Chris11LE

I wonder if Nissan is trying to get "lazy" and have the exact same shift setup for the tranny regardless of the engine its attached to. Probably a long shot considering this issue has been around before the G25 came about.

I still think they can get it right....if it really is a torque issue then maybe they just need to "tell" the tranny to hold a certain gear until its past this low-torque area in the powerband, or "tell" the tranny to downshift no matter what when you are on the gas in that same area. I think its more related to the torque converter not unlocking quickly enough, but again I would think they have the ability to program it out.........or at least make it better.

It really is a safety issue, the first time I experienced it I was coming to a left hand turn (no stop sign or traffic light), the person in front of me went and I went to follow....got on the gas and.....nothing, watched the tach flutter a bit and then got a downshift. Luckily I was expecting the downshift (thanks to this fourm) so I backed off the throttle at the right time, but had there been oncoming traffic close to me I coulda been in trouble. Its only a matter of time, unfortunately, before it might hurt someone.

Marc Collins

THAT is a problem...unless you have been coasting along and applying less than 5% throttle for a few minutes ahead of that occurrence.

Marc Collins

It's the shape of the curve from idle to 2,500 rpm that would be relevant. Are the 2.5 and 3.7 the same shape (ignore the absolute numbers). Does the 2.5 redline at 7,500 rpm (unusually high) like the 3.7? Is the torque the same percentage of HP at all rpms? I think the answer to all of these will be no.

moonsky

I know nothing about the 2.5L VQ. Part of your theory on the transmission problem is based on the claim that the 3.7L lacks low-end torque, requiring more downshifting and therefore causing more hesitation when the driver wants sudden acceleration by pressing hard on the pedal.

Here are the numbers, from reading dyno charts found online

G37 max 236 lb-ft (after drivetrain loss)
1500 rpm 175 lb-ft 74% of peak
2000 rpm 200 lb-ft 85% of peak
2500 rpm 220 lb-ft 93% of peak

I see that the VQ37VHR is not particularly lacking in low end torque relative to the peak torque. Yes, its max torque is low relative the max horsepower, but that's because horsepower is defined to be torque multiplied by rpm. The engine can maintain its torque output at a very high rpm, generating a lot of horsepower there. On the other hand, I think you are right on the throttle mapping part of your theory.

I believe torque converter is at least partly to blame. According to the company,

Would there be a delay introduced when handling a supposedly wide range of available lockup? Does the torque converter have to unlock every time the transmission shifts?

wpmcnamara

I can't say this from an engineering standpoint, only from real world observations. I came from a car without locking torque converter. Take you foot off the gas and watch the tach. With the torque converter unlocked, there is an immediate drop in RPM that represents the "slack" in the torque converter. On my G, when I take my foot off the gas, there is no change. It behaves just like a manual transmission in this regard.

And I don't think the torque converter unlocks on all shifts. The TC has two jobs. The first is obviously to allow you to start from a stand still without a manual clutch. The second is the important one for this discussion. The TC absorbs the difference in engine and transmission speeds immediately after a shift, smoothing the shift greatly and reducing the stress on the transmission clutches. For those that have drive and manual transmission, think about what it feels like when you abruptly pop the clutch in an upshift. Feel familiar? The car jerks briefly as the clutch plates slip until the engine RPM revs to match the new transmission shaft speed. Same thing will happen in the G during a rapid upshift with the torque converter locked. The rev matcher tries to smooth this out, but it can only do a certain amount in the couple hundred milliseconds it takes for the transmission to shift. The same happens in a downshift, but the feeling is different because of the relative forces involved.

I am also guessing that the torque converter is programmed to unlock if the shift will be more than one gear. This would likely be done because of the significant difference in engine and transmission speeds and to reduce the stress and wear on the transmission clutch. If the TC lockup is the standard fluid pressure type, then the solenoid valve has to close and the pressure drained off the lockup clutch to allow it to open. This obviously takes a non trivial amount of time and is probably required to be done prior to the transmission beginning the shift. This would certainly create a lag feeling in the shift.

I also have a sneaking suspicion that the drop in power that seems to accompany the shift lag is actually the ECU removing power from the engine to reduce the stress and slippage on the TC lockup clutch as it unlocks. This would definitely help with the lifespan of the lockup clutch, but make the car feel like it is loosing power as you press the pedal, just before it makes a major shift and takes off like a rocket.

See this link for an explanation of what might cause the shuddering in the 30-40mph range.

