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Discussion Starter · #1 · (Edited)
Shortly after we bought our 2007 Touring I was closely watching the instant fuel economy while on a long road trip on the prairies. No mountains --and extremely long stretches of perfectly flat highways. There was no noticeable wind or wind changes that day.

Usually the ECO mode worked fine and I could feel the VCM kick in (no complaints about that) but then occasionally it would either kick out, or change modes or something, and the display would show the fuel consumption jump up to twice as much --and stay there (still showing that ECO mode was engaged) unless road or wind conditions changed significantly enough for the ECO light to go out.

When I would notice the problem I could solve it by just quickly tapping the gas pedal just enough to force the VCM to shut off and make the ECO light go out, and then instantly it would go back into ECO mode and work properly using much less fuel --as should be expected.

Some days this happens infrequently or not at all for hours, but other days at times I literally have to tap the gas to fix it two or three times PER MINUTE. The ECO light will turn on (as it should) when the VCM kicks in, and it's showing great fuel economy --then within seconds the fuel economy drops to half while the ECO is still showing as active.

Just so you know I'm not crazy, when it happens I can literally step on the gas lightly (which turns off the ECO light and VCM) and begin ACCELERATING using LESS fuel than it was showing while ECO & VCM were engaged, and the instant fuel economy show it is clearly much better.

I took it in several times and tried to explain the issue but of course it didn't happen on the road test by technicians (or they weren't really paying attention) and they kept saying it was fine, and that I just didn't understand how it worked because fuel economy changes with driving conditions basically calling me an idiot or a liar after several years of complaints.

I gave up trying to get them to acknowledge there might be a problem, then I decided to do a whole trip without tapping the gas to fix it. I tracked --exactly-- how much gas I used for 40 hours of driving and sure enough, the poor fuel economy shown on the trip computer from letting the ECO use double fuel when it was on matched exactly the actual fuel consumption.

This proved two things; 1--The trip computer wasn't faulty. 2--The ECO/VCM weren't functioning properly because they were actually using the double amount of fuel being reported by the engine computer.

Has anybody else heard of this, and does anyone know what could be done to fix it?

I can only imagine what is really happening is that the cruise control is trying to maintain speed and the VCM disengages and fuel is then being injected into all 6 cylinders, but only 3 spark plugs are firing so half the fuel is being wasted providing no acceleration to maintain speed on cruise control.

Am I the only one in the world who has experienced this?
 

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Easy fix. Muzzle the VCM.
Agreed. @bterrynew, you should disable VCM - Here's the link to the sticky thread which explains why:


I disabled mine and find that my highway fuel economy tracked by dividing the miles between fillups with the gallons I put in the tank, is no worse, and sometimes as much as 3 MPG better than when VCM was enabled. It's speculation, but I travel around 80 MPH so the ECO light would only stay on for short periods of less that 30 seconds at a time and that switching between 3 and 6 cylinders is counterproductive compared to having all 6 cylinders firing all the time. I definitely like that it is much smoother and more responsive with all 6 cylinders active at all times.
 

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VCM is not as efficient as you think it is.
 
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I would not believe any Fuel mileage info displayed. I don’t think it is very accurate, reliable or useful. Ignore it.

Muzzle your VCM to prevent major engine damage.
VCM does not improve fuel efficiency very much. Perhaps 1-2 MPG. Sometimes it makes it worse.
 
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I would not believe any Fuel mileage info displayed. I don’t think it is very accurate, reliable or useful. Ignore it.
I wonder if anyone has ever verified the accuracy of the 'instant mileage' reading. Is it even possible for anyone without a laboratory and a dynamometer?

I use it in the same way I used to use the vacuum gauge. When vacuum was low, the engine was working hard. I might consider easing up on the throttle. When the momentary mileage indication drops, the engine is working hard. That's about all you can conclude.
 

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One important thing to keep in mind is that the ECO light can be on regardless of whether the engine is in 3 or 6 cylinder mode. When you see lower instant fuel economy on the gauge with ECO light on, you are most likely running in 6 cylinder mode. In this situation, a slight lift of the gas pedal should be enough for the engine to transition into 3 cylinder mode.

Also, it is known that all spark plugs fire regardless of whether the engine is in 3 or 6 cylinder mode. This is so that the temperature of deactivated cylinders can be somewhat maintained while cruising.
 

