Nissan Murano Forum banner

1 - 16 of 16 Posts

·
Newbie
Joined
·
101 Posts
Discussion Starter #1
Here's one to try. I was waiting at a stop light and put the MO in neutral while I fiddled with the CD player. When the light turned green, I abruptly dropped the shifter into drive and hit the gas (pretty hard since I didn't catch the green light right away and got beeped). Nothing....no burst of acceleration and barely any pick-up whatsoever!! Instead the transmission slowly came up to speed and I veerrryyy slowly pulled away. I thought I was imagining things, so I tried it again with the same results.

I figured shifting from N to D and then hitting the gas immediately did not give the computer controlling the trans/engine enough time to 'think', which caused the lag. It's just that the lag was so bad!

My wife's car has an automatic and has the off-the-line lag all automatics have (the MO is no exception), but her car does not have this severe a problem (when shifting from N to D then accelerating).

This problem does not happen when the MO is left in D and then accelerated. Any one else ever experience this?
 

·
Registered
Joined
·
3,285 Posts
"This problem does not happen when the MO is left in D and then accelerated. Any one else ever experience this?"

No. This is one of many things I have never tried.

Worst thing I have ever done along this line was put the E brake on and turned to get some stuff out of thr back seat of a rental car. Car was still in drive.
So when the guy behind me blasted his horn I spun around, gave it the gas, and didn't go anywhere!
And it all got worse. I couldn't remember that the brake was on for 5 or 10 seconds.:rolleyes:
It had, like the Murano, the dumb foot actuated brake that you can't see..........I hate these foot operated brakes. Makes me feel like....... that although I am really driving a Nissan "Sporty Car", it is cleverly disguised as a 1956 Buick.:15:
And they are no good if you really need them in an Emergency situation.
Maybe these are more properly called "parking brakes" and the hand operated ones are emergency brakes.
In any event, since I have driven "mostly" real cars and very few mushmobiles, I'm not very used to them.

Might I suggest you leave the car in D next time and at least try putting the brake on..........

Homer
 

·
hail 2 the snail
Joined
·
796 Posts
stonemaster said:
Here's one to try. I was waiting at a stop light and put the MO in neutral while I fiddled with the CD player. When the light turned green, I abruptly dropped the shifter into drive and hit the gas (pretty hard since I didn't catch the green light right away and got beeped). Nothing....no burst of acceleration and barely any pick-up whatsoever!! Instead the transmission slowly came up to speed and I veerrryyy slowly pulled away. I thought I was imagining things, so I tried it again with the same results.

I figured shifting from N to D and then hitting the gas immediately did not give the computer controlling the trans/engine enough time to 'think', which caused the lag. It's just that the lag was so bad!

My wife's car has an automatic and has the off-the-line lag all automatics have (the MO is no exception), but her car does not have this severe a problem (when shifting from N to D then accelerating).

This problem does not happen when the MO is left in D and then accelerated. Any one else ever experience this?

when i FIRST bought mine, i felt the 'lag' too....

it must be a inherint with the CVT setup...... and it onmly occurs on the initial shift from P to D...... but now that i have driven her for a month, i am used to it, and it goes un-noticed mostly.....

maybe a centrifugal blower will compensate some......... hmmmmm we'll see??
 

·
Newbie
Joined
·
101 Posts
Discussion Starter #4
I drove sports cars all my life (manual transmissions) and I am used to putting the car in neutral at a stop. I still do that with automatics because I don't want the car to sneak forward should my foot come off the brake (and only if I'm stopped for any long length of time or if I need to take my eyes off the road for a few seconds while stopped).

If you shift back to D from N(eutral) a few seconds before accelerating, there is no hesitation effect. That's what I've been doing and haven't had a problem.
 

·
Registered
Joined
·
34 Posts
Definitely noticed this type of behavior and frankly at the worst time. My experience was a little different than Stonemaster's however. I was accelerating through an intersection in a turn lane, hit uneven pavement where the road was being repaved and hit the shift lever(I frequently rest my hand on it). It dropped into Neutral and although I almost instantly popped it back into Drive the car rolled slowly with almost no drive power through the rest of the intersection(with oncoming traffic!). It took several very long seconds to recover and begin moving and as I was now pushing the accelerator harder it only seemed to make the effect worse. I actually thought I'd stalled the car as the engine is relatively quiet and it had absolutely no power.

I've since tried it almost exactly as Stonemaster described and found that revving while trying to accelerate quickly only makes the situation worse. If you begin to accelerate, drop it in Neutral, drop it back into drive, and hit the gas, you'll probably see the same behavior(ie. it's not just when shifting from Park to Drive). I think it's potentially hazardous should you find yourself in a situation where you have to quickly accelerate out of Park or Neutral, whether intentionally or by accident. As I routinely mash the accelerator in all three ranges and the engine/tranny response is phenomenal, this really is unexpected behavior. My friends love to drive this car just for that fact...now if only I could get a 350's horsepower rating in it...My .02...:confused:
 

·
Registered
Joined
·
2,065 Posts
Speculation but I'll take a stab. CVTs don't like jerk (mathematical term - change in acceleration).

