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Discussion Starter · #1 ·
My gas mileage has been dead on, and I mean dead on at 21 mpg suburban driving for the 6 years that I have owned my 2008 Accord V6 Sedan, at most fluctuating by 1 mpg. However, about 2 months ago my mpg's instantly dropped to a predictable and miserable 16 mpg at every fill-up. I check my fuel economy every month or so, so I know this was not a gradual change, but happened immediately after one of my regular checks. This is not a weather related issue, a driving style issue, I have made no changes to the vehicle, nor have any other factors changed. There are also no warning lights on the dash. I am not sure what would cause such a drastic drop. I dirty MAF sensor would have happened gradually, unless it is malfunctioning. Not sure where else to look. Hopefully it isn't the start of the whole engine lawsuit thing, although there is no obvious loss of oil judging merely by the dipstick level, which I also check regularly. Any ideas?

I do have a OBD II plug in module which allows me to look at the readings on my smartphone, but since I don't have a baseline, I don't know what would be normal for things like the fuel/air mixture, etc. It would be great if someone could provide that baseline from a normally working 2008 Accord V6 Sedan.
 

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Elvira
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My gas mileage has been dead on, and I mean dead on at 21 mpg suburban driving for the 6 years that I have owned my 2008 Accord V6 Sedan, at most fluctuating by 1 mpg. However, about 2 months ago my mpg's instantly dropped to a predictable and miserable 16 mpg at every fill-up. I check my fuel economy every month or so, so I know this was not a gradual change, but happened immediately after one of my regular checks. This is not a weather related issue, a driving style issue, I have made no changes to the vehicle, nor have any other factors changed. There are also no warning lights on the dash. I am not sure what would cause such a drastic drop. I dirty MAF sensor would have happened gradually, unless it is malfunctioning. Not sure where else to look. Hopefully it isn't the start of the whole engine lawsuit thing, although there is no obvious loss of oil judging merely by the dipstick level, which I also check regularly. Any ideas?

I do have a OBD II plug in module which allows me to look at the readings on my smartphone, but since I don't have a baseline, I don't know what would be normal for things like the fuel/air mixture, etc. It would be great if someone could provide that baseline from a normally working 2008 Accord V6 Sedan.
the amount of the drop is about equal to 1/6. this could mean a bad spark plug cable or bad spark plug. Do you have cables or does it have coil on spark?

Check that first for loose cable bad spark plug before worrying too much.

Let us know what you find.

Miker
 

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Elvira
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Well?
What did you find out?
Miker
 

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Discussion Starter · #4 ·
Well?
What did you find out?
Miker
It has been in the single digits/teens here, so it is going to be a while before I can look at it. Besides, my tools are packed away in storage, so if it isn't something simple and obvious, I probably will be forced to have a mechanic look at it or just live with it.
 

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Elvira
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It has been in the single digits/teens here, so it is going to be a while before I can look at it. Besides, my tools are packed away in storage, so if it isn't something simple and obvious, I probably will be forced to have a mechanic look at it or just live with it.
I hear you. Didn't want to come off badly just a lot of posts go unanswered. I posted my answer because I always found, on a 4 cyl, an immediate drop of close to 25% in mpg I always found it to be a bad cable. Hopefully it will be that simple for you.
Keep warm and keep us posted. :thmsup:
Miker
 

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Reset your ECU by unplugging the battery, your car memory will be wiped out so once its reset the car needs to relearn your driving habits or you could buy a bottle of techron and pour it down your gas tank which helped restore my MPG.....
 

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Discussion Starter · #9 ·
Miker, you had asked me if I ever got around to changing the plugs. I just got to it about 4 weeks ago and went through a couple of fuel fillups with no improvement in fuel mileage. All the plugs were very clean except for Plugs #2 (worst) and #3. I suspect the corrosion on these two plugs is VCM related, but I don't imagine there is enough buildup to have caused any problems. So far I have also cleaned the MAF sensor, changed the air filter, checked obvious things like tire air pressure, etc., without any improvement. As a last act of desperation I changed fuel suppliers with no change. I am out of ideas at this point. I didn't mention it before, but I have 37,636 miles on the Accord.