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Also, it is known that all spark plugs fire regardless of whether the engine is in 3 or 6 cylinder mode. This is so that the temperature of deactivated cylinders can be somewhat maintained while cruising.
[citation needed]

If this was the case, the plugs wouldn't be getting oil fouled. And if this were the case and any oil got in the cylinder, the spark plug would be burning it with nowhere for it to go since the valves are kept closed.
 

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Also, I believe the 2007 has VCM2 where it also has a 4 cylinder mode.

I see it's been 2 days since the first post so who knows if the OP will return. If you do, take the advice above and disable VCM altogether before you have bigger issues than "what is my instantaneous fuel readout doing?"
 

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Also, I believe the 2007 has VCM2 where it also has a 4 cylinder mode.
It does not, VCM-2 was brought to the Odyssey in 2008 with the mid-cycle refresh. 2007 just got the new ECT-1 connector but still uses VCM-1.
 
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When the ECM initially turns on, the fuel economy is significantly better. I'd prefer to fix the cause and keep it on if I can.
Please, do yourself a favor...Just disable the VCM. There is no "fix" for it. If you don't disable it you risk fouled plugs, stuck piston rings, worn out expensive engine mounts, and burned up catalytic converters. The only "fix" for VCM is to disable it. This is not exclusive to Honda. GM has a similar system called DoD or Displacement on Demand or Active Fuel Management. It has destroyed GM engines, as well. Whatever fuel savings you think you're getting will be lost exponentially if/when you start to have these problems.
 

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Discussion Starter · #14 ·
I would not believe any Fuel mileage info displayed. I don’t think it is very accurate, reliable or useful. Ignore it.

Muzzle your VCM to prevent major engine damage.
VCM does not improve fuel efficiency very much. Perhaps 1-2 MPG. Sometimes it makes it worse.
I've tracked precisely the fuel economy by actual miles and gallons for long trips (with and without manually correcting the issue), and it matches the display.

The display is correct when showing improved fuel
Also, I believe the 2007 has VCM2 where it also has a 4 cylinder mode.

I see it's been 2 days since the first post so who knows if the OP will return. If you do, take the advice above and disable VCM altogether before you have bigger issues than "what is my instantaneous fuel readout doing?"
 

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Discussion Starter · #15 ·
I've tracked precisely the fuel economy by actual miles and gallons for long trips (with and without manually correcting the issue), and it matches the display.

The display is correct when showing improved fuel
If I do turn it off it will certainly be interesting to see if (when VCM would normally kick in) fuel economy improves or stays the same with all 6 cylinders firing.

Considering that it would normally be on when there's less load on the engine perhaps having all 6 will use far less fuel anyway.

Maybe less efficient if VCM was working properly, but it's clear that it could be causing other more costly problems in the long run that aren't worth a few mpg.

We have never noticed any vibration issues or other reported problems, but maybe we've just been lucky so far.
 

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Discussion Starter · #17 ·
I've tracked precisely the fuel economy by actual miles and gallons for long trips (with and without manually correcting the issue), and it matches the display.

The display is correct when showing improved fuel
If I do turn it off it will certainly be interesting to see if (when VCM would normally kick in) fuel economy improves or stays the same with all 6 cylinders firing.

Considering that it would normally be on when there's less load on the engine perhaps having all 6 will use far less fuel anyway.

Maybe less efficient if VCM was working properly, but it's clear that it could be causing other more costly problems in the long run that aren't worth a few mpg.

We have never noticed any vibration issues or other reported problems, but maybe we've just been lucky so far.
 

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When the ECM initially turns on, the fuel economy is significantly better. I'd prefer to fix the cause and keep it on if I can.
This is not accurate. Fuel economy is never significantly better with VCM. You are being duped by believing what the display is showing you. Please muzzle your VCM. It will cause you major issues.
 

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Maybe less efficient if VCM was working properly, but it's clear that it could be causing other more costly problems in the long run that aren't worth a few mpg.

We have never noticed any vibration issues or other reported problems, but maybe we've just been lucky so far.
Noww you're on the right track. There are no noticeable symptoms. For most, the VCM system does its thing with no noticeable problems.

However, at some point it will happen... You'll get misfires and find oil fouled plugs. You'll take it to the dealer where they will tell you that it needs new piston rings for $5-6k. You'll jump online and find this issue is widespread and was the subject of a class action law suit. You'll find you could have prevented it by simply disabling VCM with a device that costs $129 and 10 minutes to install.

How do we know this? Because people post here every day with this exact complaint.

It's your car and you can do as you please. My suggestion is disable it.
 
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