedeceleration operating conditions to crack open the secondary throttle valve to allow the addition of air and fuel to the engine regardless of the position of the primary throttle valve and quantity of flow of mixture through the primary inductionpassage.

It is another object of the invention to provide a four barrel carburetor construction having primary and secondary induction passages each provided with a separate throttle valve rotatably mounted across the respective passages to control theflow of an air/fuel mixture therethrough to the engine cylinders, the secondary throttle valve being opened to provide greater air flow capacity to the engine during engine acceleration conditions by means of a vacuum servo connected to the throttlevalve and operated in response to a vacuum signal in the primary induction passage venturi at the appropriate time, an additional vacuum servo being connected to the secondary throttle valve by a lost motion connection and operable in response to theattainment of both a predetermined engine speed and vacuum level condition to crack open the secondary throttle valve to permit the induction of an air/fuel mixture through the secondary passage to supplement that flow quantity being supplied to theengine by the primary carburetor section, to render the engine air/fuel mixture burning more complete and thereby reduce the output of harmful emissions.

It is a still further object of the invention to provide a carburetor of the construction as described immediately above in which the second servo is actuated by vacuum as controlled by a solonoid actuated valve that iselectrically actuated in response to engine speed and manifold vacuum both rising above a predetermined level.

Carburetor deceleration emission control - US Patent 3957022 Description

^ Good info. +rep

Lmao I was eating lunch and reading through the whole thread and your last paragraph almost made me spit out all the food in my mouth. :) and yeah I definitly do feel a throttle delay compared to my g35c. I can slam the accelerator down and there's a heavy delay. The g35 was very sensitive. I loved it.

We're not talking about a throttle delay :ugh2: Is your G35 a 2004.5 model?

:facepalm:

I know you guys are talking about the throttles rpms hesitating to go down once you let go of the accelerator but didn't someone also mention about the accelerator being delayed also? I might just be going crazy lol but my g was a 2003.

Yep this was one of the first things I noticed when I first got my 350. I think its by design. The reason I say that is because in all my previous cars, if I was rolling on 1st gear and then dropped the pedal it would jerk back and forth. But in the 350 you could roll in any range of 1st and drop the pedal and experience little o no jerking. I think it was designed to allow for a smoother ride when dropping the gas pedal at high rpms.