Unusual Deceleration

[UOENO]

Hi everyone,

I've gotten a lot of good information by reading various posts and figured I'd give it a try at this point, but bare with me because I am not very knowledgeable when it comes to cars. I just recently purchased an 07 M35x and the problem I feel I'm having is when I take my foot off the gas it decelerates a lot quicker than I feel it should (doesn't coast much at all... if at all). I understand it's AWD and is completely different than my girlfriends Pontiac Vibe, just for example... but even when I'm going down a hill it seems like something is holding me back from coasting because my speed does not increase at all...it still gradually slows down which is quite odd to me especially since I'm going down a damn hill. I'm not sure if I'm nit picking at this point or not, but I also feel a little jerk (nothing too crazy) when it downshifts while slowing down and am not sure if its related or if that is normal. It all seems involved with the unusual deceleration when I'm driving, but I could be very wrong on that.

I'm just concerned I have some internal issue that will cost me down the road and I'd preferably like to figure it out before that day comes knowing Infiniti isn't the most friendly when it comes to repair costs.

Also, to top it all off, I've read just about every M forum out there to see about improving gas mileage because I'm average about 16.5 (highway/city combined) overall based off my fuel economy information. I know the M35x isn't known for its awesome gas mileage lol, but I feel that is a bit low based off of posts I've seen and the amount of highway driving I do. Basically I feel like whatever it is that is slowing me down is affecting my gas mileage as well.

Don't laugh too hard if I sound nuts, but if there are any suggestions or if someone has experienced this I'd love to hear what was done to fix or improve it. If this is normal for the M35x, please also let me know. Would be nice to hear an opinion from someone much more knowledgeable. Thanks in advance for your time.

[ArmedAviator]

It should coast like any other automatic car on the road. You do not sound crazy.

First things to check:
1. Can you put the car in neutral and roll it by hand on flat level ground? Be sure someone is in the driver's seat to apply the brakes just in case.

2. When driving and you decelerate, shift into neutral. Does the excess drag seem to disappear or is it still present?

If #1 doesn't work, I'd suspect a stuck caliper. If #2 doesn't work, it's a drivetrain issue.

[UOENO]

It should coast like any other automatic car on the road. You do not sound crazy.

First things to check:
1. Can you put the car in neutral and roll it by hand on flat level ground? Be sure someone is in the driver's seat to apply the brakes just in case.

2. When driving and you decelerate, shift into neutral. Does the excess drag seem to disappear or is it still present?

If #1 doesn't work, I'd suspect a stuck caliper. If #2 doesn't work, it's a drivetrain issue.

I haven't tried rolling it on level ground while having it in neutral, no. I will definitely try that when I have a second... But I have put it in neutral while going down the hill for example and the tension/excess drag does disappear/go away.

[Ilya]

Welcome to the forum!

Are you by any chance in manual mode when you're experiencing this 'drag'? This is known as engine breaking and is normal in that mode. If your caliper is seized or sticking, you might be able to look at the rotor and see 'grooves' (it should be generally smooth). Or more brake dust on one wheel compared to the others.

As for fuel economy, really hard to tell you anything without knowing the maintenance history of your car, mileage, etc. Could be anything from spark plugs being old to old O2 sensors to improper inflation of tires to stuck caliper to...well you get the point.

[UOENO]

Welcome to the forum!

Are you by any chance in manual mode when you're experiencing this 'drag'? This is known as engine breaking and is normal in that mode. If your caliper is seized or sticking, you might be able to look at the rotor and see 'grooves' (it should be generally smooth). Or more brake dust on one wheel compared to the others.

As for fuel economy, really hard to tell you anything without knowing the maintenance history of your car, mileage, etc. Could be anything from spark plugs being old to old O2 sensors to improper inflation of tires to stuck caliper to...well you get the point.

I haven't messed around with the manual mode too much, but I'm positive it is not in manual mode when I'm experiencing it. Also, I will have to take a look when I get home to see if I can see any grooves, dust, etc. I'm hoping it is something simple like a caliper as you guys have mentioned. As far as my fuel economy goes, I'm not overly concerned with that as I'm sure I need to get it in for somewhat of a tune up soon. I just figured I'd mention it because... well, trying to think logically about this.. if something is dragging/slowing me down I would assume it would affect my mpg so if I can figure this out maybe I'd solve both my problems.