Here are the plugs starting with #1 on the left, then 2,3,4,5,6.

Spark plug Auto part Automotive ignition part Automotive engine part Suspension part
 

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"Old School" Shifter
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A brake dragging? After you drive it check the heat of the brakes by putting your hand close to the middle of the wheels. Anyone feel hotter than the others? Maybe smell different?

Maybe your injectors are dirty.
 

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using your OBD2 monitoring device, check your short term and long term fuel trim values..just curious as to what they are.
 

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Discussion Starter · #12 ·
using your OBD2 monitoring device, check your short term and long term fuel trim values..just curious as to what they are.
I will give that a look tomorrow morning, as I will be working on the car anyway...and it will be a more pleasant temperature outside. The rubber door molding has been falling down for the last 2 years on one door, and now it is happening on two doors, so I guess its time to tack all four of them up with 3m Weather Strip Adhesive.

I am not sure what the trim values are exactly called on the Accord and/or on the OBD2 reader, but I will look for anything with the word "trim" or “fuel” in it.
 

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I will give that a look tomorrow morning, as I will be working on the car anyway...and it will be a more pleasant temperature outside. The rubber door molding has been falling down for the last 2 years on one door, and now it is happening on two doors, so I guess its time to tack all four of them up with 3m Weather Strip Adhesive.

I am not sure what the trim values are exactly called on the Accord and/or on the OBD2 reader, but I will look for anything with the word "trim" or “fuel” in it.
you might see 'stft or ltft' on the screen. Really if everything was perfect the trims should be near zero. If the values are high, or the LTFT is high, then the ECU is adding fuel for some odd reason, when it shouldn't be.
 

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The fuel trims are base at 0 the short term fuel trim is dynamic every time you start the car, long term fuel trim is stored in the ECU. The numbers indicate in a percentage how much fuel is added or subtracted from the base program. The check engine light does not come on until fuel trim hits 30% off base. It will give you an indication what is going on. The fuel trim is done by banks, in the V6 you have 2 banks, bank 1 is the rear cylinders 1,2,3 and bank 2 is the front cylinders 4,5,6. The short term and long term fuel trims are calculated by bank from information provided by the upstream O2 sensor.

Sent from AutoGuide.com Free App
 

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I agree - brake drag is a big thing overlooked.

like you said - checkrf for debris in the maf sensor?

try a different gas station?

checked tire pressure?

cold weather will kill fuel economy as well (winter blend fuel)
 

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Discussion Starter · #16 ·
using your OBD2 monitoring device, check your short term and long term fuel trim values..just curious as to what they are.

NOTE: All the values below are at idle after the engine has reached operating temperature (As in temp gauge needle on dashboard stabilizing).

These are the only trim readings my BAFX ELM327 OBD2 device can read, unless someone can tell me where I can find a predefined Honda Accord PID list for the Torque app. The trim readings are:
Fuel Trim Bank 1 Sensor 2 = 0.8 %
Fuel Trim Bank 2 Sensor 2 = -1.6 %

Other engine type readings:
O2 Volts Bank 1 Sensor 2 = 0.6 V
O2 Volts Bank 2 Sensor 2 = 0.6 V
Mass Air Flow = 3.4 g/s
Intake Manifold Pressure = 28.0 kPa
Barometric Pressure = 101.0 kPa
Timing Advance = 9.0 - 11.0 (Fluctuates in that range)
Voltage = 13.6 V
Engine Coolant Temperature = 87.0 Degrees C
Intake Air Temperature = 47.0 Degrees C
Engine rpm = 642
Engine Load = 15.7 %
Throttle Position = 13.7 %
 
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