IMHO CVTs can handle good load, gobs of velocity and acceleration real well but jerk will eat them up. The band is not supposed to slip on the cones, what keeps them from slipping is good old friction, determined by surface area, materials and pressure. Static friction keeps it from slipping, once it slips then dynamic friction exists. Static friction is higher than dynamic. So the objective is to not exceed the static friction.

The torque converter is inherent in this process, provides slip until it locks up like at 18 mph, then is supposed to be direct drive to 40 then the CVT ratios kick in. The controllers also obviously play a part in this process.

Keep in mind I don't know, but this is how I visualize it.
 

·
Registered
Joined
·
6 Posts
i've noticed similar results switching from reverse to drive or vice versa while still moving in the first direction. for example, backing up then changing to drive without coming to a complete stop. since it's throttle-by-wire, the engine is not "forced" to respond to the pedal input. instead, it decides the amount of throttle to engage, and chooses less since it's going the wrong way.

one time i was going faster than normal and when i hit the gas in drive (still traveling backwards) the engine died. i think it's some sort of software protection mechanism.

just my .02.
 

·
Registered
Joined
·
487 Posts
I'm curious now... I'd like to know exactly what is working when and where in the MO when we drive it...

I haven't tried anything you guys suggested here... I keep the MO in drive at lights and my foot on the brake. Light turns, I swap to the gas and usually just gradually accelerate. If I punch it, I zoom. If I put it in Ds before giving gas, I zoom.

I always figured it goes like this... from 0 to 18, you're using a standard auto tranny, the same one that provides Park and Reverse. At 18, the CVT kicks in.

Now.. I don't know what the torque converter really does, but I know it isn't on when you're below 18 MPH. After 18 MPH, the torque converter kicks in? As does the CVT? But Enforcer said that the torque converter is working until 40 and then the CVT kicks in?

:confused: :confused:
 

·
Newbie
Joined
·
101 Posts
Discussion Starter #9
Enforcer said:
Speculation but I'll take a stab. CVTs don't like jerk (mathematical term - change in acceleration).

IMHO CVTs can handle good load, gobs of velocity and acceleration real well but jerk will eat them up. The band is not supposed to slip on the cones, what keeps them from slipping is good old friction, determined by surface area, materials and pressure. Static friction keeps it from slipping, once it slips then dynamic friction exists. Static friction is higher than dynamic. So the objective is to not exceed the static friction.

The torque converter is inherent in this process, provides slip until it locks up like at 18 mph, then is supposed to be direct drive to 40 then the CVT ratios kick in. The controllers also obviously play a part in this process.

Keep in mind I don't know, but this is how I visualize it.
The lag I felt is not your typical torque converter induced lag. In any automatic transmission, you still feel some acceleration even with the slight TC lag. In the situation I encountered, the car crept along at idle RPM even though you floored the gas pedal. It finally accelerated normally after 4-5 seconds. That is definitely abnormal behavior.

I theorize it may be something in one of the vehicle's stability control routines (AWD or VDC) that may take awhile to recognize the quick shift from N to D.

Or, in line with Enforcer's post, it could be something built-in to the software controlling the transmission that prevents anyone from 'drop shifting' (i.e. high revving the engine in neutral then dropping the shifter into drive) the transmission thereby over-stressing the CVT.
 

·
Registered
Joined
·
487 Posts
I believe stonemaster is right. We've all talked about the CVT "software" and how it intelligently handles the operation of the transmission. It would be foolish for Jatco/Nissan to NOT have failsafes in place to avoid damaging a very expensive transmission.

Still would love an in-depth look at the CVT and drivetrain function...
 

·
Registered
Joined
·
37 Posts
This is very interesting, but I'm not sure I really see it as a problem. I've driven manuals all my life until now and I _never_ felt the need take it out of gear when I'm stopped unless I needed to take my foot off the clutch for some reason. Similarly, I never feel the need to take the MO out of gear when I stop. This would bother me if it happened to me and I hadn't heard about it here, but for me at least, I don't think it will ever happen since I won't be putting it in neutral. I have put it in park at a light but put it back into gear before the light changed. No lag.
 

·
Registered
Joined
·
2,065 Posts
Doombringer said:

Now.. I don't know what the torque converter really does, but I know it isn't on when you're below 18 MPH. After 18 MPH, the torque converter kicks in? As does the CVT? But Enforcer said that the torque converter is working until 40 and then the CVT kicks in?

:confused: :confused:
OK let me try this again. The torque converter slips until it locks up (stops slipping) at 18 mph. Then from 18mph to 40mph the CVT is direct drive (meaning as speed increases so does rpm). Then from 40 on up you are on CVT ratio (meaning the CVT is changing the effective gear ratio). It's a little more complicated than that, depends on the sensors, controllers and throttle, but essentially this is how it works.