Going back to what ArmedAviator said.. does it mean anything that when I put it in neutral the 'drag' goes away and I can feel a normal coast???... if that makes sense?

[ArmedAviator]

Can you safely takes video of the deceleration occurring when in gear and another in neutral? I'm curious what the tach is doing. You might have a transmission issue....or the previous owner may have tuned it shift schedule that aggressively downshifts whenever you let off the gas with the expectation of "hey you must be slowing down for a corner on racetrack, let me get you ready to accelerate out of the turn." A previous tune I used had that option. It was fun, but got annoying quickly daily driving.

[steve_c]

I am not convinced you have a problem.
Our cars do have considerable drive-line drag as compared with conventional 2x drive vehicles.
front transfer case, front differential & drive-shaft are the key components.
The deceleration characteristics of your car sound similar to those of my M35x.

I am not saying your situation could not be exasperated by a mechanical problem, but based on the info
you have posted, I cannot see it as of now.

If a caliper were dragging, the wheel of the problem caliper would get hotter than the other three. Additionally,
you would likely feel a slight to moderate wheel pull especially as the brakes heat up.

My wife averages (combined city/highway) anywhere from 16.5 to 17.2 I do high 17's to mid 18's under same conditions as she does in the same car. Our driving habits are very different. Straight highway, no city I can manage high 21/low 22 mpg's on fairly flat terrain.

These cars have a really nice instant mpg readout on the NAV screen. You can reset your MPG averages at any time you want while you practice
MPG strategies.

One caution, from my experience, DO NOT look at or reset the instant/live MPG screen while driving, it is a distraction that could lead to an accident.
I learned my lesson with that, coming close to rear ending a car once!

[UOENO]

Thanks everyone for all your input, its appreciated. Last comment from steve_c puts me at ease a little bit just due to the fact that you experienced similar things with your m35x with no issues, but I did go ahead and check my calipers and there is no sign of extra dragging/grooves/etc.. while in neutral I could easily push it on my own on flat ground.... so I think that we can rule out the possible caliper issue. Few details that might help here for further discussion that I think I missed - Just to clear up a few things too...

I don't feel any issues when accelerating as far as it being "jerky" when upshifting. But going back to coasting/letting off gas - it seems to be intermittent where it jerks a bit when slowing down and once it jerks I can see my RPM bounce, which I'm thinking is a downshift, and that is when I can feel a little bit of the drag go away for a second but at that point I've already slowed down quite a bit. What I just described is more city driving, but is noticeable on the highway as well. One thing I did just notice is that I am leaking transmission fluid....which is bad, obviously. Not a bad leak, but I'm going to have it checked out and the person/dealer who sold me the car is happily working with me, but I guess my question at this point is can a transmission fluid leak cause the issue I feel I'm having with coasting/decelerating? Apologize for repeating myself, but I feel I left out a few details that I should have included and I just noticed the leak last night on my garage floor.

Regardless.. steve may be right and I might be overreacting to something that is just normal with the m35x. My gas mileage isn't horrible based off of what I've seen others post and I knew it wasn't the most efficient when I bought it.

Big thing at this point is that I'm leaking transmission fluid and need to get that fixed asap. Let me know your thoughts, thanks.

[ArmedAviator]

sreve_c, I disagree based on the OP's latest response that putting the transmission in neutral relieves the symptom he is describing. When in neutral, all the other drivel and drag is present downstream (so to speak) of the transmission output shaft.

This is clearly transmission related.

OP, any luck taking video of the issue?

[UOENO]

I have not been able to take a good video yet, but I will definitely do that on my way home tonight from work. Even though steve_c says his is similar... I know nothing when it comes to cars, but something does feel off.

I need to get the leak fixed, no doubt, and it would be nice if that resolved my problem... but I'm still not 100% sure that would cause what I'm experiencing.

[Ilya]

sreve_c, I disagree based on the OP's latest response that putting the transmission in neutral relieves the symptom he is describing. When in neutral, all the other drivel and drag is present downstream (so to speak) of the transmission output shaft.

This is clearly transmission related.

OP, any luck taking video of the issue?