Almatti

The recent posts which supply real explanantions on the functions of TCs is fascinating to me. I'm getting a real automotive engineering lesson. But I have one question to very knowledge folks: why does the perfromance vary so much. To me I see changes one time, driving basically in the sa,e manner, and then different perfromance on another time, all things being equal. i know the discussions here and elswhere have always depicted that the TCM has a Logic - learning curve, that seems to adapt on a conastant basis. What is it adapting to anyway - what changes ?

sniper27

iTrader: (2)

I don't recall if this was answered already, and frankly, i don't want to go through 32 pages. lol. Does the 2011s come with the new program already?

wpmcnamara

I agree. The learning factor in this thread recently has been very high and very interesting. I hadn't bothered learning how a torque converter actually worked until moonsky's last post. Quite enlightening.

As far as the learning transmission goes I will answer the second part first. It is changing how it reacts to a given set of inputs and/or changes to inputs. This behavior would be the shift point RPMs, how many gears to upshift, when to lock unlock the torque converter and when to actually shift. I don't know that it actually modifies all those items, but those are the possibilities.

As far as what it monitors to learn from, it almost certainly monitors engine rpm, brake pedal pressure, throttle position, and throttle position change rate. It could also monitor lateral G forces, steering positions, wheel spin, O2 levels, temperature, even cabin occupancy. Some of these are obviously used for dynamic stability control, but I would be surprised if any of the latter set were actually used for transmission learning.

The transmission is trying to learn how to guess what you are going to need it to do without the benefit of being able read your mind or see through your eyes. For example. You just hit the brakes hard. Is that because an idiot just cut you off, or because you entered a tight turn on a curvy road? In the former, chances are, the car doesn't really have to do much quickly. After giving the guy the finger, you will probably gently press on the gas to accelerate where it will smoothly upshift and off you go. In the latter case, it needs to downshift, rev match, and me ready for you to stand on the gas to accelerate quickly out of the turn. How does it know what you need? It looks at your past history. If your past history shows lots of commuter traffic with stop and go and a few hard braking situations then you probably want it wait and smoothly shift. If your prior driving shows lots of hard braking followed by quick acceleration and lots of time spent in the max power band of the motor, then you are probably at the track or otherwise aggressively driving and it needs to aggressively shift. That is an extremely simplified explanation but it should give you a good picture of what it is trying to do.

It should also point out the problem. Most of us drive our cars as regular commuter cars in addition to whatever else we do with them. So the car learns our commute traffic and driving. Then suddenly, we get the opportunity to really drive the car. But the car is still guessing based on our daily commute. It can't see that the sun is out, it's 75 degrees and you have 30 miles of tightly curving road through mountain foothills and not another car to be seen, so you come into a turn, stand on the brakes, and it guess wrong and lags on the shift because it wasn't expecting you to hit the gas hard as your next action.

As I said, the above is a very simply example/explanation. I can tell you that the software to get the learning correct, or even close to correct is not simple and will always fall prey to drastic changing in driving behavior. The computer simply can't know enough to guess right. This is why some people state that in certain cases the car seems to be able to read their mind while in others it seems to have lost its.

This is a side effect of trying to make the car good at everything, which is another way to make it excellent at nothing.

wpmcnamara

Mine did, or seems to have and I got it at the end of February. May depend on the dealer and when they got their stock, etc.

Almatti

Cool, that's the description of Lagging.... The Torque Converter "feeling" for the lack of a better description is as follows:
when driving down a local street, say at 30-40 mph, RPMs at 1400-1500 or so, and I "feel" this slight, almost, rumble.....seems like its lumbering a bit. It is very reminiscent of the American Cars that I had when they first came out with OD - 4 speed Trannys..NOT THAT BAD, but close to that feeling. If you never drove those older vehicles, you won't know what I'm talking about, but you feel that slight Lumbering type of drive. Generally, in those driving scenarios, not at highway speeds. In fact, I never test drove the car like that in June, but noticed right away on the drive home after I just picked up the car new....I said to myself: "WTF"...The Reflash helped the quirky coasts to a stop which were terrible, but not too much else for me. It just WILL NOT BE THE 07 G35X that I had.

Almatti

wpn, very well said....I like the part about: "giving the guy {or Gal} the finger"....LOL...Can you offer some further explanation on how the DS mode may have been affected. It is different : from my 07 with a 5AT, and it too seems to adjust and react differently consistent with the previous statements about the constant Learning Curve of this TCM.

