I've made other posts about this but nobody really takes it seriously. I've taken my car to mechanics, the dealership, transmission specialists... let me explain my problem
I'm driving in Manual mode in my 7AT g37 sedan. Downshift 7-6 manually just fine. Downshift 6-5 just fine. Then i go to downshift 5-4 and the rpms go up like its rev matching, it goes "braaaaat" cause my car has exhaust, but what feels like the transmission lags for 2 seconds, then jolts me hard in my seat. almost like i'm break checking someone. Only does it downshifting from 5-4 and i know its going to happen because ill feel the lag. its like this

*5th gear* brrrrrr
*downshift*
"braaaat"
.
.
.
.
*jerk*

it doesn't happen every time maybe only 1/15 times i downshift manually from 5th to 4th but its always only between 5th and 4th gear and never with any other gears.
i had shops look at it fluid was fine no codes nothing suspicious mechanic couldn't "recreate the problem" so they just sent me on my way but i want to put this CAI in and get it on the dyno so maybe i can go race some muscle cars in mexico but you know how stupid i look when i downshift my AUTOMATIC car and it almost looks like i'm driving a MANUAL BUT DONT KNOW HOW TO DRIVE A MANUAL. There's no way nobody has not had this problem before. Someone did tell me about a "tcm reflash" or something that the dealership can do for the transmission but when i asked the dealership they said "that was only for the earlier models" and my g is 2012

 

Is your ECM stock? Is your car a Sport?

Sport 7at came with a rev up feature upon downshifting. Sometimes when vehicles are tuned this feature is forgotten. It might be that only the Sports came with this, if so then a flash/tune should fix your issue.

 

it is a stock g37 sedan journey so it has the motor VQ37HR But it’s completely stock from the dealership

 

I don't mean to be insulting, but when you say you don't know how to drive a manual, you realize that when you downshift the RPMs will need to rise since you are going to a lower gear, right? The different in the gears will require the engine RPMs to rise to a point that they will match what the engine needs to turn in order to perform the downshift that you asked for. So, the question is: when you upshift from 4-5, how much does the RPM drop? Let's say it's 2,000 rpm. That means you cannot downshift from 5-4 until the RPMs are ~5K or less, or the transmission *will not allow you to downshift*. So you once in a blue moon delay and jerk could be because you asked the transmission to downshift and it cannot, so it has to wait for the car to slow until it can safely downshift, which then leaves you with a jerk and higher RPMs.

I'm not sure if that is your issue, but... be aware of what RPM you are running. Downshift when you need to. And no one with a manual downshifts when coming to a stop anyway, that's just pointless.

Good luck.


Rick

 

In a manual car unless it has some sort of feature to automatically rev match the gear you’re gonna have to hit the gas to match engine to transmission speed. No way you’re just clutching and going down gears without hitting the gas. My car is an auto so it shouldn’t need any gas to downshift if I want to go 5-4-3-2 at 45 mph it should do it easily. No stall no waiting for engine or transmission to catch up with one another because the computer is telling the car what to do I don’t have to do it myself. If I’m giving my car gas it just auto rev matches but if I’m not giving it gas then it’ll just lag do the weird hesitation for 3 seconds where the gas pedal tends to stop working and then jerk

 

This is correct, when I first flashed my vehicle the flash had the "rev up" option disabled and this is exactly what I experienced, a huge thunk as it forced the downshift without revving up.
This feature is a factory options in sport models, unsure about journeys. Unsure if a flash might enable it or not.

 

Tripps6x and Bull:

I agree with what you are saying about a feature to rev match and blipping, but my main point is that there is a mechanical connection between pistons and tires, in the end. When you a hitting the downshift button, if your RPMs in the current gear are too high for the transmission to allow the shift, it will ignore it. Depending on the tranny it may shift when it is safe, or just ignore it entirely. So my question to you is when this happens 7% of the time, what is the RPMs that you are turning in fifth, and how many RPMs would be gain after the shift? If you shift at >= 5000 rpm in 5th, I would not expect the shift to be allowed, since it would mechanically overrev the engine in 4th. In that case, I would expect the transmission to either ignore it entirely or shift when the RPMs dropped to 4000ish so then after the shift it'd end up in the ~6000 rpm range in fourth.

If you are ending up in high RPM after the shift ("braaaat") that would indicate you are trying to downshift at too high an RPM.

