mondster

Had the tsb 38 update last week and i noticed a drop in mpg. Also noticed that i no longer get the sudden drop in rpm while cruising on the highway, both on normal and sport mode. Car seems smoother now as well since i guess the "minor" vibration caused by the vcm is gone. Anyone else notice these differences after having tsb 38 applied? Car also seems to pick up quicker when gas is pushed.

sbillard

Have not heard of VCM disable, but other things have not worked when the update was done incorrectly. For me it was the Auto Idle Stop. I got the update re-done and all was well. Others have said that AIS magically came back after a while.

mondster

I guess i dont mind vcm being disabled. Good thing gas is cheap now. I did see a couple of people here post that their mpg went down after getting tsb 38 and 40

mondster

Btw, my rpm while cruising before the update @75mph would be around 1400. Now it sits at around 1800.

Jayellin

I had the 034 update which includes the 038 Also noted the quicker response to the accelerator and lost the auto idle stop About one month later the auto stop came back and the acceleration also seems back to the way it was before the update. In my car it's not bad and I have no hard shifts but as others have noticed the updates dot seem to last and the car somehow relearns old behavior

flybyglass

I have noticed much smoother shifting in Normal mode. Sport is slightly abrupt in certain gears (I think 2nd - 3rd) but nothing objectionable as I believe that is when the dog clutch engages. Try different IDS modes and see how it is.

mondster

My normal is still harsher than the sport. But with sport i have to make sure it shifts at a higher rpm, otherwise i get a slightly hard shift.

Still trying to figure out if the drop in mpg is caused by vcm being disabled.

mapleloaf

Had the 38 done twice (Canadian equivalent). Gas mileage did drop but i THINK it's levelling off. Less hesitation upon rapid acceleration, and improvements in shifting, particularly 1-2 shift. The 2-3 shift was generally okay under 2k rpms or over 3k rpms before the update and now. It did seem after the update that the 2-3 shift started taking place closer to 3k rpms more frequently with similar acceleration, perhaps explaining gas mileage drop. In the last few days it seems the 2nd shift is smoother at any rpm, ironically after i drove guys around for the Grey Cup celebration. That might reinforce other posters suggesting that added weight helped.

Did not notice change in VCM. I had noticed VCM more at lower cruising speeds (30 - 45 mph) than I did at higher speeds, where it hasn't been an issue, likely because 3 cylinders are shutting down rather than two. This happened before the update, with no discernible change after the update.

Rocketsfan

mondster,

When you say your mileage dropped, how much are you saying it dropped (I may have missed it)? The reason I ask is that I've taken very similar long road trips to the same destination, following the same path, using the same gas station to fill up, and the trip was 95-98% highway/freeway miles where the mileage varied by 3-3.5 mpg. And that was before either update.

BTW, I had TSB 38 installed back in early August, I believe and TSB 40 was done on November 20th. I'm going to be doing a quick road trip pretty soon, so I'll let you know what kind of mileage I'm getting.

Rocketsfan

As promised above, I took a quick road trip where I measured my gas mileage on pretty much pure interstate driving. I took a trip from Dallas to Arkansas and back. The path I took up there and back were mirrored (well, except for about .3 miles). I put IDS on ECON for both ends of the highway trip. I replaced the cabin filter and the car's engine/air filter before the trip. The temps were anywhere from the low 40's to upper 40's during both trips. I tried to use cruise control wherever possible and stuck to about 5 mph above the speed limit except in areas I know that're probably speed traps. lol. The readings were both off the MID :

Trip to Arkansas :
Gas : Exxon 93 octane
Total miles : 266.2 miles
Avg. speed : 64 mph
MPG : 35.1

Trip back to Dallas :
Valero 91 Octane
Total miles : 266.5 miles
Avg. speed : 64 mph
MPG : 36.8

Also, while driving, I noticed that while cruising at 70-75 mph'ish, my RPM's were always around 1500-1700.

In all honesty, I was expecting a bit more in the MPG's, but when I thought about it, while I've made this trip several times, I don't believe I've done it in this car, so maybe the mileage is ok for this trip. I know on trips to Houston and back, I've gotten anywhere from 35-39+ mpg's, so there's always a variance on the same trip. I'll be taking a trip to Houston in the future, so hopefully I'll remember to watch the mileage.

My initial assumption is that even if the updates did affect mileage, it doesn't seem to be by much. A drop in mileage on the same trip of 1-2 mpg is almost meaningless since any number of things like temperature, average speed, etc. could affect the mileage of the car.

Note : I'm driving a FWD V6, not the SH-AWD.

mondster

I guess i just overreacted. Seems like my mpg is now similar to pre tsb 38. Lol

Mike_TX

Wait a minute. I thought VCM always shut down 3 cylinders. Are you saying that's changed?

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mapleloaf

I think it's been that way for several years, as per the Acura video from 2014. The engine operates at 3, 4, or all 6 cylinders depending upon power requirements.

Rocketsfan

To my knowledge VCM only shuts down to 3 cylinders on the TLX. Earlier Honda engines used 3, 4, or 6 with VCM, but once they switched to the newer direct-injection engines, they also went to either operating at 3 or 6 cylinders with the VCM. From what I recall this was due to the fact they could produce enough torque with only 3 cylinders so that they didn't ever need to switch to 4. I believe the first year the RDX was out, it used the 3/4/6 version of VCM (?)... not sure about subsequent years.

sbillard

Car in the video sure looks like the TLX!

Rocketsfan

Looks like a cartoon to me!

The video may have been made before Honda switched from 6-4-3 to 6-3. Here's a Honda press release soon after the unveiling of the TLX :

Honda Worldwide | April 16, 2014 "Production-Ready 2015 Acura TLX Unveiled at the 2014 New York International Auto Show"

From the link :

The direct-injected 3.5-liter SOHC i-VTEC V-6 incorporates Variable Cylinder Management (VCM), with the ability to deactivate three of the engine's six cylinders, for improved fuel efficiency.

Another Honda.com link from 2014 :

2015 Acura TLX: Powertrain - Honda.com

To boost fuel efficiency, Variable Cylinder Management (VCM) automatically deactivates three of the engine's six cylinders under light engine loads.

mapleloaf

Thanks for the update. Perhaps it's simply more noticeable at lower cruising speeds.