To be fair, there is a certain amount of 'engine braking' when in gear. When you go into neutral on ANY car, you will get a relief of that same symptom. Same on my motorcycles. Motorcycles engine brake probably 50% harder than cars...to the point where I sometimes wouldn't even use my brakes. I would just blip the throttle, drop a gear and let the clutch out and let the bike do it's thing...particular in the city, etc.

Still would be curious to see video(s).

[ArmedAviator]

sreve_c, I disagree based on the OP's latest response that putting the transmission in neutral relieves the symptom he is describing. When in neutral, all the other drivel and drag is present downstream (so to speak) of the transmission output shaft.

This is clearly transmission related.

OP, any luck taking video of the issue?

To be fair, there is a certain amount of 'engine braking' when in gear. When you go into neutral on ANY car, you will get a relief of that same symptom. Same on my motorcycles. Motorcycles engine brake probably 50% harder than cars...to the point where I sometimes wouldn't even use my brakes. I would just blip the throttle, drop a gear and let the clutch out and let the bike do it's thing...particular in the city, etc.

Still would be curious to see video(s).

Absolutely true, but the OP seems to have compared this abnormal drag to the engine braking to other automatics. I have driven a G35 before, and while the M35 is a bit heavier and a different final drive ratio, the engine braking/driveline drag shouldn't be increased by an immediately noticeable amount.

OP, until you get some videos, can you tell us if the RPM stays the same, increases, or decreases when letting off the gas to coast?

[steve_c]

To be fair, there is a certain amount of 'engine braking' when in gear. When you go into neutral on ANY car, you will get a relief of that same symptom. Same on my motorcycles. Motorcycles engine brake probably 50% harder than cars...to the point where I sometimes wouldn't even use my brakes. I would just blip the throttle, drop a gear and let the clutch out and let the bike do it's thing...particular in the city, etc....

Absolutely!
I use deceleration in lieu of braking to slow down whenever I anticipate coming to a light or slow down situation.
Don't forget these cars feature rev-matching, in which the engine & transmission speeds are matched to avoid excessive engine up-revs due to mismatched transmission gearing to engine RPM's. While out in the M yesterday, I decelerated and saw the same tach blip Ueno describes as the car slowed down a bit.

Ueno, Transmission fluid level is critical. There is a dipstick on the passenger side of the firewall right behind the engine. It is capped, and has a 10mm bolt securing it to the "charge tube" as it is called. Best results are to check it when the engine & transmission are warm, (15 minutes or so of moderate driving on a cold engine).
hopefully, the leak is coming from the transmission pan drain plug or something similarly simple.

[TDot]

I'm being lazy and havent read the entire thread...or even the entire OP, but there is nothing wrong with what you've described that I've read. This car will start slowing down by itself in automatic and manual when it's in second gear, and considerably more in first gear. Sorry if I missed anything else beyond that.

[Brian35XR]

I disagree with the point that this car should coast like "any other automatic car on the road". This car has much more aggressive engine braking than any other car I've owned. I pretty much notice no coasting from this car what-so-ever. Even on a road with a slight decline if I want to keep a steady MPH, I have to apply at least some degree of throttle else the car will automatically try to downshift through all of the gears as soon as I let go of the gas peddle.

I've even had a G35 (rwd) before this and that thing would coast forever without having to apply much throttle to keep up a 'cruising' rate of travel. Whether it's due to the additional drive-train components like such as the transfer case, front differential, etc.. or some aggressive transmission programming, this car's acceleration behavior feels like trying to cruise in a "tank".

[UOENO]

Sorry for going M.I.A. everyone, just moved into a new house and been busy. Anyway...

Long story short - The day after I noticed the transmission fluid leak is the day it started driving much better. Ironic, right...

The jerk when decelerating/downshifting went away and I could feel that the tension/drag went away as well. At this point I'm thinking there was too much transmission fluid (not 100% sure though). Just basing that off of general transmission/transmission fluid posts online.

Buddy of mine recommended I take it to one of his trusted mechanics with a hoist.. lifted it and found that my transmission oil cooler hose was deteriorating and leaking along with old clamps and the same with my coolant hose which was great considering that it cost me $5 for parts vs. however much for a possible bigger issue.

We ran to auto part store, bought some high pressure hoses and higher quality clamps and wah-lah - leak fixed and is driving fine to this day.

Just figured I'd update the post with my resolution. Thanks for everyone's input, much appreciated!