Good luck,


Rick

 

the rpm’s may be between 2500-3000 nowhere near redline I don’t daily my car in high rpm all the time but I do downshift myself because it helps when slowing down and taking corners harder when I need to but it’s usually low rpm when the car does this. G37 rev all the way to 7500 rpm so I should be able to shift down at 5000 rpm even if I wanted to but 5k rpm in 5th gear I would be going like 130 mph this happens at like 45 mph

 

I think it would help to see a video of this happening.

 

I wouldn't downshift above 5,000 rpm, since it literally makes no sense to spin the engine up to 7,500 because it sounds cool. Your brakes are designed to stop your car over and over, cheaply and safely. A whole set of rotors and pads are ~$500 or so. Your engine and transmission, on the other hand, are $10K plus. I suggest using the brakes. If I were to guess I think all of your engine braking has been wearing on your transmission, so I would change your driving habits or you'll have a repair sooner than later. Autos are expensive to fix and complicated.

I have been track driving for about 15 years, I understand all about braking and cornering. You downshift while braking (heel and toeing, for manuals) to make sure the engine is at the torque peak when you are ready to accelerate. The auto will do it for you. If you are using your engine to slow the car down, you are quite simply doing it wrong.

That said, if this only occurs here and there, buy a $100 OBD2 data logger that can record the last [x] hours and plug it into your car and leave it there. When the behavior occurs, pull the logger and check parameters to see what is going on. You probably want a full CAN-capable system and not just OBD2 since it won't dig deeply enough to help a lot.

Good luck,


Rick

 

Dude you take should be able to as a personal thing I didn’t say I do that and where did “spin the engine up cause it sounds cool” come from 🤣 I can’t help but feel like you don’t know about this car because the car engine breaks on its own while slowing down whether it’s in manual mode or automatic mode that’s what the rev up feature does this is just how g37 works. If I didn’t want to use the car for the features I wouldn’t of bought the car. Obviously I don’t engine break every time I slow down 🤣 I said when I take corners or break hard so I don’t know where that came from either. Do you even own a g or just browsing forums at 2 am I’m kind of 10 steps ahead of you if you read the very first post I made. Not even 3 mechanics or the dealership could figure out what’s wrong. A little obd logger wont do any justice. This car is a build it’s not that I’m worried to rebuild anything that’s exactly why I’m here trying to see if anyone has had the same problem because not even 3 mechanics or the dealership could figure out what’s wrong. My tuner did get back with me and say it will probably go away after all said and done and that’s a green check mark for me. He also said that the rev up feature is only from 1-4th gears because obviously you don’t need to have that in higher gears so it might be something as simple as a dirty MAF sensor so I’ll just drive my beat amg until I get it to him but for you to say all this and that taking what I said out of proportion is CRAZY 🥸🤓 I’m not even going to give it attention anymore

 

I’ll try to get a video if it happens tomorrow.

 

Hi Rick, you should inform yourself a bit more on this feature, it appears your info on this subject is limited and you're trying to comment from an overall mechanical experience. This feature is both a mechanical and electronic one. From the many times i've seen this it only a handful of times where it has neglected the downshift usually followed by a "beep" and the flashing of the gear, in other words the car saying "you can't". I have seen it downshift all the way to almost rev limit perfectly fine, during these experimentations it's "appeared" scary but many times is just my own opinion. The system is pretty intelligent and this itself has nothing to do with the problem the OP is facing.

So your car is tuned after all. You should have started this to begin with.
Either the Auto rev up feature is disabled or the line pressure settings have to be adjusted however the issue will be resolved only with the tuner. There is nothing you yourself can do on this other than fluid checking.
It is extremely important to include this for further diagnostics, tuned vehicles conduct themselves very differently than "completley stock" vehicles.

 

For the record, there is nothing wrong with using engine brake to slow the car down. You are right that it's added wear and tear on the drivetrain - but that's preferably to losing brakes entirely with continuous braking, such as when going down mountains. With rev matching - it shouldn't be an issue. I'd note that these ATs sometimes downshift, sometimes disconnects when slowing. Hard driving results in more wear & tear, too.

At high rpms, with no rev matching - your clutch is being worn away to equalize the differences between engine and wheel. I'd highly advise not doing this, at least regularly. A slipping AT can be expensive to get to and replace.

It sounds like the OP's issue is different - a video would let us understand the situation better.