Another member who has posted here frequently - "Fish"... has posted that he has reset his ECU (using the method posted much earlier on this thread of doing it with the throttle [pumping 5 times, etc]) a number of times after his car has "learned" an undesirable driving scheme. In your opinion, is that necessary? Should you actually do that so regularly?? Can you reset the ECU, then drive the car like a Banchi to produce sporty - aggressive programming? Thanks for your input. MarcCollins, you too... fascinating material...

I will say, we have come a long way from 4 barrel carburetors, changing the "points' in distributors, setting gaps in spark plugs, setting the Timing with Timing light, etc...WOW.

wpmcnamara

Not sure how D vs DS would come into play. In may last car, a 2002 BMW 330i, DS was designed to hold the shift points till much much higher in the rev band and would shift till red line if you were really on the gas. Upshifts were also much more aggressive. It was set so that it would upshift to keep the revs in the maximum torque part of the RPM band as you slowed. This produced something similar to the engine braking on the G and meant that if you hit the brakes hard then stood on it in DS mode, you could give yourself pretty good whiplash at 20-30mph. However in the 330i, all the shift points, etc, were fixed.

Based on reading the manual and driving the G, it would appear that D vs DS starts out similar, DS having an agressive shift map and D having a smoother one. If I were writing the learning system, in DS I would give priority to inputs that tended towards sporty driving, while in D mode, normal stop and go/highway cruise type driving would be favored. However I have no way to know what the engineers did. It is entirely possible that the learning system can effectively override the default shift program to the point where D and DS drive exactly the same.

Resetting the ECU/Transmission computer should clear the learned behavior out of the system and return it to the default shift maps. It should then start re-learning your driving pattern. If you reset, then drive in an aggressive manor, it should learn that and perform well in that mode. Of course, then it is going to feel rough in stop and go traffic as it will be trying to do performance shifts when it shouldn't be.

The other big question is how quickly does it learn? Is my wife driving it for a couple of days sufficient to undo the "sport" learning it has done over the last week? Is a week of normal commuter driving enough to undo it? That we don't know, and may never really.

Resetting the ECU isn't going to hurt the car really. It may change your mileage, and will almost certainly change the behavior of the transmission. If you don't like the way it is driving now, do the reset and see what happens. The worst that will happen is that it will re-learn the exact same driving pattern that it has now.

burningembers

So could I solve some of my sticky around-the-town shifts in D-mode by doing my highway commutes in DS? Does it keep separate "learned" profiles for each?

wpmcnamara

The service manual doesn't mention anything about different learning profiles for D and DS modes.

Reading the service manual, the car does appear to monitor G forces and wheel spin for shift control as well stability control. Almost makes me want to go get a Consult III unit just to see what the car really thinks is going on. The service manual clears some things up and makes others about as clear as mud.

My thought would be to stay out of DS mode unless the driving you are doing is what you consider "sport driving". I don't consider 50-70mph highway cruise sport driving, nor do I consider stop and go traffic, sport driving. For me, sport driving is a road course, or twisty back roads with no traffic. There are very few times I put it in DS during my normal course of driving. I just use the paddles when needed. Even in regular D, you can override the shift points (as far as the car will let you) by using the paddle shifters. If you are in traffic and are about to have to make a quick lane/speed change to merge with traffic, use the paddles. You know way better than the car ever can what you are about to do, so drive it like you would a manual. Just before the merge, upshift, then hit the gas.

After reading the service manual and all the other technical stuff I have over the last couple of days, I am pretty sure that almost all the problems could be fixed in software. However, doing so would probably significantly drop the mpg rating, shorten the life of the transmission somewhat, and probably not appeal to anyone who buys and Infiniti because it is a luxury car. Reducing or removing torque converter lockup at all but highway cruise would help, and would removing or significantly delaying the tendency to aggressively shift to the highest gear when the throttle position is static and the car is not accelerating. Both of those are mileage related features. My thought would be to leave them in D, but remove them in DS.

I think they tried to make the transmission too smart and be everything for everybody.

burningembers

Guess the real answer for me is to do an after-market paddle shift install since I don't have paddles, and just shift how I want to shift when necessary

I also noticed I can pretty much eliminate shift lag around curves/turns between 20-30mph by pushing the pedal in about 3x more than I would expect I need to. If I do this really fast, then settle back to my normal depth, it doesn't search at all and off I go. This will suffice...now I just need to figure out how to keep it from searching so much in stop-and-go traffic at about 25mph.