With that said, I know little about torque converters. What I do know is that they slip until a designed rpm is reached and then they lock up and stop slipping. The torque converter is like an automatic clutch in a manual transmission. It sits betwen the output shaft of the engine and the input shaft of the transmission. There are many reasons for this, allow the engine to increase rpms so you don't stall, get more power, prevent drivetrain damage, transmission damage, etc. The torque converter is in the CVT in the MOs case. But an automatic transmission has a torque converter between the engine and transmission (in the bell housing), and I have replaced these... and rebuilt a turbohydromatic 250 at the same time, but that is another story for another day. The torque converter in the MO has it's own controller according to the SM. Ergo therefore, the drop off you feel at 18mph is the torque converter unlocking and slipping as designed and computer controlled.

Make sense now?
 

·
Newbie
Joined
·
101 Posts
Discussion Starter #13
To add to Enforcer's torque converter explanation and to clarify 'slippage':

In a manual transmission, the output shaft on the engine is physically connected to the input shaft of the tranmission by the clutch pad and clutch plate. To shift gears, the pad is pushed away from the plate by the clutch pedal, you shift gears, then release the clutch which engages the plate. It's the opposite of a brake pad and rotor (or drum) where you press the pedal to engage the braking system.

A torque converter (TC) is essentially a 'viscous' connection to the automatic transmission, instead of the physical connection in a manual set-up (disregarding lock-up TC's for now). The torque created by the engine drives the fluid inside the TC which, in turn, transmits the power/torque to the automatic transmission (AT).

Go to these sites to get a good explanation on how it works, complete with photos:

http://auto.howstuffworks.com/torque-converter1.htm
http://auto.howstuffworks.com/framed.htm?parent=torque-converter.htm&url=http://www.familycar.com/transmission.htm

In low torque conditions (like at idle), the TC 'slips' (internally) to allow the engine to run without engaging the AT. Otherwise the engine would die each time the car came to halt. As you accelerate, the increase in torque induces the TC which starts to slip less and less, transmitting engine power to the AT. At a certain point, a normal TC is almost like a manual clutch in that power going in is nearly identical to power going out. However, because the connection is a fluid connection, there will always be some slippage. This is why AT's get worse gas mileage than MT's.

Enter the lock-up torque converter which was created to eliminate this slippage at higher speeds. It creates a physical, direct connection between the engine and AT eliminating slippage while improving mileage and power.

A lock-up clutch inside the TC is designed so that when it engages (at 18 mph in the case of the MO), the TC is already slipping very little so the action should be barely perceptable. Same is the case when it disengages.

The TC is a seperate mechanism from the CVT (which is a special kind of AT) though they work together. The TC's purpose is to transmit power to the CVT. The CVT's purpose is allow the vehicle to operate at high speeds using the narrow power range of the engine by switching effective 'gear' ratios ( though it's a bit more complicated than a standard AT).

The CVT begins shifting ratios the moment you step on the gas independent of the TC. If it didn't, the engine would rev so high that by just 5 MPH or so, it would shut-down (or blow-up if it weren't electronically restricted). If you ever tried driving in 1st gear with a manual transmission (or L1 in a normal AT), you know you cannot go very fast though the engine is screaming. The transmission MUST shift ratios to keep the engine in an optimal power range.

Since the CVT's shift of gear ratios is pretty seamless, you cannot 'feel' the transmission changing gears as you accelarate which makes the lock-up of the TC more perceptable.
 

·
Registered
Joined
·
360 Posts
So, you want the CVT to act like a straight? Then get a straight!
You want the CVT to work like a "geared" automatic? Then get a "geared" automatic!

I would like my pickup to handle snow like a 4X4. But I didn't BUY a 4X4, so I don't whine about it.
I would like my 450mHz craptop to perform like a 3gHz desktop. But I bought the craptop, so I don't whine about it.

So much for the rant.

Now for a few facts and a bit of plain old common sense:
If you read up on the CVT, you'll find lots of warnings about preserving belt life. After all, the belt is the heart and soul of the CVT. Many of the warnings are against things that will shorten the belt life.
Stop a backward roll by shifting from R to D?
Rev 'er up while holding the brakes in order to bark the tires?
Rev 'er up in N and drop into D to bark the tires?
Drop from D to S (or L) while cruising along at about 85mph?

Congratulations! You just significantly shortened the lifespan of the belt in your CVT!!

Now for the bit of common sense:
Ya think the CVT does NOT have some safeguards built in to reduce some of the wear and tear on the belt? Think again....


We now return to the rant:
Want a sports car you can burn doughnuts in, play like you're in 2 Fast, 2 Furious, go 0 to 60 in LESS than 7, or go from 55 to 75 in less than 2?

What were you thinking when you bought a Murano instead of a Z?
 

·
Registered
Joined
·
3 Posts
Hesitation...sort of

Once when I was driving up a steep SF hill I had to slow down due to traffic in front of me. When the cars ahead of me cleared up and I attempted to accelerate my MO just inched forward no matter how much gas I gave her. I stopped completely, put it in P and then back to D and it was okay, but I was a little concerned. Anyone else have this same problem or can anyone explain the phenomenon
 
1 - 16 of 16 Posts
Top